Co-reporter:Wenkai Zhong, Baobing Fan, Jing Cui, Lei Ying, Feng Liu, Junbiao Peng, Fei Huang, Yong Cao, and Guillermo C. Bazan
ACS Applied Materials & Interfaces October 25, 2017 Volume 9(Issue 42) pp:37087-37087
Publication Date(Web):October 6, 2017
DOI:10.1021/acsami.7b12902
We designed and synthesized two isomeric nonfullerene acceptors, IFBR-p and IFBR-d. These molecular semiconductors contain indacenodithiophene (IDT) as the central unit, adjacent asymmetric 5-fluorobenzo[c][1,2,5]thiadiazole units, and are flanked with rhodanine as the peripheral units. The orientation of the two fluorine atoms (proximal, p, or distal, d), relative to IDT impacts most severely the film morphologies when blended with the electron-donating polymer PTzBI. Polymer solar cells based on PTzBI:IFBR-p give rise to a power conversion efficiency (7.3 ± 0.2%) that is higher than what is achieved with PTzBI:IFBR-d (5.2 ± 0.1%). This difference is attributed to the lower tendency for (over)crystallization by IFBR-p and the resulting more favorable morphology of the photoactive layer. These results highlight the subtle impact of substitution regiochemistry on the properties of nonfullerene acceptors through modulation of their self-assembly tendencies.Keywords: acceptor; fluorobenzo[c][1,2,5]thiadiazole; nonfullerene; polymer solar cells; regiochemistry;
Co-reporter:Gregory C. Welch and Guillermo C. Bazan
Journal of the American Chemical Society March 30, 2011 Volume 133(Issue 12) pp:4632-4644
Publication Date(Web):March 4, 2011
DOI:10.1021/ja110968m
We report on the interaction of Lewis acids with narrow band gap conjugated copolymers containing donor and acceptor units. Examination of the widely used poly[(4,4-bis(2-ethylhexyl)cyclopenta-[2,1-b:3,4-b′]dithiophene)-2,6-(diyl-alt-benzo[2,1,3]thiadiazole)-4,7-diyl] (1) shows weaker binding with B(C6F5)3 when compared with a small molecule that contains a cyclopenta-[2,1-b:3,4-b′]dithiophene (CDT) unit flanked by two benzo[2,1,3]thiadiazole (BT) fragments. Studies on model compounds representative of 1, together with a comparison between B(C6F5)3 and BBr3, indicate that the propensity for Lewis acid coordination is decreased because of steric encumbrance surrounding the BT nitrogen sites. These observations led to the design of chromophores that incorporate an acceptor unit with a more basic nitrogen site, namely pyridal[2,1,3]thiadiazole (PT). That this strategy leads to a stronger B−N interaction was demonstrated through the examination of the reaction of B(C6F5)3 with two small molecules bis(4,4-bis(hexyl)-4H-cyclopenta[2,1-b;3,4-b′]dithiophene)-4,7-pyridal[2,1,3]thiadiazole (8) and bis{2-thienyl-(4,4-bis(hexyl)-4H-cyclopenta[2,1-b;3,4-b′]dithiophene)}-4,7-pyridal[2,1,3]thiadiazole (9) and two polymer systems (poly[(4,4-bis(2-ethylhexyl)cyclopenta-[2,1-b:3,4-b′]dithiophene)-2,6-diyl-alt-([1,2,5]thiadiazolo[3,4-c]pyridine)-4,7-diyl] (10) and poly[(4,4-bis(2-ethylhexyl)cyclopenta-[2,1-b:3,4-b′]dithiophene)-2,6-diyl-alt-(4′,7′-bis(2-thienyl)-[1,2,5]thiadiazolo[3,4-c]pyridine)-5,5-diyl] (11). From a materials perspective, it is worth pointing out that through the binding of B(C6F5)3, new NIR-absorbing polymers can be generated with band gaps from 1.31 to 0.89 eV. A combination of studies involving ultraviolet photoemission spectroscopy and density functional theory shows that the narrowing of the band gap upon borane coordination to the pyridal nitrogen on PT is a result of lowering the energies of both the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of the optically relevant fragments; however, the LUMO is decreased to a greater extent, thereby giving rise to the narrowing of the gap.
Co-reporter:Jung Hwa Seo, Andrea Gutacker, Bright Walker, Shinuk Cho, Andres Garcia, Renqiang Yang, Thuc-Quyen Nguyen, Alan J. Heeger and Guillermo C. Bazan
Journal of the American Chemical Society December 30, 2009 Volume 131(Issue 51) pp:18220-18221
Publication Date(Web):December 7, 2009
DOI:10.1021/ja908441c
To improve injection in n-type organic thin film transistors (OTFTs), a thin conjugated polyelectrolyte (CPE) layer was interposed between electrodes and the semiconductor layer. OTFTs were fabricated with [6,6]-phenyl-C61 butyric acid methyl ester (PCBM) and Au source and drain contacts. We demonstrate that the insertion of CPEs beneath top-contact Au source/drain electrodes can be a very effective strategy for improving the carrier injection and reducing turn-on threshold voltages of n-channel OTFTs. Ultraviolet photoemission spectroscopy (UPS) indicates that the decrease of the electron injection barrier is consistent with organized dipoles at the metal/organic interface.
Co-reporter:Rongrong Cheacharoen, William R. Mateker, Qian Zhang, Bin Kan, Dylan Sarkisian, Xiaofeng Liu, John A. Love, Xiangjian Wan, Yongsheng Chen, Thuc-Quyen Nguyen, Guillermo C. Bazan, Michael D. McGehee
Solar Energy Materials and Solar Cells 2017 Volume 161() pp:368-376
Publication Date(Web):March 2017
DOI:10.1016/j.solmat.2016.12.021
•Both heat and light contribute to 31–66% initial burn-in degradation.•First reported TS80 lifetime (3450–5600 h) of high PCE SM BHJ solar cells.•Post burn-in lifetime of SM BHJ is governed by thermal degradation.•Higher crystallinity active layer solar cells have less photo burn-in.•Larger molecule weight donor contributes to higher thermal stability.Solution-processed small molecule-fullerene bulk heterojunction (SM BHJ) solar cells now have power conversion efficiency (PCE) greater than 10%. However, degradation of SM BHJ solar cells has not been well studied. This work reports the first stability study of six high performance molecules including the record SM BHJ solar cells under device operating conditions. Solar cells with a range of donor molecular weight from 1200 to 2300 Da giving 6–10% PCE are monitored in nitrogen gas under 1 sun illumination with maximum power point tracking as well as at 25 °C and 70 °C in the dark. Both heat and light contribute to initial exponential decay or burn-in with total reduction in efficiency from 31% to 66%. Larger molecules are found to be resistant to heat induced burn-in, while more crystalline active layers are more resistant to light induced burn-in. After burn-in, the linear degradation is observed to be governed by thermal processes. Stabilized TS80 lifetimes of the SM BHJ solar cells range from 3450 h to 5600 h. Molecular design towards higher stability should aim at increasing thermal stability while maintaining crystallinity for photostability.
Co-reporter:Jianyu YuanMichael J. Ford, Yannan Zhang, Huilong Dong, Zhi Li, Youyong Li, Thuc-Quyen NguyenGuillermo C. Bazan, Wanli Ma
Chemistry of Materials 2017 Volume 29(Issue 4) pp:
Publication Date(Web):January 24, 2017
DOI:10.1021/acs.chemmater.6b05365
Narrow band gap conjugated polymers with a D–A–D′–A repeat unit architecture, namely, PF-0, PF-1a, PF-1b, and PF-2, were designed and synthesized. By precisely controlling the orientation of the asymmetric fluorobenzo[c][1,2,5]thiadiazole (FBT) fragments as well as incorporating different electron acceptors benzothiadiazole (BT) and difluorobenzo[c][1,2,5]thiadiazole (DFBT), regioregularity and graded fluorination have been achieved over the polymer backbone. There are evident differences between the properties of PF-1a and PF-1b due to different regioselectivity within the polymer backbone. In addition, the fluorinated analogues can exhibit increased light absorbance, higher electron density in the solid state, a lower-lying valence band, and more ordered solid film structure. The monofluorinated polymer PF-1b with the optimal regioselectivity and bis-fluorinated polymer PF-2 demonstrated improved charge transport as well as thermally resistant film structure (up to 300 °C) in organic field-effect transistors. Moreover, the fluorinated polymers exhibit dramatically increased efficiency from 5.58% to 8.42% in solar cells with lower amount of processing additive, indicating the important role of fluorination and regioselectivity in determining polymer properties. Thus, our systematical study on fluorination may provide an effective approach to precisely control the polymer regioselectivity and improve device performance as well as long-term durability under various environmental stresses.
Co-reporter:Dr. Nathan D. Kirchhofer;Samantha R. McCuskey;Dr. Cheng-Kang Mai; Guillermo C. Bazan
Angewandte Chemie 2017 Volume 129(Issue 23) pp:6619-6622
Publication Date(Web):2017/06/01
DOI:10.1002/ange.201701964
AbstractWe probe anaerobic respiration of bacteria in the presence of conjugated polyelectrolytes (CPEs). Three different CPEs were used to probe how structural variations impact biocurrent generation from Shewanella oneidensis MR-1. For the self-doped anionic CPE only, absorption spectroscopy shows that the addition of S. oneidensis MR-1 leads to the disappearance of the polaron (radical cation) band at >900 nm and an increase in the band at 735 nm due to the neutral species, consistent with electron transfer from microbe to polymer. Microbial three-electrode electrochemical cells (M3Cs) show an increase in the current generated by S. oneidensis MR-1 with addition of the self-doped CPE relative to other CPEs and controls. These experiments combined with in situ cyclic voltammetry suggest that the doped CPE facilitates electron transport to electrodes and reveal structure–function relationships relevant to developing materials for biotic/abiotic interfaces.
Co-reporter:Dr. Bing Wang;Dr. Guangxue Feng;Martin Seifrid;Dr. Ming Wang; Bin Liu; Guillermo C. Bazan
Angewandte Chemie 2017 Volume 129(Issue 50) pp:16279-16282
Publication Date(Web):2017/12/11
DOI:10.1002/ange.201709887
AbstractTwo conjugated oligoelectrolytes (COEs), WMG1 and WMG2, were designed with the goal of achieving near infrared absorption and high photothermal conversion efficiency. Specifically, electron-rich thiophene and electron-poor benzo[1,2-c:4,5-c′]bis[1,2,5]thiadiazole subunits were introduced into the conjugated core to modulate the optical gap and to reduce the fluorescence emission efficiency. WMG1 and WMG2 show absorption maxima at around 800 nm, which favors tissue penetration. Although relatively small in size, WMG1 and WMG2 exhibit photothermal conversion efficiencies of circa 60 % and 54 %, respectively. WMG1 shows dark toxicity to the Gram positive bacterium B. subtilis and good photothermal killing efficiency toward both B. subtilis and Gram negative E. coli, features that demonstrate the promising potential of the COE molecular design for photothermal applications.
Co-reporter:Dr. Nathan D. Kirchhofer;Samantha R. McCuskey;Dr. Cheng-Kang Mai; Guillermo C. Bazan
Angewandte Chemie International Edition 2017 Volume 56(Issue 23) pp:6519-6522
Publication Date(Web):2017/06/01
DOI:10.1002/anie.201701964
AbstractWe probe anaerobic respiration of bacteria in the presence of conjugated polyelectrolytes (CPEs). Three different CPEs were used to probe how structural variations impact biocurrent generation from Shewanella oneidensis MR-1. For the self-doped anionic CPE only, absorption spectroscopy shows that the addition of S. oneidensis MR-1 leads to the disappearance of the polaron (radical cation) band at >900 nm and an increase in the band at 735 nm due to the neutral species, consistent with electron transfer from microbe to polymer. Microbial three-electrode electrochemical cells (M3Cs) show an increase in the current generated by S. oneidensis MR-1 with addition of the self-doped CPE relative to other CPEs and controls. These experiments combined with in situ cyclic voltammetry suggest that the doped CPE facilitates electron transport to electrodes and reveal structure–function relationships relevant to developing materials for biotic/abiotic interfaces.
Co-reporter:Jianyu Yuan;Michael J. Ford;Wanli Ma
Journal of Materials Chemistry A 2017 vol. 5(Issue 19) pp:8903-8908
Publication Date(Web):2017/05/16
DOI:10.1039/C7TA02510F
In comparison with many reported high-efficiency polymer solar cells, only 0.5% (v/v) additive is necessary to optimize a polymer/fullerene (PSFSiF/PC71BM) system, and the power conversion efficiency (PCE) was boosted from 2.4% to 8.0%. 2D grazing incidence wide angle X-ray scattering (GIWAXS) is utilized to understand the relevant structural features in the blend films prepared under different processing conditions, and the BHJ morphology is also examined using atomic force microscopy (AFM) and transmission electron microscopy (TEM) techniques.
Co-reporter:Caitlin McDowell, Guillermo C. Bazan
Current Opinion in Green and Sustainable Chemistry 2017 Volume 5(Volume 5) pp:
Publication Date(Web):1 June 2017
DOI:10.1016/j.cogsc.2017.03.007
•Toxic and/or unsustainable solvents impact the environmental footprint of solution-processed organic solar cells.•Solvent choice modifies the thin film morphology and power conversion efficiency of bulk heterojunction organic solar cells.•Current research is making strides toward using non-chlorinated and non-aromatic solvents.•Focus is on structural modification of materials toward greater solubility in polar media.•Switching to non-fullerene acceptors may decrease solubility constraints.Solution-processed organic solar cells illustrate challenges inherent in processing π-conjugated semiconductors from sustainable polar solvents. The choice of processing conditions strongly influences the self-assembly of the complex multi-component morphology required for effective charge generation and extraction. High power conversion efficiencies have been achieved with a variety of materials and solvents, but greater emphasis on green solvent processing has the potential to make organic solar cells competitive to solar energy alternatives that rely on significantly more toxic compositions.Download high-res image (305KB)Download full-size image
Co-reporter:Jianyu Yuan;Niva A. Ran;Michael J. Ford;Ming Wang;Mahesh Kumar Ravva;Cheng-Kang Mai;Xiaofeng Liu;Jean-Luc Brédas;Thuc-Quyen Nguyen;Wanli Ma
Journal of Materials Chemistry A 2017 vol. 5(Issue 35) pp:18618-18626
Publication Date(Web):2017/09/12
DOI:10.1039/C7TA05442D
Two regioregular narrow bandgap conjugated polymers with a D′–A–D–A repeat unit architecture, namely PIFCF and PSFCF, were designed and synthesized. Both polymers contain strictly organized fluorobenzo[c][1,2,5]thiadiazole (FBT) orientations and different solubilizing side chains for solution processing. Compared to the previously reported asymmetric pyridyl-[2,1,3]thiadiazole (PT) based regioregular polymer, namely PIPCP, PIFCF and PSFCF exhibit wider bandgaps, tighter π–π stacking, and improved hole mobilities. When incorporated into solar cells with fullerene acceptors, the Eloss = Eg − eVoc values of PIFCF and PSFCF devices are increased compared to solar cells based on PIPCP. Determination of Ect in these solar cells reveals that, relative to PIPCP, PIFCF solar cells lose more energy from Eg − Ect, and PSFCF solar cells lose more energy from both Eg − Ect and Ect − eVoc. The close structural relationship between PIPCP and PIFCF provides an excellent framework to establish molecular features that impact the relationship between Eg and Ect. Theoretical calculations predict that Eloss of PIFCF:PC61BM would be higher than in the case of PIPCP:PC61BM, due to greater Eg − Ect. These findings provide insight into the design of high performance, low voltage loss photovoltaic polymeric materials with desirable optoelectronic properties.
Co-reporter:Wenbo Wu, Guillermo C. Bazan, Bin Liu
Chem 2017 Volume 2, Issue 6(Volume 2, Issue 6) pp:
Publication Date(Web):8 June 2017
DOI:10.1016/j.chempr.2017.05.002
Effective sensing, imaging, and therapeutic strategies are of intense research interest for the realization of quick and accurate diagnosis and the treatment of diseases. Among numerous sensing and imaging strategies, fluorescence-based techniques show distinct advantages and offer unique opportunities to address challenges afforded by small quantities of available samples. Thanks to the excellent light-harvesting abilities of conjugated polymers (CPs), the excitation energy along the CP backbones can be transferred to different energy acceptors, resulting in an amplified fluorescence signal and/or photodynamic therapy effects and thus enhancing the efficiency of disease diagnosis and treatment strategies.Signal amplification is one of the simplest and most effective strategies for efficiently improving the performance of emerging sensing, imaging, and therapy technologies. For the amplification of detection signals and enhancement of therapeutic effects, the light-harvesting and energy-transfer properties of conjugated polymers (CPs) have made this class of materials a key platform for amplifying detection signatures that betray the presence of biomarkers and enhancing therapeutic action. In this review, we first summarize CP-amplified fluorescence sensing in homogeneous solution and on solid supports. We then discuss how CPs can be integrated into amplified in vitro and in vivo imaging with the use of both fluorescence and self-luminesce phenomena. We further illustrate and examine the importance of CPs as amplifiers through examples of enhanced photodynamic therapy. To conclude, we discuss the challenges, opportunities, and perspectives for the future development of this field.Download high-res image (171KB)Download full-size image
Co-reporter:Nathan D. Kirchhofer, Zachary D. Rengert, Frederick W. Dahlquist, Thuc-Quyen Nguyen, Guillermo C. Bazan
Chem 2017 Volume 2, Issue 2(Volume 2, Issue 2) pp:
Publication Date(Web):9 February 2017
DOI:10.1016/j.chempr.2017.01.001
•First rationally designed membrane-intercalating conjugated redox molecule, DSFO+•DSFO+ catalyzes transmembrane electron transfer, increasing metabolic efficiency•Under non-toxic conditions, DSFO+ enhances bacterially generated currentBacteria and other microorganisms are self-healing, reaction-specific “nanoreactors” that exist virtually everywhere on earth. As a result of site-to-site variation in the composition of contaminated waters, it is advantageous to boost the metabolic function of naturally dominant bacterial species to aid in contaminant breakdown. If such species can further be used to generate electrical energy at electrodes, this provides a potent means of generating clean power that offsets the cost of treating water in situ. Global adoption of this strategy is prevented, however, because many organisms cannot electrically communicate with an electrode. We therefore designed a chemical additive (DSFO+) that modifies cell membranes for conductivity and boosts power output without toxic side effects. DSFO+ finds immediate relevance in many bioelectronic water-treatment applications, and we anticipate that the molecular design of DSFO+ will inspire the design of additional relevant molecules.For emerging bioelectronic technologies, charge-transfer processes remain rate limited by energy-level mismatching and poor contacts at biotic-abiotic interfaces. Direct chemical modification of these interfaces represents an underdeveloped approach for amplifying biocatalyzed current production. We present the synthesis and application of DSFO+, a redox-active molecule that is designed for membrane affinity and that catalytically couples to biological respiratory transmembrane electron transport, similarly to a heme-containing protein. DSFO+ was employed with three strains of Shewanella oneidensis MR-1 (an electrogenic wild-type and two non-electrogenic knockout mutants) and amplified anodic biocurrent in all strains without toxicity at a physiologically relevant redox potential. Of particular interest, DSFO+ increased metabolic efficiency and biological electron production, thus stimulating respiratory biocurrent production in non-electrogenic bacterial phenotypes. The overall effect is akin to a “protein prosthetic” electron transfer agent.Download high-res image (109KB)Download full-size image
Co-reporter:Guillermo C. Bazan
Science China Chemistry 2017 Volume 60( Issue 8) pp:1109-1110
Publication Date(Web):19 May 2017
DOI:10.1007/s11426-017-9075-9
Co-reporter:Dr. Bing Wang;Dr. Ming Wang;Dr. Alexer Mikhailovsky; Shu Wang; Guillermo C. Bazan
Angewandte Chemie 2017 Volume 129(Issue 18) pp:5113-5116
Publication Date(Web):2017/04/24
DOI:10.1002/ange.201701146
AbstractA membrane-intercalating conjugated oligoelectrolyte (COE), PTTP, was designed and synthesized with the goal of providing red-shifted absorption spectra relative to previously synthesized COE analogs. Specifically, electron-rich and electron-poor subunits were introduced in the conjugated backbone to modulate the band gap. PTTP exhibits maxima of absorption at 507 nm and of emission at 725 nm. PTTP can also efficiently function to generate singlet oxygen in situ (ΦΔ≈20 %) and has appropriate topology and dimensions to interact with lipid membranes. The resulting rapid membrane insertion and sensitizing ability provide PTTP with a highly efficient antibacterial capability under a low light dose (0.6 J cm−2) toward Gram-negative bacteria E. coli, making it a remarkably efficient optically mediated antimicrobial agent.
Co-reporter:Niva A. Ran;John A. Love;Christopher J. Takacs;Aditya Sadhanala;Justin K. Beavers;Samuel D. Collins;Ye Huang;Ming Wang;Richard H. Friend;Thuc-Quyen Nguyen
Advanced Materials 2016 Volume 28( Issue 7) pp:1482-1488
Publication Date(Web):
DOI:10.1002/adma.201504417
Co-reporter:Michael J. Ford;Ming Wang;Hung Phan;Thuc-Quyen Nguyen
Advanced Functional Materials 2016 Volume 26( Issue 25) pp:4472-4480
Publication Date(Web):
DOI:10.1002/adfm.201601294
Many high charge carrier mobility (μ) active layers within organic field-effect transistor (OFET) configurations exhibit non-linear current–voltage characteristics that may drift with time under applied bias and, when applying conventional equations for ideal FETs, may give inconsistent μ values. This study demonstrates that the introduction of electron deficient fullerene acceptors into thin films comprised of the high-mobility semiconducting polymer PCDTPT suppresses an undesirable “double-slope” in the current–voltage characteristics, improves operational stability, and changes ambipolar transport to unipolar transport. Examination of other high μ polymers shows general applicability. This study also shows that one can further reduce instability by tuning the relative electron affinity of the polymer and fullerene by creating blends containing different fullerene derivatives and semiconductor polymers. One can obtain hole μ values up to 5.6 cm2 V–1 s–1 that are remarkably stable over multiple bias-sweeping cycles. The results provide a simple, solution-processable route to dictate transport properties and improve semiconductor durability in systems that display similar non-idealities.
Co-reporter:Hengjing Yan, Zachary D. Rengert, Alexander W. Thomas, Carolin Rehermann, Jamie Hinks and Guillermo C. Bazan
Chemical Science 2016 vol. 7(Issue 9) pp:5714-5722
Publication Date(Web):01 Jun 2016
DOI:10.1039/C6SC00630B
Conjugated oligoelectrolytes (COEs) with phenylenevinylene (PV) repeat units are known to spontaneously intercalate into cell membranes. Twelve COEs, including seven structures reported here for the first time, were investigated for the relationship between their membrane disrupting properties and structural modifications, including the length of the PV backbone and the presence of either a tetraalkylammonium or a pyridinium ionic pendant group. Optical characteristics and interactions with cell membranes were determined using UV-Vis absorption and photoluminescence spectroscopies, and confocal microscopy. Toxicity tests on representative Gram-positive (Enterococcus faecalis) and Gram-negative (Escherichia coli) bacteria reveal generally greater toxicity to E. faecalis than to E. coli and indicate that shorter molecules have superior antimicrobial activity. Increased antimicrobial potency was observed in three-ring COEs appended with pyridinium ionic groups but not with COEs with four or five PV repeat units. Studies with mutants having cell envelope modifications indicate a possible charge based interaction with pyridinium-appended compounds. Fluorine substitutions on COE backbones result in structures that are less toxic to E. coli, while the addition of benzothiadiazole to COE backbones has no effect on increasing antimicrobial function. A weakly membrane-intercalating COE with only two PV repeat units allowed us to determine the synthetic limitations as a result of competition between solubility in aqueous media and association with cell membranes. We describe, for the first time, the most membrane disrupting structure achievable within two homologous series of COEs and that around a critical three-ring backbone length, structural modifications have the most effect on antimicrobial activity.
Co-reporter:Chelsea Catania, Alexander W. Thomas and Guillermo C. Bazan
Chemical Science 2016 vol. 7(Issue 3) pp:2023-2029
Publication Date(Web):03 Dec 2015
DOI:10.1039/C5SC03046C
Cationic conjugated oligoelectrolytes (COEs) varying in length and structural features are compared with respect to their association with E. coli and their effect on cell surface charge as determined by zeta potential measurements. Regardless of structural features, at high staining concentrations COEs with longer molecular dimensions associate less, but neutralize the negative surface charge of E. coli to a greater degree than shorter COEs.
Co-reporter:Stephanie L. Fronk, Ming Wang, Michael Ford, Jessica Coughlin, Cheng-Kang Mai and Guillermo C. Bazan
Chemical Science 2016 vol. 7(Issue 8) pp:5313-5321
Publication Date(Web):03 May 2016
DOI:10.1039/C6SC00908E
Two narrow bandgap conjugated polymers containing chiral 2-ethylhexyl side chains were synthesized: poly[(4,4-bis(2-ethylhexyl)cyclopenta-[2,1-b:3,4-b′]dithiophene)-2,6-diyl-alt-(2,1,3-benzothiadiazole)-4,7-diyl] (PCPDTBT*) and poly[(4,4-bis(2-ethylhexyl)cyclopenta[2,1-b:3,4-b0]dithiophene)-2,6-diyl-alt-[1,2,5]-thiadiazolo[3,4-c]pyridine] (PCDTPT*). The presence of a chiral substituent provides a handle to study the geometry of interchain aggregates and/or the secondary structure of these conjugated polymers in solution and in thin films via circular dichroism (CD) spectroscopy, provided that the asymmetry in the side-chain is translated to the optically active conjugated backbone. CD signals are observed for PCPDTBT* and PCDTPT* in poor solvent systems, which indicate the presence of chiral ordering in the aggregates. PCPDTBT* shows greater chiral order than PCDTPT* based on their relative anisotropy factors. Additionally, GIWAXS analysis reveals that PCPDTBT* films are more ordered than what is observed for the same polymer containing racemic 2-ethylhexyl chains. Upon solution deposition, the chiral ordering is found to translate to the solid-state microstructure for PCPDTBT* but not PCDTPT*. The presence of a pyridyl nitrogen on the thiadiazolo[3,4-c]pyridine ring of PCDTPT* favors a planar conformation for the backbone such that it has a higher rotational barrier compared to PCPDTBT*. This larger rotational barrier appears to limit the ability of PCDTPT* to adopt a helical structure or relevant chain distortions for achieving chiral aggregates.
Co-reporter:Michael J. Ford, Ming Wang, Shrayesh N. Patel, Hung Phan, Rachel A. Segalman, Thuc-Quyen Nguyen, and Guillermo C. Bazan
Chemistry of Materials 2016 Volume 28(Issue 5) pp:1256
Publication Date(Web):February 4, 2016
DOI:10.1021/acs.chemmater.5b04774
Co-reporter:Jianyu Yuan, Caitlin McDowell, Cheng-Kang Mai, Guillermo C. Bazan, and Wanli Ma
Chemistry of Materials 2016 Volume 28(Issue 20) pp:7479
Publication Date(Web):September 21, 2016
DOI:10.1021/acs.chemmater.6b03189
In contrast to the great efforts on developing novel donor (D)–acceptor (A) copolymers, research on investigating the backbone composition of conjugated polymer is rare. In this contribution, we disclose the design and synthesis of a ternary D1–D2–A–D2 structured conjugated polymer PBSF. Compared to the typical D–A polymer with fixed D/A moiety number, the ternary structure can tune the optical and electrical properties more comprehensively and delicately. Precisely control of the ternary fragments relative to the backbone vector was achieved, further promoting sufficient planar structure, strong intermolecular packing, and excellent charge transport. Finally, the additive and annealing-free polymer solar cells based on PBSF and phenyl-C71-butyric acid methyl ester ([70]PCBM; PCE = 7.4%) or cheap, nonfunctionalized C70 (PCE = 5.3%) demonstrate excellent performance using either chlorinated or nonhalogenated “green” solvent. We believe that this novel and efficient ternary structure may spark future polymer design to achieve sustainable-processed photovoltaic devices for practical mass production.
Co-reporter:Ming Wang, Michael Ford, Hung Phan, Jessica Coughlin, Thuc-Quyen Nguyen and Guillermo C. Bazan
Chemical Communications 2016 vol. 52(Issue 15) pp:3207-3210
Publication Date(Web):19 Jan 2016
DOI:10.1039/C5CC10009G
Four conjugated copolymers with a donor/acceptor architecture comprising 4,4-dihexadecyl-4H-cyclopenta[1,2-b:5,4-b′]dithiophene as the donor structural unit and benzo[2,1,3]thiadiazole fragments with varying degrees of fluorination as the acceptor structural units have been synthesized and characterized. It has been shown that the energy levels were decreased after the fluorine substitution. The field-effect charge carrier mobility was similar for all polymers with less than an order of magnitude difference between different acceptor units.
Co-reporter:Nan Hu, Cheng-Kang Mai, Glenn H. Fredrickson and Guillermo C. Bazan
Chemical Communications 2016 vol. 52(Issue 11) pp:2237-2240
Publication Date(Web):30 Nov 2015
DOI:10.1039/C5CC09200K
A simple, one-pot approach to synthesize random semicrystalline/amorphous multiblock copolymers (12–17 blocks per chain on average) is demonstrated that takes advantage of acyclic diene metathesis (ADMET) polymerization of α,ω-divinyl-terminated telechelic polyolefins. This synthetic approach offers a generic, viable and economical route to polyolefin-based multiblock copolymers and may be extendable to broader families of multiblock materials.
Co-reporter:Vinay Gupta, Lai Fan Lai, Ram Datt, Suresh Chand, Alan J. Heeger, Guillermo C. Bazan and Surya Prakash Singh
Chemical Communications 2016 vol. 52(Issue 55) pp:8596-8599
Publication Date(Web):07 Jun 2016
DOI:10.1039/C6CC03998G
A molecular donor of intermediate dimensions based on dithienogermole (DTG) as the central electron rich unit, coded as DTG(FBT2Th2)2, was designed and synthesized for use in bulk heterojunction, solution-processed organic solar cells. Under optimized conditions, a maximum power conversion efficiency (PCE) of 9.1% can be achieved with [6,6]-phenyl C71-butyric acid methyl ester (PC71BM) as the acceptor semiconductor component.
Co-reporter:Yueqin Shi, Cheng-Kang Mai, Stephanie L. Fronk, Yiwang Chen, and Guillermo C. Bazan
Macromolecules 2016 Volume 49(Issue 17) pp:6343-6349
Publication Date(Web):August 15, 2016
DOI:10.1021/acs.macromol.6b00965
A series of conjugated polyelectrolytes (CPEs) based on an electron-deficient polybenzotriazole backbone with various pendant ionic functionalized side chains were synthesized directly from the corresponding ionic monomers. Of particular interest was to use the different chemical structures to understand how the optical features are influenced by the ionic side chains. We found that interchain aggregation is favored in low dielectric constant solvents for cationic CPEs. Moreover, aggregated species absorb at longer wavelengths and exhibit higher fluorescence quantum yields.
Co-reporter:Stephanie L. Fronk, Yueqin Shi, Martin Siefrid, Cheng-Kang Mai, Caitlin McDowell, and Guillermo C. Bazan
Macromolecules 2016 Volume 49(Issue 24) pp:9301-9308
Publication Date(Web):December 15, 2016
DOI:10.1021/acs.macromol.6b02229
Conjugated polymers containing alternating thiophene units and benzotriazole structural units bearing either chiral (S)-2-ethylhexyl (PBTz-Th*) or racemic 2-ethylhexyl side chains (PBTz-Th) were synthesized. Characterization by optical absorption spectroscopy of both PBTz-Th* and its racemic counterpart reveal aggregated chains, even at dilute concentrations in good solvents. The presence of a chiral substituent permits characterization via circular dichroism (CD) spectroscopy. CD spectra provide evidence of chiral aggregates of PBTz-Th* chains even at 0.01 mg/mL in dichlorobenzene. When PBTz-Th* solutions are diluted with PBTz-Th, the resulting CD spectrum suggests that PBTz-Th* chains are chiral in the aggregate. Chiral ordering is also found to translate from aggregates in solution to the solid state.
Co-reporter:Cheng-Kang Mai, Jun Liu, Christopher M. Evans, Rachel A. Segalman, Michael L. Chabinyc, David G. Cahill, and Guillermo C. Bazan
Macromolecules 2016 Volume 49(Issue 13) pp:4957-4963
Publication Date(Web):June 23, 2016
DOI:10.1021/acs.macromol.6b00546
We report a method to determine the thermal conductivities of polymer composites with single-walled carbon nanotubes (SWNTs) using time-domain thermoreflectance. Both through-plane and in-plane thermal conductivities were determined. Two types of CPEs used in these studies are of the same conjugated backbone but with either cationic (CPE-PyrBIm4) or anionic (CPE-Na) pendant functionalities. The CPE-Na/SWNT composites are p-type conductors, whereas the CPE-PyrBIm4/SWNT counterparts exhibit n-type charge transport. The CPE/SWNT films were prepared through a filtration method that preferentially aligns the SWNTs in the in-plane direction. Attaching the composites onto glass substrates with a precoated heat transducer allows one to measure the through-plane thermal conductivity of materials with rough surfaces. The in-plane thermal conductivity can be measured by embedding thick samples into epoxy followed by microtoming to expose the relatively smooth cross sections. The thermal conductivity along the in-plane direction is found to be higher than that along the through-plane direction. Indeed, the anisotropy factor of thermal conductivity in these composites is approximately an order of magnitude, favoring in-plane direction.
Co-reporter:Yue Xing, Chen Sun, Hin.-Lap. Yip, Guillermo C. Bazan, Fei Huang, Yong Cao
Nano Energy 2016 Volume 26() pp:7-15
Publication Date(Web):August 2016
DOI:10.1016/j.nanoen.2016.04.057
•A new series of hydrophilic fullerene derivatives was introduced as ETLs in PVKSCs.•OE chains could passivate trap states of perovskite and reduce the WF of cathode.•A full analysis using controlled electron density in passivators was demonstrated.•The underlying mechanism of trap passivation was better understood in this work.•A high PCE of 16.0% has been achieved.Defect states within perovskite crystals are thought to induce undesired charge recombination and photocurrent hysteresis in perovskite solar cells. Although the processing of perovskite films with electron-rich molecules that can efficiently passivate the surface traps, the exact mechanism remains unclear. As the electron-rich units are key components for such a function, a rigorous analysis using controlled electron density in passivators can provide the means to understand these underlying mechanisms and thereby improve future improvements. In the study reported here, we combined electron-rich functional groups with fullerenes to design a new series of hydrophilic fullerene derivatives, in which each phenyl group of the diphenylmethanofullerene (DPM) moiety was decorated with an oligoether (OE) side group. These new materials were introduced as alternative electron transport layers (ETLs) to replace the commonly used PCBM in p-i-n planar-heterojunction perovskite solar cells. Our tests indicate that electron-rich OE chains can both passivate perovskite trap states and reduce the work function of the metal cathode. By adjusting the numbers of OE chains, relevant properties such as the energy levels, charge carrier mobilities, surface energy and dipole layer features could be tuned at the interfaces. Furthermore, devices with these fullerene ETLs showed significant improvements in power conversion efficiency (PCE) compared to devices with PCBM ETLs. A high PCE of 16% was achieved by applying the monoadduct fullerene derivative C70-DPM-OE as the ETL of the device.
Co-reporter:Cheng-Kang Mai, Boris Russ, Stephanie L. Fronk, Nan Hu, Mary B. Chan-Park, Jeffrey J. Urban, Rachel A. Segalman, Michael L. Chabinyc and Guillermo C. Bazan
Energy & Environmental Science 2015 vol. 8(Issue 8) pp:2341-2346
Publication Date(Web):30 Apr 2015
DOI:10.1039/C5EE00938C
Single-walled carbon nanotubes can be selectively doped by conjugated polyelectrolytes (CPEs) to form either p- or n-type composites. The selectivity of charge-transfer doping is found to be dictated by the polarities of CPE pendant ionic functionalities. This finding leads to a fundamentally new approach to both p- and n-type solution-processable composites for high performance, flexible thermoelectric devices.
Co-reporter:Nathan D. Kirchhofer, Michelle A. Rasmussen, Frederick W. Dahlquist, Shelley D. Minteer and Guillermo C. Bazan
Energy & Environmental Science 2015 vol. 8(Issue 9) pp:2698-2706
Publication Date(Web):06 Jul 2015
DOI:10.1039/C5EE01707F
The photobioelectrochemical impact of a series of conjugated oligoelectrolytes (COEs) with a systematic progression of chemical structures was elucidated by their direct incorporation into thylakoid bioanodes. In both three-electrode electrochemical cells and bio-solar cell devices, significant anodic performance enhancements (p < 0.1) were observed when anodes were modified with certain COEs. Amperometric photocurrent densities increased by up to 2.3-fold for the best COE. In bio-solar cell devices, short-circuit photocurrent increased by up to 1.7-fold and short-circuit dark current increased by up to 1.4-fold, indicating that the best COEs enhance both photocurrent generation and interfacial electron transfer. Trends in these results indicate that the molecular length and pendant charge of COEs differentially contribute to photobioelectrochemical enhancements, and the optimal combination of these features is revealed. Control experiments indicate that COEs augment native thylakoid functionality, as COEs do not have redox activity or undergo chemical degradation.
Co-reporter:Hengjing Yan;Chern Chuang;Andriy Zhugayevych;Sergei Tretiak;Frederick W. Dahlquist
Advanced Materials 2015 Volume 27( Issue 11) pp:1908-1911
Publication Date(Web):
DOI:10.1002/adma.201404167
Co-reporter:Hengjing Yan;Chelsea Catania
Advanced Materials 2015 Volume 27( Issue 19) pp:2958-2973
Publication Date(Web):
DOI:10.1002/adma.201500487
Conjugated oligoelectrolytes (COEs), molecules that are defined by a π-delocalized backbone and terminal ionic pendant groups, have been previously demonstrated to effectively reduce charge-injection/extraction barriers at metal/organic interfaces in thin-film organic-electronic devices. Recent studies demonstrate a spontaneous affinity of certain COEs to intercalate into, and align within, lipid bilayers in an ordered orientation, thereby allowing modification of membrane properties and the functions of microbes in bioelectrochemical and photosynthetic systems. Several reports have provided evidence of enhanced current generation and bioproduction. Mechanistic approaches suggest that COEs influence microbial extracellular electron transport to abiotic electrode surfaces via more than one proposed pathway, including direct electron transfer and meditated electron transfer. Molecular dynamics simulations as a function of molecular structure suggest that insertion of cationic COEs results in membrane thinning as the lipid phosphate head groups are drawn toward the center of the bilayer. Since variations in molecular structures, especially the length of the conjugated backbone, distribution of ionic groups, and hydrophobic substitutions, show an effect on their antimicrobial properties, preferential cell localization, and microbial selection, it is promising to further design novel membrane-intercalating molecules based on COEs for practical applications, including energy generation, environmental remediation, and antimicrobial treatment.
Co-reporter:Caitlin McDowell;Maged Abdelsamie;Kui Zhao;Detlef-M. Smilgies;Aram Amassian
Advanced Energy Materials 2015 Volume 5( Issue 18) pp:
Publication Date(Web):
DOI:10.1002/aenm.201501121
The addition of polystyrene (PS), a typical insulator, is empirically shown to increase the power conversion efficiencies (PCEs) of a solution-deposited bulk heterojunction (BHJ) molecular blend film used in solar cell fabrication: p-DTS(FBTTh2)2/PC71BM. The performance is further improved by small quantities of diiodooctane (DIO), an established solvent additive. In this study, how the addition of PS and DIO affects the film formation of this bulk heterojunction blend film are probed via in situ monitoring of absorbance, thickness, and crystallinity. PS and DIO additives are shown to promote donor crystallite formation on different time scales and through different mechanisms. PS-containing films retain chlorobenzene solvent, extending evaporation time and promoting phase separation earlier in the casting process. This extended time is insufficient to attain the morphology for optimal PCE results before the film sets. Here is where the presence of DIO comes into play: its low vapor pressure further extends the time scale of film evolution and allows for crystalline rearrangement of the donor phase long after casting, ultimately leading to the best BHJ organization.
Co-reporter:Ji-Eun Jeong, Boram Kim, Shinjae Woo, Sungu Hwang, Guillermo C. Bazan and Han Young Woo
Chemical Science 2015 vol. 6(Issue 3) pp:1887-1894
Publication Date(Web):07 Jan 2015
DOI:10.1039/C4SC03258F
A strategy to extend the detection range of weakly-binding targets is reported that takes advantage of fluorescence resonance energy transfer (FRET)-based bioassays based on molecular beacon aptamers (MBAs) and cationic conjugated polyelectrolytes (CPEs). In comparison to other aptamer-target pairs, the aptamer-based adenosine triphosphate (ATP) detection assays are limited by the relatively weak binding between the two partners. In response, a series of MBAs were designed that have different stem stabilities while keeping the constant ATP-specific aptamer sequence in the loop part. The MBAs are labeled with a fluorophore and a quencher at both termini. In the absence of ATP, the hairpin MBAs can be opened by CPEs via a combination of electrostatic and hydrophobic interactions, showing a FRET-sensitized fluorophore signal. In the presence of ATP, the aptamer forms a G-quadruplex and the FRET signal decreases due to tighter contact between the fluorophore and quencher in the ATP/MBA/CPE triplex structure. The FRET-sensitized signal is inversely proportional to [ATP]. The extension of the detection range is determined by the competition between opening of the ATP/MBA G-quadruplex by CPEs and the composite influence by ATP/aptamer binding and the stem interactions. With increasing stem stability, the weak binding of ATP and its aptamer is successfully compensated to show the resistance to disruption by CPEs, resulting in a substantially broadened detection range (from millimolar up to nanomolar concentrations) and a remarkably improved limit of detection. From a general perspective, this strategy has the potential to be extended to other chemical- and biological-assays with low target binding affinity.
Co-reporter:Guangxue Feng, Cheng-Kang Mai, Ruoyu Zhan, Guillermo C. Bazan and Bin Liu
Journal of Materials Chemistry A 2015 vol. 3(Issue 37) pp:7340-7346
Publication Date(Web):06 Aug 2015
DOI:10.1039/C5TB01118C
We report the demonstration of antimicrobial conjugated polyelectrolytes (CPEs) with high NIR absorbance for selective and efficient photothermal killing of bacteria over mammalian cells. The antimicrobial CPE possessing quaternary ammonium (QA) terminated side chains (P1) shows higher binding preference and increased dark toxicity towards Gram-positive and Gram-negative bacteria over mammalian cells. Bestowed by π-conjugated backbones, P1 exhibits a high molar absorptivity of 39.8 L g−1 cm−1 at 808 nm with an efficient photothermal conversion efficiency of 33 ± 1%. Upon 808 nm laser irradiation, P1 shows enhanced bactericidal effects, but not to mammalian cells. Although the anionic CPE counterpart with the same polymer backbone but sulfonate terminated side chains (P2) possesses a similar photothermal conversion ability, it exhibits much lower antibacterial effects due to its low binding affinity. This study thus reveals that bacteria–CPE electrostatic interactions play a major role in bacterial recognition, although hydrophobic interactions also contribute.
Co-reporter:Cheng-Kang Mai, Tomoya Arai, Xiaofeng Liu, Stephanie L. Fronk, Gregory M. Su, Rachel A. Segalman, Michael L. Chabinyc and Guillermo C. Bazan
Chemical Communications 2015 vol. 51(Issue 99) pp:17607-17610
Publication Date(Web):28 Sep 2015
DOI:10.1039/C5CC06690E
We report the synthesis of a series of water-soluble anionic narrow band-gap conjugated polyelectrolytes with a varied density of the ionic functional groups. The charge density is modulated by incorporating the structural units with tetraethylene glycol (TEG) monomethyl ether side chains. These polymers are readily p-doped during dialysis in water. CPEs with TEG side chains exhibit tighter intermolecular packing in the solid state and higher electrical conductivity.
Co-reporter:A. W. Thomas, C. Catania, L. E. Garner and G. C. Bazan
Chemical Communications 2015 vol. 51(Issue 45) pp:9294-9297
Publication Date(Web):01 May 2015
DOI:10.1039/C5CC01724F
Conjugated oligoelectrolytes (COEs) bearing pyridinium and carboxylate groups are synthesized, characterized, and compared to the trimethylammonium analogue from which they are derived. All COEs are able to spontaneously intercalate into liposomes, whereas only positively charged COEs intercalate into E. coli membranes. Membrane intercalation is determined necessary for performance enhancement in microbial fuel cells.
Co-reporter:Xiaofeng Liu, Mark A. Burgers, Ben B. Y. Hsu, Jessica E. Coughlin, Louis A. Perez, Alan J. Heeger and Guillermo C. Bazan
RSC Advances 2015 vol. 5(Issue 108) pp:89144-89148
Publication Date(Web):12 Oct 2015
DOI:10.1039/C5RA19606J
Four isomorphic organic semiconductors are compared to map out how the precision of chemical structures determines solid state molecular organization. Intramolecular electronic structure and intermolecular packing preference in the solid state were shown to be exclusively dependent on the relative location of the electron accepting fragments within a given molecule.
Co-reporter:Huiqiong Zhou, Yuan Zhang, Cheng-Kang Mai, Jason Seifter, Thuc-Quyen Nguyen, Guillermo C. Bazan, and Alan J. Heeger
ACS Nano 2015 Volume 9(Issue 1) pp:371
Publication Date(Web):December 15, 2014
DOI:10.1021/nn505378m
The intrinsic acidic nature of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) hole-transporting layer (HTL) induces interfacial protonation and limits the device performance in organic solar cells based on basic pyridylthiadiazole units. By utilizing a pH neutral, water/alcohol soluble conjugated polyelectrolyte CPE-K as the HTL in p-DTS(PTTh2)2:PC71BM solar cells, a 60% enhancement in PCE has been obtained with an increased Vbi, reduced Rs, and improved charge extraction. These effects originate from the elimination of interfacial protonation and energy barrier compared with the PEDOT:PSS HTL.Keywords: bulk heterojunctions; hole-transporting layers; interface engineering; interfacial interaction; organic solar cells;
Co-reporter:Stephanie L. Fronk, Cheng-Kang Mai, Michael Ford, Ryan P. Noland, and Guillermo C. Bazan
Macromolecules 2015 Volume 48(Issue 17) pp:6224-6232
Publication Date(Web):August 19, 2015
DOI:10.1021/acs.macromol.5b00986
The solid-state microstructure of semiconducting polymers is known to influence properties relevant for their function in optoelectronic devices. While several strategies exist in the literature for controlling desired morphological organization, preaggregation in solution via polymer chain end-functionalization remains relatively unexplored. In this work, we synthesized two poly(3-hexylthiophene) (P3HT) derivatives with different end-groups by using click chemistry. End-groups chosen for this study were derivatives of sulforhodamine 101 dye and phenyl-C61-butyric acid methyl ester (PC60BM). The chemical functionality of the end-group is found to influence the aggregation properties as a function of solvent quality. End-group-induced preaggregation ultimately impacts the optical properties and molecular orientation in the solid state. These results suggest future applications of this structural modification strategy to modulate device characteristics.
Co-reporter:Ye Huang, Edward J. Kramer, Alan J. Heeger, and Guillermo C. Bazan
Chemical Reviews 2014 Volume 114(Issue 14) pp:7006
Publication Date(Web):May 28, 2014
DOI:10.1021/cr400353v
Co-reporter:Huiqiong Zhou;Yuan Zhang;Cheng-Kang Mai;Samuel D. Collins;Thuc-Quyen Nguyen;Alan J. Heeger
Advanced Materials 2014 Volume 26( Issue 5) pp:780-785
Publication Date(Web):
DOI:10.1002/adma.201302845
Co-reporter:Nekane Guarrotxena
Advanced Materials 2014 Volume 26( Issue 12) pp:1941-1946
Publication Date(Web):
DOI:10.1002/adma.201304107
Co-reporter:Hsin-Rong Tseng;Hung Phan;Chan Luo;Ming Wang;Louis A. Perez;Shrayesh N. Patel;Lei Ying;Edward J. Kramer;Thuc-Quyen Nguyen;Alan J. Heeger
Advanced Materials 2014 Volume 26( Issue 19) pp:2993-2998
Publication Date(Web):
DOI:10.1002/adma.201305084
Co-reporter:Ye Huang;Wen Wen;Subhrangsu Mukherjee;Harald Ade;Edward J. Kramer
Advanced Materials 2014 Volume 26( Issue 24) pp:4168-4172
Publication Date(Web):
DOI:10.1002/adma.201400497
Co-reporter:Yao Li;Cheng-Kang Mai;Hung Phan;Xiaofeng Liu;Thuc-Quyen Nguyen;Mary B. Chan-Park
Advanced Materials 2014 Volume 26( Issue 27) pp:4697-4703
Publication Date(Web):
DOI:10.1002/adma.201400612
Co-reporter:Liheng Feng;Libing Liu;Fengting Lv;Shu Wang
Advanced Materials 2014 Volume 26( Issue 23) pp:3926-3930
Publication Date(Web):
DOI:10.1002/adma.201305206
Co-reporter:Ye Huang;Xiaofeng Liu;Cheng Wang;James T. Rogers;Gregory M. Su;Michael L. Chabinyc;Edward J. Kramer
Advanced Energy Materials 2014 Volume 4( Issue 10) pp:
Publication Date(Web):
DOI:10.1002/aenm.201301886
The ratio of the donor and acceptor components in bulk heterojunction (BHJ) organic solar cells is a key parameter for achieving optimal power conversion efficiency (PCE). However, it has been recently found that a few BHJ blends have compositional tolerance and achieve high performance in a wide range of donor to acceptor ratios. For instance, the X2:PC61BM system, where X2 is a molecular donor of intermediate dimensions, exhibits a PCE of 6.6%. Its PCE is relatively insensitive to the blend ratio over the range from 7:3 to 4:6. The effect of blend ratio of X2/PC61BM on morphology and device performance is therefore systematically investigated by using the structural characterization techniques of energy-filtered transmission energy microscopy (EF-TEM), resonant soft X-ray scattering (R-SoXS) and grazing incidence wide angle X-ray scattering (GIWAXS). Changes in blend ratio do not lead to obvious differences in morphology, as revealed by R-SoXS and EF-TEM. Rather, there is a smooth evolution of a connected structure with decreasing domain spacing from 8:2 to 6:4 blend ratios. Domain spacing remains constant from 6:4 to 4:6 blend ratios, which suggests the presence of continuous phases with proper domain size that may provide access for charge carriers to reach their corresponding electrodes.
Co-reporter:Xiaofeng Liu ; Yanming Sun ; Ben B. Y. Hsu ; Andreas Lorbach ; Li Qi ; Alan J. Heeger
Journal of the American Chemical Society 2014 Volume 136(Issue 15) pp:5697-5708
Publication Date(Web):March 24, 2014
DOI:10.1021/ja413144u
Increases in the molecular length of narrow band gap conjugated chromophores reveal potentially beneficial optical and electronic properties, thermal stabilities, and high power conversion efficiencies when integrated into optoelectronic devices, such as bulk heterojunction organic solar cells. With the objective of providing useful information for understanding the transition from small-sized molecules to polymers, as well as providing a general chemical design platform for extracting relationships between molecular structure and bulk properties, we set out to vary the electron affinity of the molecular backbone. Therefore, a series of donor (D)–acceptor (A) alternating narrow band gap conjugated chromophores were synthesized based on the general molecular frameworks: D1-A1-D2-A2-D2-A1-D1 and D1-A1-D2-A2-D2-A2-D2-A1-D1. When the central electron-accepting moiety (A2) was varied or modified, two classes of molecules could be compared. First, we showed that the alteration of one single electron-accepting group, while maintaining the shape of the molecular framework, can effectively impact the optical properties and energy levels of the molecules. DFT ground state structure optimizations show similar “U” shape conformations among these molecules. Second, we examined how the site-specific introduction of fluorine atom(s) modifies the thermal properties in the solid state, while maintaining relatively similar optical and electrochemical features of interest. Structure–property relationship of such molecular systems could be rationally evaluated in the aspects of thermal-responsive molecular organizations in the solid state and dipole moments both in the ground and excited states. The impact of molecular structure on charge carrier mobilities in field effect transistors and the performance of photovoltaic devices were also studied.
Co-reporter:Cheng-Kang Mai ; Ruth A. Schlitz ; Gregory M. Su ; Daniel Spitzer ; Xiaojia Wang ; Stephanie L. Fronk ; David G. Cahill ; Michael L. Chabinyc
Journal of the American Chemical Society 2014 Volume 136(Issue 39) pp:13478-13481
Publication Date(Web):September 2, 2014
DOI:10.1021/ja504284r
This contribution reports a series of anionic narrow-band-gap self-doped conjugated polyelectrolytes (CPEs) with π-conjugated cyclopenta-[2,1-b;3,4-b′]-dithiophene-alt-4,7-(2,1,3-benzothiadiazole) backbones, but with different counterions (Na+, K+, vs tetrabutylammonium) and lengths of alkyl chains (C4 vs C3). These materials were doped to provide air-stable, water-soluble conductive materials. Solid-state electrical conductivity, thermopower, and thermal conductivity were measured and compared. CPEs with smaller counterions and shorter side chains exhibit higher doping levels and form more ordered films. The smallest countercation (Na+) provides thin films with higher electrical conductivity, but a comparable thermopower, compared to those with larger counterions, thereby leading to a higher power factor. Chemical modifications of the pendant side chains do not influence out of plane thermal conductivity. These studies introduce a novel approach to understand thermoelectric performance by structural modifications.
Co-reporter:Daniel Tordera ; Martijn Kuik ; Zachary D. Rengert ; Enrico Bandiello ; Henk J. Bolink ; Guillermo C. Bazan ;Thuc-Quyen Nguyen
Journal of the American Chemical Society 2014 Volume 136(Issue 24) pp:8500-8503
Publication Date(Web):May 26, 2014
DOI:10.1021/ja502055x
Conjugated polyelectrolytes (CPEs) are versatile materials used in a range of organic optoelectronic applications. Because of their ionic/electronic nature, characterizing these materials is nontrivial, and their operational mechanism is not fully understood. In this work we use a methodology that combines constant-voltage-driven current-density transient measurements with fast current vs voltage scans to allow decoupling of ionic and electronic phenomena. This technique is applied to diodes prepared with cationic CPEs having different charge-compensating anions. Our results indicate that the operational mechanism of these devices is governed by electrochemical doping of the CPE. On the basis of the notion that the saturated depletion layer for the anions consists of the same π-conjugated backbone material, we discern how the extent and speed of formation of the doped region depend on the anion structure. Apart from addressing fundamental transport questions, this work provides a tool for future characterization of different CPEs and other similar systems.
Co-reporter:John A. Love ; Ikuhiro Nagao ; Ye Huang ; Martijn Kuik ; Vinay Gupta ; Christopher J. Takacs ; Jessica E. Coughlin ; Li Qi ; Thomas S. van der Poll ; Edward J. Kramer ; Alan J. Heeger ; Thuc-Quyen Nguyen
Journal of the American Chemical Society 2014 Volume 136(Issue 9) pp:3597-3606
Publication Date(Web):February 13, 2014
DOI:10.1021/ja412473p
A novel solution-processable small molecule, namely, benzo[1,2-b:4,5-b]bis(4,4′-dihexyl-4H-silolo[3,2-b]thiophene-2,2′-diyl)bis(6-fluoro-4-(5′-hexyl-[2,2′-bithiophene]-5-yl)benzo[c][1,2,5]thiadiazole (p-SIDT(FBTTh2)2), was designed and synthesized by utilizing the silaindacenodithiophene (SIDT) framework as the central D2 donor unit within the D1AD2AD1 chromophore configuration. Relative to the widely studied 7,7′-[4,4-bis(2-ethylhexyl)-4H-silolo[3,2-b:4,5-b′]dithiophene-2,6-diyl]bis[6-fluoro-4-(5′-hexyl-[2,2′-bithiophene]-5-yl)benzo[c][1,2,5]thiadiazole] (p-DTS(FBTTh2)2), which contains the stronger donor fragment dithienosilole (DTS) as D2, one finds that p-SIDT(FBTTh2)2 exhibits a wider band gap and can be used to fabricate bulk heterojunction solar cells with higher open circuit voltage (0.91 V). Most remarkably, thin films comprising p-SIDT(FBTTh2)2 can achieve exceptional levels of self-organization directly via solution deposition. For example, high-resolution transmission electron microscopy analysis shows that p-SIDT(FBTTh2)2 spin-cast from chlorobenzene organizes into crystalline domains with lattice planes that extend over length scales on the order of hundreds of nanometers. Such features suggest liquid crystalline properties during the evolution of the film. Moreover, grazing incidence wide-angle X-ray scattering analysis shows a strong tendency for the molecules to exist with a strong “face-on” orientation relative to the substrate plane. Similar structural features, albeit of more restricted dimensions, can be observed within p-SIDT(FBTTh2)2:PC71BM bulk heterojunction thin films when the films are processed with 0.4% diiodooctane (DIO) solvent additive. DIO use also increases the solar cell power conversion efficiencies (PCEs) from 1.7% to 6.4%. Of significance from a practical device fabrication perspective is that, for p-SIDT(FBTTh2)2:PC71BM blends, there is a wide range of compositions (from 20:80 to 70:30 p-SIDT(FBTTh2)2:PC71BM) that provide good photovoltaic response, i.e., PCE = 4–6%, indicating a robust tendency to form the necessary continuous phases for charge carrier collection. Light intensity photocurrent measurements, charge selective diode fabrication, and internal quantum efficiency determinations were carried out to obtain insight into the mechanism of device operation. Inclusion of DIO in the casting solution results in films that exhibit much lower photocurrent dependence on voltage and a concomitant increase in fill factor. At the optimum blend ratio, devices show high charge carrier mobilities, while mismatched hole and electron mobilities in blends with high or low donor content result in reduced fill factors and device performance.
Co-reporter:Alexander W. Thomas ; Zachary B. Henson ; Jenny Du ; Carol A. Vandenberg
Journal of the American Chemical Society 2014 Volume 136(Issue 10) pp:3736-3739
Publication Date(Web):February 27, 2014
DOI:10.1021/ja412695w
A near-IR-emitting conjugated oligoelectrolyte (COE), ZCOE, was synthesized, and its photophysical features were characterized. The biological affinity of ZCOE is compared to that of an established lipid-membrane-intercalating COE, DSSN+, which has blue-shifted optical properties making it compatible for tracking preferential sites of accumulation. ZCOE exhibits diffuse staining of E. coli cells, whereas it displays internal staining of select yeast cells which also show propidium iodide staining, indicating ZCOE is a “dead” stain for this organism. Staining of mammalian cells reveals complete internalization of ZCOE through endocytosis, as supported by colocalization with LysoTracker and late endosome markers. In all cases DSSN+ persists in the outer membranes, most likely due to its chemical structure more closely resembling a lipid bilayer.
Co-reporter:Lai Fan Lai ; John A. Love ; Alexander Sharenko ; Jessica E. Coughlin ; Vinay Gupta ; Sergei Tretiak ; Thuc-Quyen Nguyen ; Wai-Yeung Wong
Journal of the American Chemical Society 2014 Volume 136(Issue 15) pp:5591-5594
Publication Date(Web):March 24, 2014
DOI:10.1021/ja501711m
The molecule AT1, with two weakly conjugated chromophores, was designed, synthesized, and examined within the context of its film forming tendencies. While the addition of the second chromophore to the central core enables broadening of the absorption spectrum, this change is mostly apparent in films that are grown slowly. Grazing incidence X-ray scattering (GIWAXS) analysis indicates that these spectral characteristics correspond to an increase in solid state ordering. This information, in combination with differential scanning calorimetry, suggests that the overall molecular shape provides a kinetic barrier to crystallization. As a result, one finds the absence of molecular order when AT1 is combined with PC71BM in solution-cast blends. These findings highlight the importance of molecular topology when designing molecular components for solar cell devices.
Co-reporter:Ming Wang ; Hengbin Wang ; Takamichi Yokoyama ; Xiaofeng Liu ; Ye Huang ; Yuan Zhang ; Thuc-Quyen Nguyen ; Shinji Aramaki
Journal of the American Chemical Society 2014 Volume 136(Issue 36) pp:12576-12579
Publication Date(Web):August 14, 2014
DOI:10.1021/ja506785w
The regioregular narrow band gap (Eg ∼1.5 eV) conjugated polymer PIPCP was designed and synthesized. PIPCP contains a backbone comprised of CPDT-PT-IDT-PT repeat units (CPDT = cyclopentadithiophene, PT = pyridyl[2,1,3]thiadiazole, IDT = indacenodithiophene) and strictly organized PT orientations, such that the pyridyl N-atoms point toward the CPDT fragment. Comparison of PIPCP with the regiorandom counterpart PIPC-RA illustrates that the higher level of molecular order translates to higher power conversion efficiencies (PCEs) when incorporated into bulk heterojunction (BHJ) organic solar cells. Examination of thin films via absorption spectroscopy and grazing incidence wide-angle X-ray diffraction (GIWAXS) experiments provides evidence of higher order within thin films obtained by spin coating. Most significantly, we find that PIPCP:PC61BM blends yield devices with an open circuit voltage (Voc) of 0.86 V, while maintaining a PCE of ∼6%. Comparison against a wide range of analogous narrow band gap conjugated polymers reveals that this Voc value is particularly high for a BHJ system with band gaps in the 1.4–1.5 eV range thereby indicating a very low Eg – eVoc loss.
Co-reporter:Xiaofeng Liu ; Ben B. Y. Hsu ; Yanming Sun ; Cheng-Kang Mai ; Alan J. Heeger
Journal of the American Chemical Society 2014 Volume 136(Issue 46) pp:16144-16147
Publication Date(Web):October 27, 2014
DOI:10.1021/ja510088x
A series of narrow-band gap conjugated molecules with specific fluorine substitution patterns has been synthesized in order to study the effect of fluorination on bulk thermal stability. As the number of fluorine substituents on the backbone increase, one finds more thermally robust bulk structures both under inert and ambient conditions as well as an increase in phase transition temperatures in the solid state. When integrated into field-effect transistor devices, the molecule with the highest degree of fluorination shows a hole mobility of 0.15 cm2/V·s and a device thermal stability of >300 °C. Generally, the enhancement in thermal robustness of bulk organization and device performance correlates with the level of C–H for C–F substitution. These findings are relevant for the design of molecular semiconductors that can be introduced into optoelectronic devices to be operated under a wide range of conditions.
Co-reporter:Louis A. Perez, James T. Rogers, Michael A. Brady, Yanming Sun, Gregory C. Welch, Kristin Schmidt, Michael F. Toney, Hiroshi Jinnai, Alan J. Heeger, Michael L. Chabinyc, Guillermo C. Bazan, and Edward J. Kramer
Chemistry of Materials 2014 Volume 26(Issue 22) pp:6531
Publication Date(Web):October 15, 2014
DOI:10.1021/cm5031987
The use of small volumes of a high boiling point liquid as a “solvent additive” is a deposition processing method that has been implemented in most high/record performing polymer:fullerene-based bulk heterojunction (BHJ) solar cell devices. Recently, solvent additive processing has been employed in a solution processable small molecule (SPSM) BHJ system, viz., 5,5′-bis{(4-(7-hexylthiophen-2-yl)thiophen-2-yl)-[1,2,5]thiadiazolo[3,4-c]pyridine}3,3′-di-2-ethylhexylsilylene-2,2′-bithiophene:[6,6]-phenyl C71 butyric acid methyl ester (p-DTS(PTTh2)2:PC71BM), when a small amount, 0.25 v/v %, diiodooctane (DIO) was added to the casting solution, several key device metrics increased, leading to a high power conversion efficiency (PCE) of 6.7%. X-ray diffraction experiments show that the amount of additive added to the casting solution to make p-DTS(PTTh2)2:PC71BM thin films has several effects on the structure at multiple length scales: for example, the number and orientation of p-DTS(PTTh2)2 crystallites, different π–π stacking distances, and the nanoscale domain size. Additionally, we utilize energy filtered transmission electron microscopy (EFTEM), a technique that significantly enhances the contrast between p-DTS(PTTh2)2 and PC71BM in real space, to further verify the effect of increasing domain size as the additive concentration is increased. Tomographic reconstruction of the TEM micrographs provides a 3D representation of the BHJ structure. These studies show how domain size and tortuosity in all dimensions change due to solvent additive processing, and the overall finding is that the nanostructures of p-DTS(PTTh2)2 have enhanced connectivity when 0.25 v/v % DIO was used. Finally, we show evidence of solvent additive retention in p-DTS(PTTh2)2:PC71BM films when 1 v/v % DIO is used (but absent for 0.25%). This finding, in conjunction with the appearance of two populations of π–π stacking distances when 1 v/v % DIO is used, leads to the identification of one of the specific points of interaction between DIO and p-DTS(PTTh2)2.
Co-reporter:Jenny Du, Chelsea Catania, and Guillermo C. Bazan
Chemistry of Materials 2014 Volume 26(Issue 1) pp:686
Publication Date(Web):September 9, 2013
DOI:10.1021/cm401912j
Low efficiency of charge extraction (and conversely charge injection) across biotic–abiotic interfaces constitutes an obstacle to the integration of biological and electronic systems in high-performance bioelectronic devices. Advances in the promotion of charge transport across these typically nonconductive interfaces will have far-reaching implications in important applications such as alternative energy generation, bioelectrosynthesis, diagnostics, and environmental monitoring. This review highlights the use of synthetic materials to improve electrical interfacing between biological systems and electrodes, focusing specifically on whole cell bioelectrochemical systems. By taking advantage of a rich variety of materials chemistry and synthetic methodologies, significant improvements to the facilitation of charge transport across abiotic–biotic interfaces have been realized. The modifications of the bioelectronic interfaces presented herein include the use of organic small molecules, semiconducting and redox active polymers, inorganic nanoparticles, carbon nanotubes, graphene, hybrid organic–inorganic systems, and micro-/nanoelectrodes. However, design rules to guide material selection and choices regarding device architecture remain ambiguous. Establishment of a clearer understanding of bioelectronic charge transfer phenomena, their constituent pathways, and means of stimulating or selecting for different pathways is still work in progress. As such, great opportunities exist for materials scientists to contribute to these topics through design and implementation.Keywords: bioelectrochemical cells; bioelectronic interfaces; bioelectrosynthesis cells; electron transfer; microbial fuel cells;
Co-reporter:Paulina Gwozdzinska, Roza Pawlowska, Justyna Milczarek, Logan E. Garner, Alexander W. Thomas, Guillermo C. Bazan and Arkadiusz Chworos
Chemical Communications 2014 vol. 50(Issue 94) pp:14859-14861
Publication Date(Web):07 Oct 2014
DOI:10.1039/C4CC06478J
Conjugated phenylenevinylene oligoelectrolytes, which consist of a phenylenevinylene core equipped at each end with hydrophilic pendent groups, are shown to be good candidates for mammalian cell membrane staining. When used in the micromolar concentration range, they express low to moderate cell toxicity for selected regular and cancerous cell lines as tested for adherent and suspension cells.
Co-reporter:Nathan D. Kirchhofer, Xiaofen Chen, Enrico Marsili, James J. Sumner, Frederick W. Dahlquist and Guillermo C. Bazan
Physical Chemistry Chemical Physics 2014 vol. 16(Issue 38) pp:20436-20443
Publication Date(Web):25 Jul 2014
DOI:10.1039/C4CP03197K
Shewanella oneidensis MR-1 was cultivated on lactate with poised graphite electrode acceptors (E = +0.2 V vs. Ag/AgCl) in order to explore the basis for sustained increases in anodic current output following the addition of the lipid-intercalating conjugated oligoelectrolyte (COE), 4,4′-bis(4′-(N,N-bis(6′′-(N,N,N-trimethylammonium)hexyl)amino)-styryl)stilbene tetraiodide (DSSN+). Microbial cultures, which were spiked with DSSN+, exhibit a ∼2.2-fold increase in charge collected, a ∼3.1-fold increase in electrode colonization by S. oneidensis, and a ∼1.7-fold increase in coulombic efficiency from 51 ± 10% to an exceptional 84 ± 7% without obvious toxicity effects. Direct microbial biofilm voltammetry reveals that DSSN+ rapidly and sustainably increases cytochrome-based direct electron transfer and subsequently increases flavin-based mediated electron transfer. Control experiments indicate that DSSN+ does not contribute to the current in the absence of bacteria.
Co-reporter:Andreas Lorbach, Emily Maverick, Abel Carreras, Pere Alemany, Guang Wu, Miguel A. Garcia-Garibay and Guillermo C. Bazan
Physical Chemistry Chemical Physics 2014 vol. 16(Issue 25) pp:12980-12986
Publication Date(Web):22 May 2014
DOI:10.1039/C4CP01036A
A new fullerene structure was recently obtained from the reaction of a Lewis basic N-heterocyclic carbene (NHC) and the Lewis acidic C60. The molecular features of the zwitterionic adduct can be described as a molecular rotor with the fullerene cage acting as the rotator that spins about one distinct axis given by its C–C single bond linkage with the imidazolium heterocycle stator. A detailed structural analysis of the compound by means of single-crystal X-ray diffraction (XRD) revealed significant differences in the packing motifs of solvent-free and solvent-containing crystals. Variable temperature single-crystal XRD experiments (80 K ≤ T ≤ 480 K) carried out to investigate the rotational dynamics of the fullerene group in the higher quality solvent-free structure revealed atomic displacement parameters consistent with fast rotation of the highly symmetric fullerene in the solid state, whereas the imidazolium unit remains in a fixed position and therefore represents the stator. DFT and semiempirical calculations were applied to get insight into the profile of the rotational potential of the fullerene unit, particularly considering interactions with the neighboring molecules in the crystal lattice. The results indicate that the crystal environment leads to the presence of one lowest energy minimum that is connected to seven others that are slightly higher in energy through rotational barriers of approximately 1.5–2.5 kcal mol−1.
Co-reporter:Vishal B. Patil;Kuburat O. Saliu;Roxanne M. Jenkins;Edmund M. Carnahan;Edward J. Kramer;Glenn H. Fredrickson
Macromolecular Chemistry and Physics 2014 Volume 215( Issue 11) pp:1140-1145
Publication Date(Web):
DOI:10.1002/macp.201400139
Co-reporter:Xiaofen Chen;Dr. Xiaofeng Liu;Mark A. Burgers;Dr. Ye Huang ;Dr. Guillermo C. Bazan
Angewandte Chemie International Edition 2014 Volume 53( Issue 52) pp:
Publication Date(Web):
DOI:10.1002/anie.201411251
Co-reporter:Louis A. Perez, Peter Zalar, Lei Ying, Kristin Schmidt, Michael F. Toney, Thuc-Quyen Nguyen, Guillermo C. Bazan, and Edward J. Kramer
Macromolecules 2014 Volume 47(Issue 4) pp:1403-1410
Publication Date(Web):February 13, 2014
DOI:10.1021/ma4019679
A regioregular (RR) donor–acceptor conjugated copolymer based on cyclopenta[2,1-b:3,4-b′]dithiophene (CDT) and pyridal[2,1,3]thiadiazole (PT) structural units was prepared by using polymerization reactions involving reactants specifically designed to avoid random orientation of the asymmetric PT heterocycle along the copolymer backbone. Compared to its regioirregular (RI) counterpart, the RR polymer exhibits a 2 orders of magnitude increase in hole mobility from 0.005 to 0.6 cm2 V–1 s–1. To probe the reason for this difference in mobility, we examined the crystalline structure and its orientation in thin films of both copolymers as a function of depth via grazing incidence wide-angle X-ray scattering (GIWAXS). In the RI film, the π–π stacking direction of the crystallites is mainly perpendicular to the substrate normal (edge-on orientation) while in the RR film the crystallites adopt a mixed π–π stacking orientation in the center of the film as well as near the interface between the polymer and the dielectric layer. These results demonstrate that control of backbone regularity is another important design criterion to consider in the synthesis and optimization of new conjugated copolymers with asymmetric structural units.
Co-reporter:Xiaofen Chen;Dr. Xiaofeng Liu;Mark A. Burgers;Dr. Ye Huang ;Dr. Guillermo C. Bazan
Angewandte Chemie 2014 Volume 126( Issue 52) pp:14606-14609
Publication Date(Web):
DOI:10.1002/ange.201409208
Abstract
High-efficiency bulk heterojunction (BHJ) organic solar cells with power conversion efficiencies of more than 5 % can be fabricated using the green solvent 2-MeTHF. The active layers comprise a blend of a molecular semiconductor donor with intermediate dimensions (X2) and the soluble fullerene derivative [6,6]-phenyl-C61-butyricacidoctylester (PC61BC8). A switch of the processing solvent from chloroform to 2-MeTHF leads to no negative impacts on the morphology and charge-transport properties of optimally performing BHJ films. Examinations by absorption spectroscopy, atomic force microscopy, and grazing incidence wide-angle X-ray scattering reveal no significant modification of morphology. These results show that green solvents can be excellent alternatives for large-area printing of high-performance organic photovoltaics (OPVs) and thus open new opportunities for sustainable mass production of organic solar cells and other optoelectronic devices.
Co-reporter:Xiaofen Chen;Dr. Xiaofeng Liu;Mark A. Burgers;Dr. Ye Huang ;Dr. Guillermo C. Bazan
Angewandte Chemie International Edition 2014 Volume 53( Issue 52) pp:14378-14381
Publication Date(Web):
DOI:10.1002/anie.201409208
Abstract
High-efficiency bulk heterojunction (BHJ) organic solar cells with power conversion efficiencies of more than 5 % can be fabricated using the green solvent 2-MeTHF. The active layers comprise a blend of a molecular semiconductor donor with intermediate dimensions (X2) and the soluble fullerene derivative [6,6]-phenyl-C61-butyricacidoctylester (PC61BC8). A switch of the processing solvent from chloroform to 2-MeTHF leads to no negative impacts on the morphology and charge-transport properties of optimally performing BHJ films. Examinations by absorption spectroscopy, atomic force microscopy, and grazing incidence wide-angle X-ray scattering reveal no significant modification of morphology. These results show that green solvents can be excellent alternatives for large-area printing of high-performance organic photovoltaics (OPVs) and thus open new opportunities for sustainable mass production of organic solar cells and other optoelectronic devices.
Co-reporter:Xiaofen Chen;Dr. Xiaofeng Liu;Mark A. Burgers;Dr. Ye Huang ;Dr. Guillermo C. Bazan
Angewandte Chemie 2014 Volume 126( Issue 52) pp:
Publication Date(Web):
DOI:10.1002/ange.201411251
Co-reporter:Jessica E. Coughlin ; Andriy Zhugayevych ; Ronald C. Bakus ; II; Thomas S. van der Poll ; Gregory C. Welch ; Simon J. Teat ; Guillermo C. Bazan ;Sergei Tretiak
The Journal of Physical Chemistry C 2014 Volume 118(Issue 29) pp:15610-15623
Publication Date(Web):June 27, 2014
DOI:10.1021/jp506172a
Structural modules used for assembling molecular semiconductors have typically been chosen to give desirable optical and electronic properties. Growing evidence shows that chemical functionalities should be considered for controlling molecular shape, which is important for function because of its influence on polymer secondary structure, lattice arrangements in crystals, and crystallization tendencies. Using density functional theory (DFT) calculations, followed by a natural bond orbital (NBO) analysis, we examine eight molecular semiconductors with resolved single crystal X-ray structures to understand the features that dominate molecular conformations and ultimately develop practical rules that govern these preferences. All molecules can be described by a D′–A–D–A–D′ architecture and have a 4,4-dimethyl-4H-silolo[3,2-b:4,5-b′]dithiophene (DTS) donor (D) core unit, with [1,2,5]thiadiazolo[3,4-c]pyridine (PT), 5-fluorobenzo[c][1,2,5]thiadiazole (FBT), or benzo[1,2,5]thiadiazole (BT) electron acceptor (A) units, and either thiophene, 5-hexyl-2,2′-bithiophene, or benzofuran electron-donating end-caps (D′). The NBO analysis shows that the energy difference between the two alternative conformations, or rotamers, (ΔErot) is a delicate balance of multiple competing nonbonding interactions that are distributed among many atoms. These interactions include attractive “donor–acceptor” electron sharing, steric repulsion, and electrostatic stabilization or destabilization. A proper grouping of these interactions reveals two primary factors determining ΔErot. The first concerns heteroatoms adjacent to the bonds connecting the structural units, wherein the asymmetric distribution of π-electron density across the link joining the units results in stabilization of one of two rotamers. The second factor arises from electrostatic interactions between close-contact atoms, which may also shift the ΔErot of the two rotamers. When all these constituent interactions cooperate, the dihedral angle is “locked” in a planar conformation with a negligible population of alternative rotamers.
Co-reporter:Thomas S. van der Poll, Andriy Zhugayevych, Eli Chertkov, Ronald C. Bakus II, Jessica E. Coughlin, Simon J. Teat, Guillermo C. Bazan, and Sergei Tretiak
The Journal of Physical Chemistry Letters 2014 Volume 5(Issue 15) pp:2700-2704
Publication Date(Web):July 22, 2014
DOI:10.1021/jz5012675
Using ab initio calculations and classical molecular dynamics simulations coupled to complementary experimental characterization, four molecular semiconductors were investigated in vacuum, solution, and crystalline form. Independently, the molecules can be described as nearly isostructural, yet in crystalline form, two distinct crystal systems are observed with characteristic molecular geometries. The minor structural variations provide a platform to investigate the subtlety of simple substitutions, with particular focus on polymorphism and rotational isomerism. Resolved crystal structures offer an exact description of intermolecular ordering in the solid state. This enables evaluation of molecular binding energy in various crystallographic configurations to fully rationalize observed crystal packing on a basis of first-principle calculations of intermolecular interactions.Keywords: density functional theory; molecular mechanics; organic semiconductors; polymorphism; single crystals;
Co-reporter:Alexander W. Thomas, Logan E. Garner, Kelly P. Nevin, Trevor L. Woodard, Ashley E. Franks, Derek R. Lovley, James J. Sumner, Christian J. Sund and Guillermo C. Bazan
Energy & Environmental Science 2013 vol. 6(Issue 6) pp:1761-1765
Publication Date(Web):03 Apr 2013
DOI:10.1039/C3EE00071K
An amphiphilic conjugated oligoelectrolyte (COE) that spontaneously intercalates into lipid membranes enables Shewanella oneidensis to use a graphite electrode as the sole electron donor for succinate production. Current consumed in a poised electrochemical system by Shewanella with micromolar concentrations of COE correlates well with the succinate produced via fumarate reduction as determined by HPLC analysis. Confocal microscopy confirms incorporation of the COE into the microbes on the electrode surface. This work presents a unique strategy to induce favorable bioelectronic interactions for the production of reduced microbial metabolites.
Co-reporter:Huijie Hou;Xiaofen Chen;Alexer W. Thomas;Chelsea Catania;Nathan D. Kirchhofer;Logan E. Garner;Arum Han
Advanced Materials 2013 Volume 25( Issue 11) pp:1593-1597
Publication Date(Web):
DOI:10.1002/adma.201204271
Co-reporter:Louis A. Perez;Kang Wei Chou;John A. Love;Thomas S. van der Poll;Detlef-M. Smilgies;Thuc-Quyen Nguyen;Edward J. Kramer;Aram Amassian
Advanced Materials 2013 Volume 25( Issue 44) pp:6380-6384
Publication Date(Web):
DOI:10.1002/adma.201302389
Co-reporter:Wei Lin Leong;Gregory C. Welch;Jason Seifter;Jung Hwa Seo;Alan J. Heeger
Advanced Energy Materials 2013 Volume 3( Issue 3) pp:356-363
Publication Date(Web):
DOI:10.1002/aenm.201200631
Abstract
Two similar structural versions of a molecular donor, in which two terminal hexyl-substituted bithiophene units are connected to a central dithienosilole (DTS) through electron deficient thiadiazolopyridine (PT) units, and which differ only in the position of pyridyl N-atoms, were explored to study the interplay of crystallization and vertical phase segregation as a result of annealing. The donor materials exhibit greatly contrasting photovoltaic performance despite similarity in molecule structure. The difference in position of the pyridal N-atom which points away (distal configuration; compound 1) or towards (proximal configuration; compound 2) from the DTS core, modifies the aggregation/molecular packing in the solid state, resulting in differences in the phase segregation and formation of crystalline domains. A systematic study of the temperature dependence of photovoltaic performance reveals a parameter trade-off: as annealing temperature increases, higher donor crystallinity and ordering results, but increased donor segregation near the surface or decrease in electrode selectivity also occurs, resulting in increased interfacial recombination and hence reduction in open-circuit voltage (Voc). The higher crystalline nature of 2 is found to have a higher impact on cell performance despite a competing undesired effect at the donor/aluminum cathode interface, contributing to its superior performance to 1 when blended with [6,6]phenyl-C61-butyric acid methyl ester (PC61BM). Molecule 2 exhibits a performance increase of a factor of two after thermal annealing at 100 °C, achieving a power conversion efficiency of 5.7%.
Co-reporter:Paul A. Dalgarno ; Christopher A. Traina ; J. Carlos Penedo ; Guillermo C. Bazan ;Ifor D. W. Samuel
Journal of the American Chemical Society 2013 Volume 135(Issue 19) pp:7187-7193
Publication Date(Web):April 17, 2013
DOI:10.1021/ja311874f
The photophysical behavior of conjugated polymers used in modern optoelectronic devices is strongly influenced by their structural dynamics and conformational heterogeneity, both of which are dependent on solvent properties. Single molecule studies of these polymer systems embedded in a host matrix have proven to be very powerful to investigate the fundamental fluorescent properties. However, such studies lack the possibility of examining the relationship between conformational dynamics and photophysical response in solution, which is the phase from which films for devices are deposited. By developing a synthetic strategy to incorporate a biotin moiety as a surface attachment point at one end of a polyalkylthiophene, we immobilize it, enabling us to make the first single molecule fluorescence measurements of conjugated polymers for long periods of time in solution. We identify fluctuation patterns in the fluorescence signal that can be rationalized in terms of photobleaching and stochastic transitions to reversible dark states. Moreover, by using the advantages of solution-based imaging, we demonstrate that the addition of oxygen scavengers improves optical stability by significantly decreasing the photobleaching rates.
Co-reporter:Gregory C. Welch ; Ronald C. Bakus ; II; Simon J. Teat
Journal of the American Chemical Society 2013 Volume 135(Issue 6) pp:2298-2305
Publication Date(Web):January 8, 2013
DOI:10.1021/ja310694t
A comparison of two classes of small molecules relevant to the field of organic electronics is carried out at the molecular and supramolecular levels. First, two molecules that differ only in the position of a pyridyl N-atom within an acceptor fragment are compared and contrasted. X-ray investigation of single crystals reveals that positioning the pyridyl N-atoms proximal to the molecules center changes the molecular shape by bending the molecule into a banana shape. Second, we demonstrate that the banana shape of the molecule can be controlled by replacing a Si atom within the dithienosilole fragment with a C or Ge atom. Here, utilization of cyclopentadithiophene or dithienogermole as the internal electron-rich unit leads to a decrease or an increase in the bending of the conjugated backbone, respectively. Such molecular shape changes alter intermolecular packing and thus affect bulk properties, leading to large differences in the optical, thermal, and crystallization properties.
Co-reporter:Zachary B. Henson ; Yuan Zhang ; Thuc-Quyen Nguyen ; Jung Hwa Seo
Journal of the American Chemical Society 2013 Volume 135(Issue 11) pp:4163-4166
Publication Date(Web):March 5, 2013
DOI:10.1021/ja400140d
We report the design, synthesis, and optical and electronic properties of two novel narrow band gap conjugated polyelectrolytes (NBGCPEs) based on a poly[2,6-(4,4-bis-alkyl-4H-cyclopenta[2,1-b;3,4-b′]dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] donor/acceptor backbone. Comparison with the properties of the neutral precursor material shows that the ionic component in these cationic NBGCPEs leads to a red-shift in the absorption spectra and to a modification of the polymer electronic energy levels. Both the HOMO and the LUMO are lowered in energy, with the net effect being dependent on the choice of counterion, i.e. bromide vs tetrakis(1-imidazolyl)borate. Moreover, we unexpectedly find n-type transport in thin-film transistors, as opposed to the widely studied p-type transport in neutral systems with isoelectronic backbones. From these observations we conclude that introduction of ionic functionalities adjacent to semiconducting polymers that exhibit charge-transfer excitations offers unique opportunities for materials design.
Co-reporter:John A. Love;Christopher M. Proctor;Jianhua Liu;Christopher J. Takacs;Alexer Sharenko;Thomas S. van der Poll;Alan J. Heeger;Thuc-Quyen Nguyen
Advanced Functional Materials 2013 Volume 23( Issue 40) pp:5019-5026
Publication Date(Web):
DOI:10.1002/adfm.201300099
Morphological control over the bulk heterojunction (BHJ) microstructure of a high-efficiency small molecule photovoltaic system is demonstrated using both thermal treatment and solvent additive processing. Single crystal X-ray diffraction is utilized to understand molecular interactions in the solid state and the BHJ morphology is examined using bright field, high-resolution, and cross-section transmission electron microscopy techniques. Controlling the domain size, while maintaining good molecular order within the semiconducting donor material, is found to be crucial in achieving high performance and over 90% internal quantum efficiency exhibited under the optimized conditions.
Co-reporter:Bruno Grimm, Chad Risko, Jason D. Azoulay, Jean-Luc Brédas and Guillermo C. Bazan
Chemical Science 2013 vol. 4(Issue 4) pp:1807-1819
Publication Date(Web):06 Feb 2013
DOI:10.1039/C3SC22188A
We discuss donor–acceptor conjugated polymers where the acceptor moieties are orthogonal to the donor-based backbone direction through the synthesis and study of a new class of materials (including six oligomers and three polymers) based on 4H-cyclopentadithiophene (CPDT) with an imine functionality introduced at the CPDT bridgehead position. Absorption spectroscopy provides information on the influence of structure on the optical properties. We paid special attention to the energies and oscillator strengths of the low-energy transitions and how they correlate with chain length. When the orthogonally conjugated materials are compared to a more traditional polymer, where the donor and acceptor fragments are in series along the backbone direction, fundamental differences in the optical properties are observed. Quantum-mechanical studies of the geometric structure, electronic structure, and excited-state vertical transitions using density functional theory unravel the interplay of structural design and resulting optoelectronic properties. Our findings underline that the magnitude and orientation relative to the backbone long axis of the transition dipole moment is key in designing narrow optical-gap materials with large absorption cross-sections and oscillator strengths.
Co-reporter:Zachary B. Henson, Peter Zalar, Xiaofen Chen, Gregory C. Welch, Thuc-Quyen Nguyen and Guillermo C. Bazan
Journal of Materials Chemistry A 2013 vol. 1(Issue 37) pp:11117-11120
Publication Date(Web):19 Jul 2013
DOI:10.1039/C3TA12690K
We present the design and synthesis of molecular organic semiconductors enabling processing from environmentally friendly solvents, including ethyl acetate. The structural changes employed do not adversely influence the attractive optical or electronic properties of the parent chromophore. Thin film transistors demonstrate the semiconducting ability of the new structures when processed from ethyl acetate.
Co-reporter:Jenny Du, Alexander W. Thomas, Xiaofen Chen, Logan E. Garner, Carol A. Vandenberg and Guillermo C. Bazan
Chemical Communications 2013 vol. 49(Issue 83) pp:9624-9626
Publication Date(Web):02 Sep 2013
DOI:10.1039/C3CC45094E
Variation in conjugated oligoelectrolyte (COE) repeat units is shown to affect the rate of COE insertion into mammalian membrane patches and membrane patch stabilities. These findings suggest that it is possible to find COE structures that do not destroy membranes while at the same time allow for more facile transmembrane movement of ions/substrates.
Co-reporter:Wen Wen, Lei Ying, Ben B. Y. Hsu, Yuan Zhang, Thuc-Quyen Nguyen and Guillermo C. Bazan
Chemical Communications 2013 vol. 49(Issue 65) pp:7192-7194
Publication Date(Web):28 May 2013
DOI:10.1039/C3CC43229G
Regioregular conjugated polymers containing alternating pyridyl[2,1,3]thiadiazole (PT) and indacenodithiophene (IDT) structural units were synthesized. In these copolymers, the pyridyl nitrogen atoms on PT are precisely arranged along the backbone so that each one has an adjacent proximal and an adjacent distal counterpart across the two IDT flanking units. We find that despite the absence of obvious differences in orbital energy levels and optical bandgap, the regioregular materials exhibit larger charge carrier mobilities, as determined by using field effect transistor devices, and can yield higher solar cell power conversion efficiencies when mixed with fullerenes in bulk heterojunction active layers.
Co-reporter:Victor Bochuan Wang, Jenny Du, Xiaofen Chen, Alexander W. Thomas, Nathan D. Kirchhofer, Logan E. Garner, Myat Thiri Maw, Wee Han Poh, Jamie Hinks, Stefan Wuertz, Staffan Kjelleberg, Qichun Zhang, Joachim Say Chye Loo and Guillermo C. Bazan
Physical Chemistry Chemical Physics 2013 vol. 15(Issue 16) pp:5867-5872
Publication Date(Web):19 Feb 2013
DOI:10.1039/C3CP50437A
It is important to tailor biotic–abiotic interfaces in order to maximize the utility of bioelectronic devices such as microbial fuel cells (MFCs), electrochemical sensors and bioelectrosynthetic systems. The efficiency of electron-equivalent extraction (or injection) across such biotic–abiotic interfaces is dependent on the choice of the microbe and the conductive electrode material. In this contribution, we show that spontaneous intercalation of a conjugated oligoelectrolyte, namely 4,4′-bis(4′-(N,N-bis(6′′-(N,N,N-trimethylammonium)hexyl)amino)-styryl)stilbene tetraiodide (DSSN+), into the membranes of Escherichia coli leads to an increase in current generation in MFCs containing carbon-based electrodes. A combination of scanning electron microscopy (SEM) and confocal microscopy was employed to confirm the incorporation of DSSN+ into the cell membrane and biofilm formation atop carbon felt electrodes. Current collection was enhanced by more than 300% with addition of this conjugated oligoelectrolyte. The effect of DSSN+ concentration on electrical output was also investigated. Higher concentrations, up to 25 μM, lead to an overall increase in the number of charge equivalents transferred to the charge-collecting electrode, providing evidence in support of the central role of the synthetic system in improving device performance.
Co-reporter:Dr. Cheng-Kang Mai;Dr. Huiqiong Zhou;Dr. Yuan Zhang;Zachary B. Henson;Dr. Thuc-Quyen Nguyen;Dr. Alan J. Heeger ;Dr. Guillermo C. Bazan
Angewandte Chemie 2013 Volume 125( Issue 49) pp:13112-13116
Publication Date(Web):
DOI:10.1002/ange.201307667
Co-reporter:Dr. Cheng-Kang Mai;Dr. Huiqiong Zhou;Dr. Yuan Zhang;Zachary B. Henson;Dr. Thuc-Quyen Nguyen;Dr. Alan J. Heeger ;Dr. Guillermo C. Bazan
Angewandte Chemie International Edition 2013 Volume 52( Issue 49) pp:12874-12878
Publication Date(Web):
DOI:10.1002/anie.201307667
Co-reporter:Andriy Zhugayevych, Olena Postupna, Ronald C. Bakus II, Gregory C. Welch, Guillermo C. Bazan, and Sergei Tretiak
The Journal of Physical Chemistry C 2013 Volume 117(Issue 10) pp:4920-4930
Publication Date(Web):February 17, 2013
DOI:10.1021/jp310855p
Using ab initio methods we examine the molecular and solid-state electronic properties of a recently synthesized small-molecule donor, p-DTS(PTTh2)2, which belongs to the dithienosilole-pyridylthiadiazole family of chromophores. In combination with the PC70BM acceptor, p-DTS(PTTh2)2 can be used to fabricate high-efficiency bulk heterojunction organic solar cells. A precise picture of molecular structure and interchromophore packing is provided via a single-crystal X-ray diffraction study; such details cannot be easily obtained with donor materials based on conjugated polymers. In first-principles approaches we are limited to a single-crystallite scale. At this scale, according to our investigation, the principal properties responsible for the high efficiency are strong low-energy light absorption by individual molecules, large exciton diffusion length, and fast disorder-resistant hole transport along π-stacks in the crystallite. The calculated exciton diffusion length is substantially larger than the average crystallite size in previously characterized device active layers, and the calculated hole mobility is 2 orders of magnitude higher than the measured device-scale mobility, meaning that the power conversion “losses” on a single-crystallite scale are minimal.
Co-reporter:Jason D. Azoulay, Zachary A. Koretz, Bryan M. Wong, and Guillermo C. Bazan
Macromolecules 2013 Volume 46(Issue 4) pp:1337-1342
Publication Date(Web):February 7, 2013
DOI:10.1021/ma302569u
Bridgehead imine substituted cyclopentadithiophene structural units offer the opportunity to modify the electronic properties, in particular, the HOMO–LUMO energy levels of donor–acceptor polymers with unprecedented precision. Utilizing a common synthetic pathway, copolymers with high average molecular weights, a variety of functionality, and properties suitable for solar cell incorporation can be generated. The fabrication of organic photovoltaic devices with these new materials is demonstrated.
Co-reporter:Logan E. Garner, Alexander W. Thomas, James J. Sumner, Steven P. Harvey and Guillermo C. Bazan
Energy & Environmental Science 2012 vol. 5(Issue 11) pp:9449-9452
Publication Date(Web):04 Sep 2012
DOI:10.1039/C2EE22839D
The conjugated oligoelectrolyte 4,4′-bis(4′-(N,N-bis(6′′-(N,N,N-trimethylammonium)hexyl)amino)-styryl)stilbene tetraiodide (DSSN+) has been employed to improve the performance of wastewater microbial fuel cells (MFCs) with respect to current generation and organic contaminant removal. The best performance was afforded by biocathode type MFCs run in the presence of DSSN+. Laser scanning confocal microscopy confirmed cellular uptake of DSSN+ in the biofilms.
Co-reporter:Yuan Zhang;Peter Zalar;Chunki Kim;Samuel Collins;Thuc-Quyen Nguyen
Advanced Materials 2012 Volume 24( Issue 31) pp:4255-4260
Publication Date(Web):
DOI:10.1002/adma.201201248
Co-reporter:Xiaofeng Liu;Wen Wen
Advanced Materials 2012 Volume 24( Issue 33) pp:4505-4510
Publication Date(Web):
DOI:10.1002/adma.201201567
Co-reporter:Sooncheol Kwon;Jin Kuen Park;Geunjin Kim;Jaemin Kong;Kwanghee Lee
Advanced Energy Materials 2012 Volume 2( Issue 12) pp:1420-1424
Publication Date(Web):
DOI:10.1002/aenm.201200311
Co-reporter:Sooncheol Kwon;Jin Kuen Park;Geunjin Kim;Jaemin Kong;Kwanghee Lee
Advanced Energy Materials 2012 Volume 2( Issue 12) pp:
Publication Date(Web):
DOI:10.1002/aenm.201290057
Co-reporter:Hsin-Rong Tseng, Lei Ying, Ben B. Y. Hsu, Louis A. Perez, Christopher J. Takacs, Guillermo C. Bazan, and Alan J. Heeger
Nano Letters 2012 Volume 12(Issue 12) pp:6353-6357
Publication Date(Web):November 21, 2012
DOI:10.1021/nl303612z
Field-effect transistors fabricated from semiconducting conjugated polymers are candidates for flexible and low-cost electronic applications. Here, we demonstrate that the mobility of high molecular weight (300 kDa) regioregular, poly[4-(4,4-dihexadecyl-4H-cyclopenta[1,2-b:5,4-b′]dithiophen-2-yl)-alt-[1,2,5]thiadiazolo[3,4-c]pyridine] can be significantly improved by introducing long-range orientation of the polymer chains. By annealing for short periods, hole mobilities of 6.7 cm2/(V s) have been demonstrated. The transport is anisotropic, with a higher mobility (approximately 6:1) parallel to the polymer backbone than that perpendicular to the polymer backbone.
Co-reporter:Christopher J. Takacs ; Yanming Sun ; Gregory C. Welch ; Louis A. Perez ; Xiaofeng Liu ; Wen Wen ; Guillermo C. Bazan ;Alan J. Heeger
Journal of the American Chemical Society 2012 Volume 134(Issue 40) pp:16597-16606
Publication Date(Web):September 6, 2012
DOI:10.1021/ja3050713
We examine the correlations of the dipole moment and conformational stability to the self-assembly and solar cell performance within a series of isomorphic, solution-processable molecules. These charge-transfer chromophores are described by a D1-A-D-A-D1 structure comprising electron-rich 2-hexylbithiophene and 3,3′-di-2-ethylhexylsilylene-2,2′-bithiophene moieties as the donor units D1 and D, respectively. The building blocks 2,1,3-benzothiadiazole (BT) and [1,2,5]thiadiazolo[3,4-c]pyridine (PT) were used as the electron-deficient acceptor units A. Using a combination of UV–visible spectroscopy, field-effect transistors, solar cell devices, grazing incident wide-angle X-ray scattering, and transmission electron microscopy, three PT-containing compounds (1–3) with varying regiochemistry and symmetry, together with the BT-based compound 5,5′-bis{(4-(7-hexylthiophen-2-yl)thiophen-2-yl)-[1,2,5]thiadiazolobenzene}-3,3′-di-2-ethylhexylsilylene-2,2′-bithiophene (4), are compared and contrasted in solution, in thin films, and as blends with the electron acceptor [6,6]-phenyl-C70-butyric acid methyl ester. The molecules with symmetric orientations of the PT acceptor, 1 and 2, yield highly ordered blended thin films. The best films, processed with the solvent additive 1,8-diiodooctane, show donor “crystallite” length scales on the order of 15–35 nm and photovoltaic power conversion efficiencies (PCEs) of 7.0 and 5.6%, respectively. Compound 3, with an unsymmetrical orientation of PT heterocycles, shows subtle differences in the crystallization behavior and a best PCE of 3.2%. In contrast, blends of the BT-containing donor 4 are highly disordered and give PCEs below 0.2%. We speculate that the differences in self-assembly arise from the strong influence of the BT acceptor and its orientation on the net dipole moment and geometric description of the chromophore.
Co-reporter:Xiaofeng Liu ; Yanming Sun ; Louis A. Perez ; Wen Wen ; Michael F. Toney ; Alan J. Heeger
Journal of the American Chemical Society 2012 Volume 134(Issue 51) pp:20609-20612
Publication Date(Web):December 7, 2012
DOI:10.1021/ja310483w
The influence of extending the molecular length of donor–acceptor chromophores on properties relevant to organic optoelectronic devices has been studied by using two new narrow-band-gap systems. Most significantly, we find that the higher molecular weight systems exhibit higher thermal stabilities (beyond 200 °C) when introduced into field effect transistor devices. It is also possible to fabricate bulk heterojunction solar cells using PC61BM with power conversion efficiencies >6%. These high values are not heavily influenced by the blend composition and are achieved without the influence of solvent additives or postdeposition thermal annealing.
Co-reporter:James T. Rogers ; Kristin Schmidt ; Michael F. Toney ; Guillermo C. Bazan ;Edward J. Kramer
Journal of the American Chemical Society 2012 Volume 134(Issue 6) pp:2884-2887
Publication Date(Web):January 25, 2012
DOI:10.1021/ja2104747
Solution deposition using high-boiling-point additives such as octanedithiol (ODT) provides a simple and widely used fabrication option for improving the power conversion efficiencies of solar cells composed of narrow-band-gap conjugated polymer donor/fullerene acceptor blends. Previous examination of the resulting device active layers has shown that the use of additives influences the degree of phase segregation within the bulk heterojunction (BHJ) blend and also improves ordering within the polymeric domains. In this work, in situ grazing-incidence wide-angle X-ray scattering as a function of time was used to explore the dynamics of the BHJ evolution. These studies showed that a small percentage of ODT in chlorobenzene (CB) induced the nucleation of polymeric crystallites within 2 min of deposition, increased the orientational order of specific polymorphs, and promoted further crystallite nucleation over a period longer than 40 min after casting. Similar structural changes did not occur when the same BHJ blend was cast from pure CB.
Co-reporter:Zachary B. Henson ; Gregory C. Welch ; Thomas van der Poll
Journal of the American Chemical Society 2012 Volume 134(Issue 8) pp:3766-3779
Publication Date(Web):January 27, 2012
DOI:10.1021/ja209331y
π-Conjugated materials containing pyridal[2,1,3]thiadiazole (PT) units have recently achieved record power conversion efficiencies of 6.7% in solution-processed, molecular bulk-heterojunction (BHJ) organic photovoltaics. Recognizing the importance of this new class of molecular systems and with the aim of establishing a more concrete path forward to predict improvements in desirable solid-state properties, we set out to systematically alter the molecular framework and evaluate structure–property relationships. Thus, the synthesis and properties of 13 structurally related D1-PT-D2-PT-D1 compounds, where D represents a relatively electron-rich aromatic segment compared to PT, are provided. Physical properties were examined using a combination of absorption spectroscopy, cyclic voltammetry, thermal gravimetric analysis, differential scanning calorimetry, and solubility analysis. Changes to end-capping D1 units allowed for fine control over electronic energy levels both in solution and in the bulk. Substitution of different alkyl chains on D2 gives rise to controllable melting and crystallization temperatures and tailored solubility. Alterations to the core donor D2 lead to readily identifiable changes in all properties studied. Finally, the regiochemistry of the pyridal N-atom in the PT heterocycle was investigated. The tailoring of structures via subtle structural modifications in the presented molecular series highlights the simplicity of accessing this chromophore architecture. Examination of the resulting materials properties relevant for device fabrication sets forth which can be readily predicted by consideration of molecular structure and which lack a systematic understanding. Guidelines can be proposed for the design of new molecular frameworks with the possibility of outperforming the current state of the art OPV performance.
Co-reporter:Xing Guan;Kai Zhang;Fei Huang;Yong Cao
Advanced Functional Materials 2012 Volume 22( Issue 13) pp:2846-2854
Publication Date(Web):
DOI:10.1002/adfm.201200199
Abstract
A series of amino N-oxide functionalized polyfluorene homopolymers and copolymers (PNOs) are synthesized by oxidizing their amino functionalized precursor polymers (PNs) with hydrogen peroxide. Excellent solubility in polar solvents and good electron injection from high work-function metals make PNOs good candidates for interfacial modification of solution processed multilayer polymer light-emitting diodes (PLEDs) and polymer solar cells (PSCs). Both PNOs and PNs are used as cathode interlayers in PLEDs and PSCs. It is found that the resulting devices show much better performance than devices based on a bare Al cathode. The effect of side chain and main chain variations on the device performance is investigated. PNOs/Al cathode devices exhibit better performance than PNs/Al cathode devices. Moreover, devices incorporating polymers with para-linkage of pyridinyl moieties exhibit better performance than those using polymers with meta-linked counterparts. With a poly[(2,7-(9,9-bis(6-(N,N-diethylamino)-hexyl N-oxide)fluorene))-alt-(2,5-pyridinyl)] (PF6NO25Py) cathode interlayer, the resulting device exhibits a luminance efficiency of 16.9 cd A−1 and a power conversion efficiency of 6.9% for PLEDs and PSCs, respectively. These results indicate that PNOs are promising new cathode interlayers for modifying a range of optoelectronic devices.
Co-reporter:Wei Lin Leong, Gregory C. Welch, Loren G. Kaake, Christopher J. Takacs, Yanming Sun, Guillermo C. Bazan and Alan J. Heeger
Chemical Science 2012 vol. 3(Issue 6) pp:2103-2109
Publication Date(Web):26 Mar 2012
DOI:10.1039/C2SC20157G
The final step in the preparation of ppp-DTS(PTTh222)222 involves end capping of the PT-DTS-PT core with 2-hexylbithiophene units via a microwave assisted Stille cross coupling reaction. Methyl transfer (instead of 2-hexylbithiophene transfer) can occur leading to the formation of (MePT)DTS(PTTh22). Although (MePT)DTS(PTTh22) is difficult to separate from the ppp-DTS(PTTh222)222 product via column chromatography, it is readily extracted using hexanes solvent to give absolute ppp-DTS(PTTh222)222. Trace impurities of (MePT)DTS(PTTh22) in BHJ solar cells fabricated from synthesis batches of ppp-DTS(PTTh222)222 significantly influence the photovoltaic properties, causing a ∼50% reduction in efficiency and affecting all of the relevant device parameters (Jsc, Voc and FF). From a broader perspective, despite molecular design, the suitability of a material for efficient devices is often only determined by trial and error in the device processing laboratory. As shown by the data presented in this publication, promising materials found to be unsuitable for device applications may suffer from highly dilute impurities that act to increase carrier recombination.
Co-reporter:Yeong Don Park, Jin Kuen Park, Wi Hyoung Lee, Boseok Kang, Kilwon Cho and Guillermo C. Bazan
Journal of Materials Chemistry A 2012 vol. 22(Issue 23) pp:11462-11465
Publication Date(Web):24 Apr 2012
DOI:10.1039/C2JM31183F
By dipping into hexane, it is possible to efficiently eliminate the low MW component and also improve the molecular ordering of a conjugated polymer thin film. These changes improve the performance of field-effect transistors. The correlation between the nanoscalar structural features and the electrical properties enables us to determine both the appropriate dipping time and how the low MW component influences electronic properties.
Co-reporter:Peter Zalar;Zachary B. Henson;Dr. Gregory C. Welch;Dr. Guillermo C. Bazan;Dr. Thuc-Quyen Nguyen
Angewandte Chemie 2012 Volume 124( Issue 30) pp:7613-7616
Publication Date(Web):
DOI:10.1002/ange.201202570
Co-reporter:Aidee Duarte;Morris Slutsky; Grady Hanrahan;Dr. Charlene M. Mello; Guillermo C. Bazan
Chemistry - A European Journal 2012 Volume 18( Issue 3) pp:756-759
Publication Date(Web):
DOI:10.1002/chem.201103237
Co-reporter:Aidee Duarte;Morris Slutsky; Grady Hanrahan;Dr. Charlene M. Mello; Guillermo C. Bazan
Chemistry - A European Journal 2012 Volume 18( Issue 3) pp:
Publication Date(Web):
DOI:10.1002/chem.201290005
Co-reporter:Peter Zalar;Zachary B. Henson;Dr. Gregory C. Welch;Dr. Guillermo C. Bazan;Dr. Thuc-Quyen Nguyen
Angewandte Chemie International Edition 2012 Volume 51( Issue 30) pp:7495-7498
Publication Date(Web):
DOI:10.1002/anie.201202570
Co-reporter:Jason D. Azoulay, Haiyang Gao, Zachary A. Koretz, Gerald Kehr, Gerhard Erker, Fumihiko Shimizu, Griselda B. Galland, and Guillermo C. Bazan
Macromolecules 2012 Volume 45(Issue 11) pp:4487-4493
Publication Date(Web):May 17, 2012
DOI:10.1021/ma300504j
13C NMR spectroscopy is used to characterize the microstructure of polypropylene (PP) obtained using a nickel α-keto-β-diimine initiator activated with methylaluminoxane (MAO) at different reaction temperatures (Trxn). The product prepared at −20 °C has structural features that resemble an ethylene-propylene copolymer. We find that the main sequences present in this sample arise as a result of normal 1,2-insertion and that propylene sequences are predominantly isotactic (m = 88%, mmmm = 63%). There is also evidence of ethylene-like sequences as a result of 3,1-enchainment, and from 2,1-insertion. A reduction in Trxn to −60 °C results in a polymer that has undetectable regioirregularities and is highly isotactic (m = 93%, mmmm = 85%). Moreover, the application of stereo propagation models gives indication that the isospecificity is a result of enantiomorphic site control.
Co-reporter:Andrea Gutacker, Chi-Yen Lin, Lei Ying, Thuc-Quyen Nguyen, Ullrich Scherf, and Guillermo C. Bazan
Macromolecules 2012 Volume 45(Issue 11) pp:4441-4446
Publication Date(Web):May 31, 2012
DOI:10.1021/ma202738t
All-conjugated “rod–rod” diblock copolymers are an emerging class of polymeric materials of considerable interest for applications in chemical and biological sensors or as components for optoelectronic devices. Here, we report a novel cationic diblock copolymer containing a neutral polyalkylfluorene block covalently bound to a polar polyfluorene counterpart—poly[9,9-bis(6-trimethylammoniumhexyl)-2,7-fluorene]-b-poly(3-hexyl-2,5-thiophene) (PF6NBr-b-PF8)—which was synthesized in a sequential Suzuki–Miyaura polymerization and was made ionic with trimethylamine in a subsequent quaternization step. The optical properties of this material were investigated by UV/vis and photoluminescence spectroscopies in three different solvents: methanol, THF and THF/methanol 1:1. Atomic force microscopic (AFM) imaging experiments provided evidence for solvent-induced aggregation. The formation of vesicles and spherical particles is observed in layers from THF and methanolic solution.
Co-reporter:David H. Auston;Glenn H. Fredrickson;Craig J. Hawker;Daniel E. Morse;Tresa M. Pollock;Ram Seshadri
Advanced Materials 2011 Volume 23( Issue 20) pp:2256-2259
Publication Date(Web):
DOI:10.1002/adma.201101196
Co-reporter:Yeong Don Park;Jin Kuen Park;Jung Hwa Seo;Jonathan D. Yuen;Wi Hyoung Lee;Kilwon Cho
Advanced Energy Materials 2011 Volume 1( Issue 1) pp:63-67
Publication Date(Web):
DOI:10.1002/aenm.201000005
Co-reporter:Julia H. Ortony ; Tirtha Chatterjee +; Logan E. Garner ; Arkadiusz Chworos ; Alexander Mikhailovsky ; Edward J. Kramer
Journal of the American Chemical Society 2011 Volume 133(Issue 21) pp:8380-8387
Publication Date(Web):May 6, 2011
DOI:10.1021/ja202776b
Conjugated oligoelectrolytes are of emerging technological interest due to their recent function in the fabrication of optoelectronic devices, application in biosensors, and as species that facilitate transmembrane charge migration. Solubility in aqueous, or highly polar, solvents is important for many of these applications; however, there are few studies on how the self-assembly of conjugated oligoelectrolytes into multichromophore species influences linear and nonlinear optical properties. Here, we examine 1,4-bis(4′-(N,N-bis(6′′-(N,N,N-trimethylammonium)hexyl)amino)-styryl)benzene tetraiodide (DSBNI) in water, a conjugated oligoelectrolyte based on the distyrylbenzene framework. We find that DSBNI aggregation leads to increased fluorescence lifetimes, coupled with hypsochromic shifts, and larger two-photon absorption cross sections. Liquid atomic force microscopy (AFM) and cryogenic transmission electron microscopy (cryo-TEM) were used to image DSBNI aggregates and to confirm that the planar molecules stack to form nanocylinders above a critical aggregation concentration. Finally, small-angle neutron scattering (SANS) was used to quantify the aggregate dimensions in situ. Comparison of the results highlights that the hydrophilic mica surface used to image via liquid AFM and the high concentrations required for cryo-TEM facilitate the propagation of the cylinders into long fibers. SANS experiments are consistent with equivalent molecular packing geometry but lower aspect ratios. It is therefore possible to understand the evolution of optical properties as a function of concentration and aggregation and the general geometric features of the resulting supramolecular structures.
Co-reporter:Jung Hwa Seo ; Andrea Gutacker ; Yanming Sun ; Hongbin Wu ; Fei Huang ; Yong Cao ; Ullrich Scherf ; Alan J. Heeger
Journal of the American Chemical Society 2011 Volume 133(Issue 22) pp:8416-8419
Publication Date(Web):May 10, 2011
DOI:10.1021/ja2037673
The power conversion efficiencies of bulk heterojunction (BHJ) solar cells can be increased from 5 to 6.5% by incorporating an ultrathin conjugated polyelectrolyte (CPE) layer between the active layer and the metal cathode. Poly[N-9′′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT) and [6,6]-phenyl C71 butyric acid methyl ester (PC71BM) were chosen for the photoactive layer. CPEs with cationic polythiophenes, in both homopolymer and block copolymer configurations, were used to improve the electronic characteristics. The significant improvement in device performance and the simplicity of fabrication by solution processing suggest a promising and practical pathway for improving polymer solar cells with high efficiencies.
Co-reporter:Peter Zalar ; Daniel Kamkar ; Rajesh Naik ; Fahima Ouchen ; James G. Grote ; Guillermo C. Bazan ;Thuc-Quyen Nguyen
Journal of the American Chemical Society 2011 Volume 133(Issue 29) pp:11010-11013
Publication Date(Web):June 9, 2011
DOI:10.1021/ja201868d
Introduction of a DNA interlayer adjacent to an Al cathode in a polymer light-emitting diode leads to lower turn-on voltages, higher luminance efficiencies, and characteristics comparable to those observed using a Ba electrode. The DNA serves to improve electron injection and also functions as a hole-blocking layer. The temporal characteristics of the devices are consistent with an interfacial dipole layer adjacent to the electrode being responsible for the reduction of the electron injection barrier.
Co-reporter:Christopher A. Traina ; Ronald C. Bakus II
Journal of the American Chemical Society 2011 Volume 133(Issue 32) pp:12600-12607
Publication Date(Web):July 13, 2011
DOI:10.1021/ja202877q
Water-soluble conjugated polymers with controlled molecular weight characteristics, absence of ionic groups, high emission quantum yields, and end groups capable of selective reactions of wide scope are desirable for improving their performance in various applications and, in particular, fluorescent biosensor schemes. The synthesis of such a structure is described herein. 2-Bromo-7-iodofluorene with octakis(ethylene glycol) monomethyl ether chains at the 9,9′-positions, i.e., compound 4, was prepared as the reactive premonomer. A high-yielding synthesis of the organometallic initiator (dppe)Ni(Ph)Br (dppe = 1,2-bis(diphenylphosphino)ethane) was designed and implemented, and the resulting product was characterized by single-crystal X-ray diffraction techniques. Polymerization of 4 by (dppe)Ni(Ph)Br can be carried out in less than 30 s, affording excellent control over the average molecular weight and polydispersity of the product. Quenching of the polymerization with [2-(trimethylsilyl)ethynyl]magnesium bromide yields silylacetylene-terminated water-soluble poly(fluorene) with a photoluminescence quantum efficiency of 80%. Desilylation, followed by copper-catalyzed azide–alkyne cycloaddition reaction, yields a straightforward route to introduce a wide range of specific end group functionalities. Biotin was used as an example. The resulting biotinylated conjugated polymer binds to streptavidin and acts as a light-harvesting chromophore to optically amplify the emission of Alexa Fluor-488 chromophores bound onto the streptavidin. Furthermore, the biotin end group makes it possible to bind the polymer onto streptavidin-functionalized cross-linked agarose beads and thereby incorporate a large number of optically active segments.
Co-reporter:Huaping Li ; Chad Risko ; Jung Hwa Seo ; Casey Campbell ; Guang Wu ; Jean-Luc Brédas
Journal of the American Chemical Society 2011 Volume 133(Issue 32) pp:12410-12413
Publication Date(Web):July 17, 2011
DOI:10.1021/ja204974m
The reaction between a bulky N-heterocylic carbene (NHC) and C60 leads to the formation of a thermally stable zwitterionic Lewis acid–base adduct that is connected via a C–C single bond. Low-energy absorption bands with weak oscillator strengths similar to those of n-doped fullerenes were observed for the product, consistent with a net transfer of electron density to the C60 core. Corroborating information was obtained using UV photoelectron spectroscopy, which revealed that the adduct has an ionization potential ∼1.5 eV lower than that of C60. Density functional theory calculations showed that the C–C bond is polarized, with a total charge of +0.84e located on the NHC framework and −0.84e delocalized on the C60 cage. The combination of reactivity, characterization, and theoretical studies demonstrates that fullerenes can behave as Lewis acids that react with C-based Lewis bases and that the overall process describes n-doping via C–C bond formation.
Co-reporter:Gregory C. Welch and Guillermo C. Bazan
Journal of the American Chemical Society 2011 133(12) pp: 4632-4644
Publication Date(Web):March 4, 2011
DOI:10.1021/ja110968m
We report on the interaction of Lewis acids with narrow band gap conjugated copolymers containing donor and acceptor units. Examination of the widely used poly[(4,4-bis(2-ethylhexyl)cyclopenta-[2,1-b:3,4-b′]dithiophene)-2,6-(diyl-alt-benzo[2,1,3]thiadiazole)-4,7-diyl] (1) shows weaker binding with B(C6F5)3 when compared with a small molecule that contains a cyclopenta-[2,1-b:3,4-b′]dithiophene (CDT) unit flanked by two benzo[2,1,3]thiadiazole (BT) fragments. Studies on model compounds representative of 1, together with a comparison between B(C6F5)3 and BBr3, indicate that the propensity for Lewis acid coordination is decreased because of steric encumbrance surrounding the BT nitrogen sites. These observations led to the design of chromophores that incorporate an acceptor unit with a more basic nitrogen site, namely pyridal[2,1,3]thiadiazole (PT). That this strategy leads to a stronger B−N interaction was demonstrated through the examination of the reaction of B(C6F5)3 with two small molecules bis(4,4-bis(hexyl)-4H-cyclopenta[2,1-b;3,4-b′]dithiophene)-4,7-pyridal[2,1,3]thiadiazole (8) and bis{2-thienyl-(4,4-bis(hexyl)-4H-cyclopenta[2,1-b;3,4-b′]dithiophene)}-4,7-pyridal[2,1,3]thiadiazole (9) and two polymer systems (poly[(4,4-bis(2-ethylhexyl)cyclopenta-[2,1-b:3,4-b′]dithiophene)-2,6-diyl-alt-([1,2,5]thiadiazolo[3,4-c]pyridine)-4,7-diyl] (10) and poly[(4,4-bis(2-ethylhexyl)cyclopenta-[2,1-b:3,4-b′]dithiophene)-2,6-diyl-alt-(4′,7′-bis(2-thienyl)-[1,2,5]thiadiazolo[3,4-c]pyridine)-5,5-diyl] (11). From a materials perspective, it is worth pointing out that through the binding of B(C6F5)3, new NIR-absorbing polymers can be generated with band gaps from 1.31 to 0.89 eV. A combination of studies involving ultraviolet photoemission spectroscopy and density functional theory shows that the narrowing of the band gap upon borane coordination to the pyridal nitrogen on PT is a result of lowering the energies of both the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of the optically relevant fragments; however, the LUMO is decreased to a greater extent, thereby giving rise to the narrowing of the gap.
Co-reporter:Lei Ying ; Ben B. Y. Hsu ; Hongmei Zhan ; Gregory C. Welch ; Peter Zalar ; Louis A. Perez ; Edward J. Kramer ; Thuc-Quyen Nguyen ; Alan J. Heeger ; Wai-Yeung Wong
Journal of the American Chemical Society 2011 Volume 133(Issue 46) pp:18538-18541
Publication Date(Web):September 21, 2011
DOI:10.1021/ja207543g
π-Conjugated, narrow band gap copolymers containing pyridal[2,1,3]thiadiazole (PT) were synthesized via starting materials that prevent random incorporation of the PT heterocycles relative to the backbone vector. Two regioregular structures could be obtained: in one the PTs are oriented in the same direction, and in the other the orientation of the PTs alternates every other repeat unit. Compared to their regiorandom counterparts, the regioregular polymers exhibit a 2 orders of magnitude increase of the hole mobilites, from 0.005 to 0.6 cm2 V–1 s–1, as determined by field-effect transistor measurements.
Co-reporter:Chengfen Xing;Libing Liu;Hongwei Tang;Xuli Feng;Qiong Yang;Shu Wang
Advanced Functional Materials 2011 Volume 21( Issue 21) pp:4058-4067
Publication Date(Web):
DOI:10.1002/adfm.201100840
Abstract
Multifunctional materials that simultaneously provide therapeutic action and image the results provide new strategies for the treatment of various diseases. Here, it is shown that water soluble conjugated polymers with a molecular design centered on the polythiophene−porphyrin dyad are effective for killing neighboring cells. Following photoexcitation, energy is efficiently transferred from the polythiophene backbone to the porphyrin units, which readily produce singlet oxygen (1O2) that is toxic for the cells. Due to the light-harvesting ability of the electronically delocalized backbone and the efficient energy transfer amongst optical partners, the polythiophene−porphyrin dyad shows a higher 1O2 generation efficiency than a small molecule analog. The fluorescent properties of these polymers can also serve to distinguish amongst living and dead cells. Polymers can be designed with folic acid grafted onto the polymer side chain that can specifically kill folate receptor-overexpressed cells, thereby providing an important demonstration of anticancer specificity through molecular design.
Co-reporter:Jung Hwa Seo;Ebinazar B. Namdas;Andrea Gutacker;Alan J. Heeger
Advanced Functional Materials 2011 Volume 21( Issue 19) pp:3667-3672
Publication Date(Web):
DOI:10.1002/adfm.201100682
Abstract
Improved performance of p-type organic light-emitting transistors (OLETs) is demonstrated by introducing a conjugated polyelectrolyte (CPE) layer and symmetric high work function (WF) source and drain metal electrodes. The OLET comprises a tri-layer film consisting of a hole transporting layer, an emissive layer, and a CPE layer as an electron injection layer. The thickness of the CPE layer is critical for achieving good performance and provides an important structural handle for consideration in future optimization studies. We also demonstrate for the first time, good performance solution-processed blue-emitting OLETs. These results further demonstrate the simplification of device fabrication and improved performance afforded by integrating CPE interlayers into organic optoelectronic devices.
Co-reporter:Jung Hwa Seo;Ebinazar B. Namdas;Andrea Gutacker;Alan J. Heeger
Advanced Functional Materials 2011 Volume 21( Issue 19) pp:
Publication Date(Web):
DOI:10.1002/adfm.201190084
Co-reporter:Aidee Duarte, Kan-Yi Pu, Bin Liu, and Guillermo C. Bazan
Chemistry of Materials 2011 Volume 23(Issue 3) pp:501
Publication Date(Web):November 9, 2010
DOI:10.1021/cm102196t
This review summarizes recent advances in the science and applications of conjugated polyelectrolytes (CPEs), with an emphasis on direct visual sensing, cellular imaging, and the fabrication of optoelectronic devices. CPEs backbones that incorporate donor−acceptor units are useful for direct visual sensing, whereas CPEs with hyperbranched structures, or biocompatible long side chains, are particularly useful for cellular imaging. With specially designed counterions, CPEs also demonstrate unique function in device fabrication and operation, for example, in dye-sensitized solar cells (DSSCs), bulk heterojunction (BHJ) solar cells, polymer light-emitting diodes (PLEDs), polymer light-emitting electrochemical cells (PLECs), and organic thin film transistors (OFET). Additionally, new strategies to modify and optimize CPE properties for specific applications are provided. The work summarized herein not only illustrates relationships between molecular structures and function, but also highlights how the structural versatility of CPEs makes them a unique category of multifunctional materials with the potential for fulfilling a variety of optical and electronic applications in solution, mixed media, and in the solid state.
Co-reporter:Gregory C. Welch, Louis A. Perez, Corey V. Hoven, Yuan Zhang, Xuan-Dung Dang, Alexander Sharenko, Michael F. Toney, Edward J. Kramer, Thuc-Quyen Nguyen and Guillermo C. Bazan
Journal of Materials Chemistry A 2011 vol. 21(Issue 34) pp:12700-12709
Publication Date(Web):22 Jul 2011
DOI:10.1039/C1JM11963J
We report on the design, synthesis and characterization of light harvesting small molecules for use in solution-processed small molecule bulk heterojunction (SM-BHJ) solar cell devices. These molecular materials are based upon an acceptor/donor/acceptor (A/D/A) core with donor endcapping units. Utilization of a dithieno(3,2-b;2′,3′-d)silole (DTS) donor and pyridal[2,1,3]thiadiazole (PT) acceptor leads to strong charge transfer characteristics, resulting in broad optical absorption spectra extending well beyond 700 nm. SM-BHJ solar cell devices fabricated with the specific example 5,5′-bis{7-(4-(5-hexylthiophen-2-yl)thiophen-2-yl)-[1,2,5]thiadiazolo[3,4-c]pyridine}-3,3′-di-2-ethylhexylsilylene-2,2′-bithiophene (6) as the donor and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) as the acceptor component showed short circuit currents above −10 mA cm−2 and power conversion efficiencies (PCEs) over 3%. Thermal processing is a critical factor in obtaining favorable active layer morphologies and high PCE values. A combination of UV-visible spectroscopy, conductive and photo-conductive atomic force microscopies, dynamic secondary mass ion spectrometry (DSIMS), and grazing incident wide angle X-ray scattering (GIWAXS) experiments were carried out to characterize how thermal treatment influences the active layer structure and organization.
Co-reporter:Nekane Guarrotxena and Guillermo C. Bazan
Chemical Communications 2011 vol. 47(Issue 31) pp:8784-8786
Publication Date(Web):07 Jul 2011
DOI:10.1039/C1CC12659H
Protein detection at the femtomolar level can be achieved by using metallic nanoparticle assemblies that function as surface enhanced Raman spectroscopy reporters and that contain suitable surface-bound recognition elements. Proper control of the interaction between nanoparticles within the assemblies is critical for achieving this performance.
Co-reporter:Logan E. Garner ; Juhyun Park ; Scott M. Dyar ; Arkadiusz Chworos ; James J. Sumner
Journal of the American Chemical Society 2010 Volume 132(Issue 29) pp:10042-10052
Publication Date(Web):July 7, 2010
DOI:10.1021/ja1016156
We report on the modification of membranes by incorporation of phenylenevinylene oligoelectrolytes with the goal of tailoring their optical and electronic properties and their applications. A water-soluble distyrylstilbene oligoelectrolyte (DSSN+), capped at each end with nitrogen bound, terminally charged pendant groups, was synthesized. The photophysical and solvatochromatic properties of DSSN+ and the shorter distyrylbenzene analogue DSBN+ were probed and found to be useful for characterizing insertion into membranes based on phospholipid vesicle systems. A combination of UV/visible absorbance and photoluminescence spectroscopies, together with confocal microscopy, were employed to confirm membrane incorporation. Examination of the emission intensity profile in stationary multilamellar vesicles obtained with a polarized excitation source provides insight into the orientation of these chromophores within lipid bilayers and indicates that these molecules are highly ordered, such that the hydrophobic electronically delocalized region positions within the inner membrane with the long molecular axis perpendicular to the bilayer plane. Cyclic voltammetry experiments provide evidence that DSSN+ and DSBN+ facilitate transmembrane electron transport across lipid bilayers supported on glassy carbon electrodes. Additionally, the interaction with living microorganisms was probed. Fluorescence imaging indicates that DSSN+ and DSBN+ preferentially accumulate within cell membranes. Furthermore, notable increases in yeast microbial fuel cell performance were observed when employing DSSN+ as the electron transport mediator.
Co-reporter:Zhao Chen ; Xuan-Dung Dang ; Andrea Gutacker ; Andrew Garcia ; Huaping Li ; Yunhua Xu ; Lei Ying ; Thuc-Quyen Nguyen
Journal of the American Chemical Society 2010 Volume 132(Issue 35) pp:12160-12162
Publication Date(Web):August 16, 2010
DOI:10.1021/ja1056856
Surface reconstruction of electron injection layers based on conjugated oligoelectrolytes atop an electroluminescent layer occurs in the presence of air. The proposed mechanism involves hydration and concomitant increase of the interfacial energy with the underlying hydrophobic surface followed by dewetting via a nucleation process. No such changes are observed in the case of a conjugated polyelectrolyte, presumably because the lower mobility of the polymer chains leads to a kinetically locked bilayer.
Co-reporter:Aidee Duarte ; Arkadiusz Chworos ; Suvi F. Flagan ; Grady Hanrahan
Journal of the American Chemical Society 2010 Volume 132(Issue 36) pp:12562-12564
Publication Date(Web):August 23, 2010
DOI:10.1021/ja105747b
Electrostatic complexes containing a cationic conjugated oligoelectrolyte (COE) and fluorescein (FAM)-labeled single-stranded DNA (ssDNA) serve as the basis for identifying various bacteria. The approach involves the preparation of five COE/ssDNAx-FAM electrostatic complexes, which differ in the ssDNA composition and which provide different photoluminescence (PL) spectra as a result of different degrees of energy transfer efficiency from the COE to FAM. Changes in the PL spectra upon addition of the bacteria can be quantified, and the differential response from the five ssDNAs gives rise to a multicomponent array response that allows identification of the microorganism under investigation.
Co-reporter:Robert C. Coffin ; Yanika Schneider ; Edward J. Kramer
Journal of the American Chemical Society 2010 Volume 132(Issue 39) pp:13869-13878
Publication Date(Web):September 13, 2010
DOI:10.1021/ja1056938
Novel binuclear complexes, 4,4′-bis{[N-(2,6-diisopropylphenyl)-2-(2,6-diisopropylphenylimino)propanamidato-κ2-N,O-(trimethylphosphine)nickel(II)]methyl}-1,1′-biphenyl (2a) and 4,4′-bis{[N-(2,6-diisopropylphenyl)-2-(2,6-diisopropylphenylimino)-4-methylpentamidato-κ2-N,O-(trimethylphosphine)nickel(II)]methyl}-1,1′-biphenyl (2b), were synthesized by linking two nickel centers through a bis(benzyl) fragment. When activated with nickel bis(1,5-cyclooctadiene) (Ni(COD)2), 2a and 2b are capable of polymerizing ethylene in a quasi-living fashion, producing polymers with approximately twice the molecular weights relative to those obtained by using a structurally related mononuclear system. In addition, 2b/Ni(COD)2 was utilized to synthesize a series of pseudo-triblock polyethylene (PE) macroinitiating copolymers, bearing atom-transfer radical polymerization (ATRP) initiators. Pseudo-pentablock copolymers were also prepared by taking advantage of a pressure-pulsing technique, wherein the ethylene pressure was increased from 100 to 500 psi in order to produce semicrystalline ethylene-rich end-blocks. Copolymers with elastomeric properties were synthesized by grafting n-butyl acrylate from the PE macroinitiators via ATRP. Examination using monotonic and step-cyclic stress−strain tests demonstrates that the materials exhibit large strains at break (1600−2000%) and excellent elastic recoveries at large strains (∼80%). That materials with such desirable properties could not be attained using a mononuclear initiator demonstrates the clear advantage of growing the polymer via a telechelic mechanism.
Co-reporter:Frank A. Leibfarth ; Yanika Schneider ; Nathaniel A. Lynd ; Alison Schultz ; Bongjin Moon ; Edward J. Kramer ; Guillermo C. Bazan ;Craig J. Hawker
Journal of the American Chemical Society 2010 Volume 132(Issue 42) pp:14706-14709
Publication Date(Web):October 5, 2010
DOI:10.1021/ja1060643
The functionalization and cross-linking of polyethylene is synthetically challenging, commonly relying on highly optimized radical based postpolymerization strategies. To address these difficulties, a norbornene monomer containing Meldrum’s acid is shown to be effectively copolymerized with polyethylene using a nickel α-iminocarbaxamidato complex, providing high-melting, semicrystalline polymers with a tunable incorporation of the functional comonomer. Upon heating the copolymer to common polyethylene processing temperatures, the thermolysis of Meldrum’s acid to ketene provides the desired reactive group. This simple and versatile methodology does not require small molecule radical sources or catalysts, and the dimerization of the in situ generated ketenes is shown to provide tunable cross-linking densities in polyethylene. Subsequent rheological and tensile experiments illustrate the ability to tune cross-linked polyethylene properties by comonomer incorporation and elucidate valuable structure/property relationships in these materials. This study illustrates the power of well-defined and synthetically accessible functional groups in polyolefin synthesis and functionalization.
Co-reporter:Minghong Tong;Shinuk Cho;James T. Rogers;Kristin Schmidt;Ben B. Y. Hsu;Daniel Moses;Robert C. Coffin;Edward J. Kramer;Alan J. Heeger
Advanced Functional Materials 2010 Volume 20( Issue 22) pp:3959-3965
Publication Date(Web):
DOI:10.1002/adfm.201001271
Abstract
Increasing the molecular weight of the low-bandgap semiconducting copolymer, poly[(4,4-didoecyldithieno[3,2-b:2′,3′-d]silole)-2,6-diyl-alt-(2,1,3-benzothiadiazole)-4,7-diyl], Si-PDTBT, from 9 kDa to 38 kDa improves both photoresponsivity and charge transport properties dramatically. The photocurrent measured under steady state conditions is 20 times larger in the higher molecular weight polymer (HMn Si-PDTBT). Different decays of polarization memory in transient photoinduced spectroscopy measurements are consistent with more mobile photoexcitations in HMn Si-PDTBT relative to the lower molecular weight counterpart (LMn Si-PDTBT). Analysis of the current-voltage characteristics of field effect transistors reveals an increase in the mobility by a factor of 700 for HMn Si-PDTBT. Near edge X-ray absorption fine structure (NEXAFS) spectroscopy and grazing incidence small angle X-ray scattering (GISAXS) measurements demonstrate that LMn Si-PDTBT forms a disordered morphology throughout the depth of the film, whereas HMn Si-PDTBT exhibits pronounced π-π stacking in an edge-on configuration near the substrate interface. Increased interchain overlap between polymers in the edge-on configuration in HMn Si-PDTBT results in the higher carrier mobility. The improved optical response, transport mobility, and interfacial ordering highlight the subtle role that the degree of polymerization plays on the optoelectronic properties of conjugated polymer based organic semiconductors.
Co-reporter:Chao He, Chengmei Zhong, Hongbin Wu, Renqiang Yang, Wei Yang, Fei Huang, Guillermo C. Bazan and Yong Cao
Journal of Materials Chemistry A 2010 vol. 20(Issue 13) pp:2617-2622
Publication Date(Web):09 Feb 2010
DOI:10.1039/B921775D
It has been previously shown that incorporating alcohol/water-soluble conjugated polyelectrolytes (CPEs) as cathode interlayers can substantially enhance the open-circuit voltage (Voc) of bulk heterojunction polymer solar cells (PSCs). This improvement is attractive since there are only a few solution-based processing technologies that can enhance the Voc. In this article, the Voc enhancement effect of five distinct CPE materials was studied on three typical PSC device configurations, each using different donor materials. Significant Voc enhancement was observed in devices that contain a polyfluorene copolymer as the donor material. The origin of the Voc enhancement was investigated by examination of the dark currents.
Co-reporter:Jason D. Azoulay;Zachary A. Koretz;Guang Wu ;Dr. Guillermo C. Bazan
Angewandte Chemie 2010 Volume 122( Issue 43) pp:8062-8066
Publication Date(Web):
DOI:10.1002/ange.201003125
Co-reporter:Jason D. Azoulay;Zachary A. Koretz;Guang Wu ;Dr. Guillermo C. Bazan
Angewandte Chemie International Edition 2010 Volume 49( Issue 43) pp:7890-7894
Publication Date(Web):
DOI:10.1002/anie.201003125
Co-reporter:Dr. Yan Ren; Guillermo C. Bazan
Chemistry - A European Journal 2010 Volume 16( Issue 36) pp:11028-11036
Publication Date(Web):
DOI:10.1002/chem.201000885
Abstract
Conjugated oligoelectrolytes (COEs) are being introduced into a variety of optical and electronic technologies, yet the dependence of their properties as a function of molecular structure remains poorly understood. In response, we designed, synthesized, and examined a new tetracationic COE, namely, 1,4-bis{9′,9′-bis[6′′-(N,N,N-trimethylammonium)hexyl]-2′-fluorenyl}-2,5-bis(trifluoromethyl)benzene tetrabromide (FPF-F6), which contains bulky electron-withdrawing trifluoromethyl groups, and compared its properties with the unsubstituted counterpart 1,4-bis{9′,9′-bis[6′′-(N,N,N-trimethylammonium)hexyl]-2′-fluorenyl}benzene tetrabromide (FPF). The ground-state geometry of FPF-F6 is primarily twisted with little electronic communication between the aromatic units, as confirmed by single-crystal X-ray diffraction studies of the neutral precursor. However, absorption and photoluminescence spectroscopies reveal that the excited state of FPF-F6 displays strong intramolecular charge-transfer characteristics. Solution AFM in aqueous media shows that introduction of trifluoromethyl groups changes the size and aspect ratio of supramolecular aggregates that are brought together as a result of hydrophobic interactions. Furthermore, addition of ssDNA to FPF-F6 leads to interoligoelectrolyte complexes wherein the backbone is more planar; the environment the chromophore experiences under these conditions is also considerably less polar. These findings provide considerable insight into the complex photophysics of electronically conjugated materials in aqueous media.
Co-reporter:Jeffrey Peet, Alan J. Heeger and Guillermo C. Bazan
Accounts of Chemical Research 2009 Volume 42(Issue 11) pp:1700
Publication Date(Web):July 1, 2009
DOI:10.1021/ar900065j
As the global demand for low-cost renewable energy sources intensifies, interest in new routes for converting solar energy to electricity is rapidly increasing. Although photovoltaic cells have been commercially available for more than 50 years, only 0.1% of the total electricity generated in the United States comes directly from sunlight. The earliest commercial solar technology remains the basis for the most prevalent devices in current use, namely, highly-ordered crystalline, inorganic solar cells, commonly referred to as silicon cells. Another class of solar cells that has recently inspired significant academic and industrial excitement is the bulk heterojunction (BHJ) “plastic” solar cell. Research by a rapidly growing community of scientists across the globe is generating a steady stream of new insights into the fundamental physics, the materials design and synthesis, the film processing and morphology, and the device science and architecture of BHJ technology. Future progress in the fabrication of high-performance BHJ cells will depend on our ability to combine aspects of synthetic and physical chemistry, condensed matter physics, and materials science. In this Account, we use a combination of characterization tools to tie together recent advances in BHJ morphology characterization, device photophysics, and thin-film solution processing, illustrating how to identify the limiting factors in solar cell performance. We also highlight how new processing methods, which control both the BHJ phase separation and the internal order of the components, can be implemented to increase the power conversion efficiency (PCE). The failure of many innovative materials to achieve high performance in BHJ solar cell devices has been blamed on “poor morphology” without significant characterization of either the structure of the phase-separated morphology or the nature of the charge carrier recombination. We demonstrate how properly controlling the “nanomorphology”, which is critically dependent on minute experimental details at every step, from synthesis to device construction, provides a clear path to >10% PCE BHJ cells, which can be fabricated at a fraction of the cost of conventional solar cells.
Co-reporter:Brycelyn M. Boardman and Guillermo C. Bazan
Accounts of Chemical Research 2009 Volume 42(Issue 10) pp:1597
Publication Date(Web):August 6, 2009
DOI:10.1021/ar900097b
Polyolefins constitute a vast class of macromolecules that range from everyday plastics to sophisticated materials used as hip-replacement joints and in bulletproof vests. By tailoring the molecular structure of the backbone, researchers can tune the bulk properties of these materials for specific product applications. Transition-metal complexes that mediate the polymerization of ethylene, 1-alkenes, and related monomers provide an important tool for industrial preparation. Although commercially viable options exist for large-scale manufacturing, it is not possible to achieve all desirable polymer targets using these methods. For example, the copolymerization of ethylene with co-monomers bearing polar functionalities under living conditions, where there is high activity and minimum chain transfer and termination, is not available at this scale. Also, given the magnitude of polyolefin production, we anticipate a need to more efficiently manage chemical resources. For these reasons, new metal/catalyst combinations and methods for their applications continue to be an active area of research in both academic and industrial laboratories. This Account focuses on the chemistry of α-iminocarboxamidato complexes of nickel carried out in our laboratories. Such complexes can serve as precursors to zwitterionic or neutral active species, depending upon the mode of activation. We have successfully applied the zwitterionic systems in the tandem action of multiple active sites to yield branched polyethylene from ethylene alone; a coordinated effort of catalysts that is reminiscent of metabolic pathways. These polymerizations show many of the characteristics of living polymerizations. The neutral initiators allow for the controlled preparation of copolymers containing ethylene and functionalized co-monomers and can be used to access higher order polymer architectures, such as block, tapered, and pseudo-tetrablock copolymers. Many of these polymers are not readily available using other catalytic methods. In this Account, we first provide a historical narrative of developments leading to ligands derived from the α-iminocarboxamide framework. Second, we explore how structural variations of this ligand system are readily obtained and how they can be used to provide insight into the mechanism of activation and for controlling polymerization reactions. We conclude by describing emerging applications, particularly in the area of graft copolymers.
Co-reporter:Jung Hwa Seo;Renqiang Yang;Jacek Z. Brzezinski;Bright Walker;Thuc-Quyen Nguyen
Advanced Materials 2009 Volume 21( Issue 9) pp:1006-1011
Publication Date(Web):
DOI:10.1002/adma.200802420
Co-reporter:Yunhua Xu;Renqiang Yang;Junbiao Peng;Alexer A. Mikhailovsky;Yong Cao;Thuc-Quyen Nguyen
Advanced Materials 2009 Volume 21( Issue 5) pp:584-588
Publication Date(Web):
DOI:10.1002/adma.200802548
Co-reporter:Huaping Li
Advanced Materials 2009 Volume 21( Issue 9) pp:964-967
Publication Date(Web):
DOI:10.1002/adma.200802320
Co-reporter:Huaping Li
Advanced Materials 2009 Volume 21( Issue 9) pp:
Publication Date(Web):
DOI:10.1002/adma.200990030
Co-reporter:Gregory C. Welch ; Robert Coffin ; Jeff Peet
Journal of the American Chemical Society 2009 Volume 131(Issue 31) pp:10802-10803
Publication Date(Web):July 8, 2009
DOI:10.1021/ja902789w
A simple and effective strategy for optical band gap control is demonstrated through the use of a novel small acceptor/donor/acceptor molecule, 1, and group-13 Lewis acids. Chromophore 1 contains a dithienolesilole donor unit end-capped with benzo-2,1,3-thiadiazole (BT) acceptor units. Addition to 1 of stoichiometeric quantities of Lewis acids of varying strength resulted in the formation of Lewis adducts with progressively red-shifted primary charge-transfer absorption bands. These complexes have absorption spectra that approach those of known conjugated copolymers containing related units. NMR spectroscopy and X-ray diffraction studies revealed that 1 binds 2 equiv of Lewis acid via the nitrogen at the 3-position of BT.
Co-reporter:Cheng Wang ; Andres Garcia ; Hongping Yan ; Karen E. Sohn ; Alexander Hexemer ; Thuc-Quyen Nguyen ; Guillermo C. Bazan ; Edward J. Kramer ;Harald Ade
Journal of the American Chemical Society 2009 Volume 131(Issue 35) pp:12538-12539
Publication Date(Web):August 13, 2009
DOI:10.1021/ja905293m
The interfaces of conjugated polyelectrolyte (CPE)/poly[2-methoxy-5-(2′-ethylhexyloxy)-p-phenylene vinylene] (MEH-PPV) bilayers cast from differential solvents are shown by resonant soft X-ray reflectivity (RSoXR) to be very smooth and sharp. The chemical interdiffusion due to casting is limited to less than 0.6 nm, and the interface created is thus nearly “molecularly” sharp. These results demonstrate for the first time and with high precision that the nonpolar MEH-PPV layer is not much disturbed by casting the CPE layer from a polar solvent. A baseline is established for understanding the role of interfacial structure in determining the performance of CPE-based polymer light-emitting diodes. More broadly, we anticipate further applications of RSoXR as an important tool in achieving a deeper understanding of other multilayer organic optoelectronic devices, including multilayer photovoltaic devices.
Co-reporter:Jason D. Azoulay, Yanika Schneider, Griselda B. Galland and Guillermo C. Bazan
Chemical Communications 2009 (Issue 41) pp:6177-6179
Publication Date(Web):10 Sep 2009
DOI:10.1039/B912743G
A nickel α-keto-β-diimine initiator can be activated using treated methylaluminoxane (MAO) to generate active sites capable of the polymerization of ethylene, propene and 1-hexene under living conditions.
Co-reporter:JasonD. Azoulay;ReneS. Rojas Dr.;AbigailV. Serrano;Hisashi Ohtaki;GriseldaB. Gall Dr.;Guang Wu Dr.;GuillermoC. Bazan Dr.
Angewandte Chemie 2009 Volume 121( Issue 6) pp:
Publication Date(Web):
DOI:10.1002/ange.200990013
Co-reporter:JasonD. Azoulay;ReneS. Rojas Dr.;AbigailV. Serrano;Hisashi Ohtaki;GriseldaB. Gall Dr.;Guang Wu Dr.;GuillermoC. Bazan Dr.
Angewandte Chemie International Edition 2009 Volume 48( Issue 6) pp:
Publication Date(Web):
DOI:10.1002/anie.200990016
Co-reporter:Yanika Schneider, Nathaniel A. Lynd, Edward J. Kramer and Guillermo C. Bazan
Macromolecules 2009 Volume 42(Issue 22) pp:8763-8768
Publication Date(Web):October 7, 2009
DOI:10.1021/ma901796f
A series of polyethylene-based macroinitiators bearing atom transfer radical polymerization (ATRP) initiator functionalities were prepared by copolymerizing norbornen-2-yl-2-bromo-2-methylpropanoate (3) with ethylene using N-(2,6-diisopropylphenyl)-2-(2,6-diisopropylphenyl-imino)isobutanamidato]-Ni(η1CH2Ph) (PMe3) (1) and bis(1,5-cyclooctadiene)nickel (2). The content of 3 was increased from 2 to 16 mol %, and the mechanical properties of the resulting macroinitiators were investigated using monotonic and step cyclic stress−strain tests. With increasing 3 content, the product transitioned from plastically deforming PE to elastomeric PE (at 10 mol % 3) to a brittle polynorbornene-like material. Upon grafting with n-butyl acrylate (nBA) using ATRP, the new materials became significantly softer and more elastomeric in comparison to their parent macroinitiators. Increasing nBA content did not break up the PE crystallites, but instead diluted the overall crystallinity and decreased the glass transition temperature of the products. The highest performing acrylate-containing polyolefin elastomer exhibited an elongation at break of 780% strain and a recovery of 83% at 400% strain.
Co-reporter:Lingling An;Libing Liu Dr.;Shu Wang ;GuillermoC. Bazan
Angewandte Chemie International Edition 2009 Volume 48( Issue 24) pp:4372-4375
Publication Date(Web):
DOI:10.1002/anie.200900758
Co-reporter:JasonD. Azoulay;ReneS. Rojas Dr.;AbigailV. Serrano;Hisashi Ohtaki;GriseldaB. Gall Dr.;Guang Wu Dr.;GuillermoC. Bazan Dr.
Angewandte Chemie International Edition 2009 Volume 48( Issue 6) pp:1089-1092
Publication Date(Web):
DOI:10.1002/anie.200804661
Co-reporter:JasonD. Azoulay;ReneS. Rojas Dr.;AbigailV. Serrano;Hisashi Ohtaki;GriseldaB. Gall Dr.;Guang Wu Dr.;GuillermoC. Bazan Dr.
Angewandte Chemie 2009 Volume 121( Issue 6) pp:1109-1112
Publication Date(Web):
DOI:10.1002/ange.200804661
Co-reporter:Brycelyn M. Boardman, Guang Wu, Rene Rojas, Guillermo C. Bazan
Journal of Organometallic Chemistry 2009 694(9–10) pp: 1380-1384
Publication Date(Web):
DOI:10.1016/j.jorganchem.2008.12.038
Co-reporter:J. H. Ortony;R. Q. Yang;J. Z. Brzezinski;L. Edman;T.-Q. Nguyen;G. C. Bazan
Advanced Materials 2008 Volume 20( Issue 2) pp:298-302
Publication Date(Web):
DOI:10.1002/adma.200701627
Co-reporter:Jeffrey Peet;Erin Brocker;Yunhua Xu
Advanced Materials 2008 Volume 20( Issue 10) pp:1882-1885
Publication Date(Web):
DOI:10.1002/adma.200702515
Co-reporter:Juhyun Park;Renqiang Yang;Corey V. Hoven;Andres Garcia;Daniel A. Fischer;Thuc-Quyen Nguyen;Dean M. DeLongchamp
Advanced Materials 2008 Volume 20( Issue 13) pp:2491-2496
Publication Date(Web):
DOI:10.1002/adma.200702995
Co-reporter:Corey V. Hoven;Andres Garcia;Thuc-Quyen Nguyen
Advanced Materials 2008 Volume 20( Issue 20) pp:3793-3810
Publication Date(Web):
DOI:10.1002/adma.200800533
Abstract
Conjugated polyelectrolytes comprise an electronically delocalized backbone with pendant groups bearing ionic functionalities. Important new developments regarding their use to improve charge injection from metallic electrodes into organic semiconductors, a key requirement in emissive devices, have recently appeared. This article provides an overview of recent studies concerning the basic properties of conjugated polyelectrolytes as a function of molecular structure, and of optoelectronic devices with conjugated polyelectrolytes as essential functional components. Processes where more insightful mechanistic understanding is needed and areas of opportunity are discussed.
Co-reporter:H. B. Wu;J. H. Zou;F. Liu;L. Wang;A. Mikhailovsky;G. C. Bazan;W. Yang;Y. Cao
Advanced Materials 2008 Volume 20( Issue 4) pp:696-702
Publication Date(Web):
DOI:10.1002/adma.200701329
Co-reporter:Laura Fabris;Mark Dante;Thuc-Quyen Nguyen;Jeffrey B.-H. Tok
Advanced Functional Materials 2008 Volume 18( Issue 17) pp:
Publication Date(Web):
DOI:10.1002/adfm.200890066
Co-reporter:Chunyan Chi;Arkadiusz Chworos;Jinping Zhang;Alexer Mikhailovsky
Advanced Functional Materials 2008 Volume 18( Issue 22) pp:3606-3612
Publication Date(Web):
DOI:10.1002/adfm.200800675
Abstract
Conjugated polyelectrolytes (CPEs) have been widely used as light harvesting macromolecules to amplify the signals of fluorescent assays that betray the presence of various biomolecular targets. Electrostatic interactions play an important role in coordinating optical coupling events and lead to the formation of complexes between oppositely charged CPEs and the target species. Here, we combine for the first time optical studies and structural characterization by liquid phase atomic force microscopy (AFM) to provide a picture of aggregate structure and growth dynamics between cationic CPE and DNA as a function of charge ratio. Specifically, poly120, a copolymer containing a backbone with 50% fluorene, 30% phenylene, and 20% 2,1,3-benzothiadiazole (BT) units and pendant cationic groups was mixed with single stranded DNA (ssDNA) labeled with the Cy5 acceptor chromophore. Continuous addition of ssDNA-Cy5 to poly120 leads to a saturation in Cy5 emission due to Cy5–Cy5 self-quenching. Addition of ssDNA to a preformed poly120/ssDNA-Cy5 solution results in increased sensitization by energy transfer and a reduction of Cy5–Cy5 self quenching. Adsorption of aggregates onto negatively charged mica under water allows for direct imaging of the polyelectrolyte complexes as a function of charge ratio. The composite set of observations allows for the development of a model for aggregate growth, which is dynamic and ceases when the surface charge becomes sufficiently negative. This saturation point can be mitigated by addition of unlabeled ssDNA.
Co-reporter:Chunyan Chi;Arkadiusz Chworos;Jinping Zhang;Alexer Mikhailovsky
Advanced Functional Materials 2008 Volume 18( Issue 22) pp:
Publication Date(Web):
DOI:10.1002/adfm.200890091
Co-reporter:Laura Fabris;Mark Dante;Thuc-Quyen Nguyen;Jeffrey B.-H. Tok
Advanced Functional Materials 2008 Volume 18( Issue 17) pp:2518-2525
Publication Date(Web):
DOI:10.1002/adfm.200800301
Abstract
We report here “aptatags,” which consist of aptamer-modified silver nanoparticles (NPs) held together by an optical reporter. It is possible to use these materials to design a heterogeneous method for protein identification that takes advantage of the Raman signal enhancement by metallic nanostructures and the recognition capabilities of aptamers. Aptatags are formed by linking silver NPs with an organic dithiol molecule, followed by surface modification with thiolated single-stranded DNA (ssDNA) corresponding to the sequence of the aptamer probe. The sensing surface involves a silver layer containing the thiolated capturing aptamer and mercaptohexadecanoic acid to minimize nonspecific binding. The overall process provides excellent selectivity and sensitivity. Detailed characterization of the sensing surface by SERS maps and atomic force microscopy was carried out to understand how structural features lead to signal generation.
Co-reporter:Nam Sung Cho, Shinuk Cho, Mark Elbing, Jae Kwan Lee, Renqiang Yang, Jung Hwa Seo, Kwanghee Lee, Guillermo C. Bazan and Alan J. Heeger
Chemistry of Materials 2008 Volume 20(Issue 20) pp:6289
Publication Date(Web):October 1, 2008
DOI:10.1021/cm801601r
Co-reporter:Nam Sung Cho, Sang Kyu Lee, Jung Hwa Seo, Mark Elbing, Jason D. Azoulay, Juhyun Park, Shinuk Cho, Alan J. Heeger and Guillermo C. Bazan
Journal of Materials Chemistry A 2008 vol. 18(Issue 41) pp:4909-4911
Publication Date(Web):29 Sep 2008
DOI:10.1039/B813051E
α,ω-Dihexylthienoselenophenes (Se2Thx) are readily prepared oligomeric species that can be used as the semiconducting layer in organic thin film transistors (TFTs). These selenophene-containing oligomers exhibit high hole mobilities (0.023 and 0.16 cm2 V−1 s−1) and good on/off ratio (105–106) that are improved relative to their sulfur-containing counterparts. X-Ray diffraction measurements and atomic force microscopy give insight into the internal structure and surface topography of the materials.
Co-reporter:Mark Elbing Dr. ;GuillermoC. Bazan Dr.
Angewandte Chemie 2008 Volume 120( Issue 5) pp:846-850
Publication Date(Web):
DOI:10.1002/ange.200703722
Co-reporter:Mark Elbing Dr. ;GuillermoC. Bazan Dr.
Angewandte Chemie International Edition 2008 Volume 47( Issue 5) pp:834-838
Publication Date(Web):
DOI:10.1002/anie.200703722
Co-reporter:Brycelyn M. Boardman, Juan M. Valderrama, Flor Muñoz, Guang Wu, Guillermo C. Bazan and Rene Rojas
Organometallics 2008 Volume 27(Issue 8) pp:1671-1674
Publication Date(Web):March 25, 2008
DOI:10.1021/om700933y
The synthesis of two new organometallic species, compounds 1 and 2, allows for the investigation of remote activation through an exocyclic CN functionality. The in situ generation of 2 from 1 plus excess B(C6F5)3 yields polyethylene possessing a bimodal distribution.
Co-reporter:Jason D. Azoulay, Koji Itigaki, Guang Wu and Guillermo C. Bazan
Organometallics 2008 Volume 27(Issue 10) pp:2273-2280
Publication Date(Web):April 16, 2008
DOI:10.1021/om8000263
A series of N,O-bound, neutral nickel complexes containing α-iminocarboxamide, η1-CH2Ph, and PMe3 ligands were synthesized to examine the effect of steric and electronic variations at the site adjacent to the imine functionality. These complexes were subsequently activated with Ni(COD)2 for use in ethylene homopolymerization and ethylene/norbornene acetate (NBA) copolymerization reactions. As the bulk of the substituents is increased, one observes a progressive decrease in the rate of ring rotation, a more crowded coordination sphere around nickel, increased monomer consumption activity, and higher molecular weights of the products. Copolymerization reactions showed that the increased crowding around nickel decreases the reactivity of NBA relative to ethylene. As electron density is removed from the metal center, the catalytic species become more active toward ethylene and are more prone to interact with the functionality on NBA.
Co-reporter:Jeffrey Peet, Nam Sung Cho, Sang Kyu Lee and Guillermo C. Bazan
Macromolecules 2008 Volume 41(Issue 22) pp:8655-8659
Publication Date(Web):October 27, 2008
DOI:10.1021/ma801945h
Certain solvent additives significantly affect the morphology of the active layer in bulk heterojunction (BHJ) conjugated polymer solar cells and improve the device performance. Previous examinations of the BHJ films have shown that the best additives are characterized by higher boiling points than the host solvent and are poorer solvents for the conjugated host polymer than for the fullerene acceptor; however, little in the way of a mechanistic explanation has been presented, particularly on the dynamics of the transition from solution to the bulk material. This article combines spectroscopic analysis in various solvent mixtures and during solvent evaporation to show that a key feature of the film growth concerns aggregation of polymer chains into more ordered supramolecular structures prior to complete drying. The driving force for aggregation occurs in a medium that (a) is more fluid and allows chains to find optimal registry or conformations and (b) can solvate the fullerenes. We propose that when a single solvent that is good for the two components of the BHJ blend is used, the chains remain solvated up to a point where viscosity inhibits their motion and they are unable to attain similar packing characteristics.
Co-reporter:Mark Elbing, Andres Garcia, Slawomir Urban, Thuc-Quyen Nguyen and Guillermo C. Bazan
Macromolecules 2008 Volume 41(Issue 23) pp:9146-9155
Publication Date(Web):November 11, 2008
DOI:10.1021/ma802139j
The synthesis and characterization of a conjugated polymer with a thienothiophene-bithiophene-backbone and its corresponding polyelectrolyte structure is described. The conjugated polyelectrolyte is obtained by common nucleophilic substitution in solution, as well as by exposure of films of the neutral precursor to trimethylamine gas. X-ray photoelectron spectroscopy (XPS) analysis is used to determine the extent of conversion, at least within the top 10 nm of the film. Attempts to determine hole mobilities by using steady-state current−voltage (I−V) measurements using hole-only diodes containing the conjugated polyelectrolyte films give rise to light-emitting electrochemical behavior, indicating ion motion and/or redistribution within the films. The use of a pulsed I−V method operating at frequencies higher than the ion response times allows measurements of hole mobilities and suppresses ion motion. The reported mobilities are about 3 orders of magnitude higher than those reported for other thiophene-based polyelectrolytes. Overall, these results provide a new method for incorporating conjugated polyelectrolytes into device structures under circumstances where the material is not sufficiently soluble for deposition with standard techniques such as spin-coating.
Co-reporter:Corey V. Hoven;Renqiang Yang;Andres Garcia;Victoria Crockett;Alan J. Heeger;Thuc-Quyen Nguyen;
Proceedings of the National Academy of Sciences 2008 105(35) pp:12730-12735
Publication Date(Web):August 25, 2008
DOI:10.1073/pnas.0806494105
We show that polymer light-emitting diodes with high work-function cathodes and conjugated polyelectrolyte injection/transport
layers exhibit excellent efficiencies despite large electron-injection barriers. Correlation of device response times with
structure provides evidence that the electron-injection mechanism involves redistribution of the ions within the polyelectrolyte
electron-transport layer and hole accumulation at the interface between the emissive and electron-transport layers. Both processes
lead to screening of the internal electric field and a lowering of the electron-injection barrier. The hole and electron currents
are therefore diffusion currents rather than drift currents. The response time and the device performance are influenced by
the type of counterion used.
Co-reporter:H. Y. Woo;D. Vak;D. Korystov;A. Mikhailovsky;G. C. Bazan;D.-Y. Kim
Advanced Functional Materials 2007 Volume 17(Issue 2) pp:
Publication Date(Web):12 DEC 2006
DOI:10.1002/adfm.200600093
Two water-soluble conjugated polyelectrolytes, poly(9,9′-bis(6-N,N,N-trimethylammoniumhexyl)fluorene-alt-1,4-(2,5-bis(6-N,N,N-trimethylammoniumhexyloxy))phenylene) tetrabromide (P1i) and poly((10,10′-bis(6-N,N,N-trimethylammoniumhexyl)-10H-spiro(anthracene-9,9′-fluorene))-alt-1,4-(2,5-bis(6-N,N,N-trimethylammoniumhexyloxy))phenylene) tetrabromide (P2i) are synthesized, characterized, and used in fluorescence resonance energy transfer (FRET) experiments with fluorescein-labeled single-stranded DNA (ssDNA-Fl). P1i and P2i have nearly identical π-conjugated backbones, as determined by cyclic voltammetry and UV-vis spectroscopy. The main structural difference is the presence of an anthracenyl substituent, orthogonal to the main chain in each of the P2i repeat units, which increases the average interchain separation in aggregated phases. It is possible to observe emission from ssDNA-Fl via FRET upon excitation of P2i. Fluorescein is not emissive within the ssDNA-Fl/P1i electrostatic complex, suggesting Fl emission quenching through photoinduced charge transfer (PCT). We propose that the presence of the anthracenyl “molecular bumper” in P2i increases the distance between optical partners, which decreases PCT more acutely relative to FRET.
Co-reporter:B. Liu;T. T. T. Dan;G. C. Bazan
Advanced Functional Materials 2007 Volume 17(Issue 14) pp:
Publication Date(Web):15 AUG 2007
DOI:10.1002/adfm.200600821
A cationic water-soluble tetrahedral molecule bearing four phenylene-bis(fluorene) optical units, namely tetrakis[4-(2-(9,9,9′,9′-tetrakis(N,N,N-trimethylammoniumhexyl)-7,2′-bifluorenyl))-phenyl]methane hexadecanebromide, was designed and synthesized. Fluorescence resonance energy transfer (FRET) experiments between the tetrahedral molecule and fluorescein-labeled double stranded DNA (dsDNA-Fl) or single stranded DNA (ssDNA-Fl) were undertaken. Due to its specific shape and spatial registry, the tetrahedral molecule shows improved FRET efficiencies to dsDNA-Fl as well as improved selectivity between dsDNA and ssDNA, when compared to a cationic conjugated polymer with similar repeat units. 30-Fold signal amplification for dsDNA/ethidium bromide (EB) and selective response between complementary and non-complementary DNA indicates that tetrahedral molecules could be useful to amplify the optical response from EB-based DNA protocols.
Co-reporter:
Nature Protocols 2007 2(9) pp:
Publication Date(Web):2007-08-30
DOI:10.1038/nprot.2007.307
DNA microarrays are valuable tools in gene mapping, transcription profiling and genome comparison by allowing high-throughput screening of thousands of genes on a single slide1, 2, 3, 4. Traditional gene chips and DNA microarrays work by hybridizing fluorescently labeled target(s) to a large set of DNA sequences immobilized on a solid surface (usually glass). Monitoring the fluorescence intensity at a known probe location indicates the presence and relative quantity of the target(s) of interest. In traditional microarray work, targets must be labeled with a fluorescent marker before hybridization, which adds to the cost, complexity and time required to process the arrays. Working toward a label-free system will help to reduce the cost and time associated with target labeling procedures. Other label-free detection methods exist but typically require sophisticated instruments such as mass spectrometers. These instruments require substantial maintenance and are less suitable for high-throughput detection5. Recent studies have shown that cationic conjugated polymers (CCPs) can be incorporated into PNA-based label-free microarray assays6, 7. The overall detection strategy is schematically illustrated in Figure 1. Hybridization of single-stranded DNA (ssDNA) (negative, shown in blue) to the immobilized PNA (neutral, shown in black) on the substrate results in a negatively charged surface at that probe/target spot. Electrostatic interaction brings the CCP (shown in orange) to the hybridized DNA and enables preferential adsorption of CCP onto sites containing complementary ssDNA. Presence of target(s) can now be detected by the emission from the polymer alone, without the need for covalent labeling of the target before hybridization.PFBT is a cationic, water-soluble conjugated polymer. This polymer is capable of absorbing light at 488 nm and has efficient emission in the solid state, making it compatible with a variety of commercial microarray scanners. The synthesis and characterization of PFBT was initially published and later detailed in Nature Protocols by Liu and Bazan6, 8. The application of PFBT to a label-free microarray system requires simple binding and washing procedures following target hybridization. Other cationic conjugated polyelectrolytes should work in a similar fashion, provided that they have similar solubility in aqueous buffers and can absorb at wavelengths accessible in commercial microarray scanners. The overall method allows sequence-specific detection in a time-efficient and cost-effective process.Note: If the targets used are longer than 40 nt, the hybridization mixture should be heated to 95 °C for 5 min immediately before being loaded to the array. The target concentration can be reduced reliably to 10−7 M.Note: The LifterSlip should be rinsed off from the slide with H2O to avoid scratching the surface of the microarray.Note: For longer targets or for added stringency, washing can be done at 37 °C by preheating the washing solution to 37 °C and shaking in a 37 °C incubator.Slide hydration, Steps 1–6: 25–30 minSample hybridization, Steps 7–12: 30–35 minPost-hybridization wash, Steps 13–19: 15–20 minPolymer application, Steps 20–23: 30 minWash and dry slide after polymer application, Steps 24–27: 5 minThe whole procedure should take between 2.5 and 3 h. Buffer preparation requires additional time.Step 14The post-hybridization wash is highly dependent on the nature of the target. Longer or more complicated targets tend to require longer and higher temperature washes. Increased temperature washes will help to lower background and increase stringency.Polymer binding and thus signal intensities will vary with the degree of hybridization and the quality of slide processing. We suggest starting with a laser power of 90% and varying the PMT gain to maximize the signals while keeping the more intense spots from reaching saturation. If any of the spots are saturated, decrease the PMT power before reducing the laser power.A representative image and related information are shown in Figure 4. The data were acquired by hybridizing a mixture of unlabeled targets (2 × 10−11 mol) to a PNA slide with multiple PNA probes. Each spot has a diameter of ~200 μm.The results provided in Figure 4 represent those obtained using synthetic oligonucleotide targets. These target standards were selected as a means to optimize the overall process. This protocol has been used to successfully detect PCR amplicons (purified using Qiagen spin columns). As expected, higher signals were obtained using the products of asymmetric PCRs, which produce predominantly ssDNA. Like nearly all DNA microarrys, single-stranded targets have been found to hybridize more effectively than double-stranded targets, which can simply re-anneal. This problem is typically more pronounced for longer targets. This protocol is currently being applied in the detection of cDNA (mRNA) derived from pathogenic bacteria. The probe sequences in Figure 4 correspond to segments found in Staphylococcus aureus and Staphylocccus epidermidis.Owing to the intrinsic electrostatic interactions (between target DNA and PFBT) employed in this method, it is critical to reduce or eliminate any unwanted charge on the final detection surface. As such, the buffers provided in this protocol do not contain some of the commonly used blocking reagents, including bovine serum albumin and/or salmon DNA. Charged surfaces (e.g., poly-lysine-coated sides), which require these blocking agents, were also avoided. The presence of any negatively charged blocking agent or nonspecifically bound DNA/RNA on the final surface will increase the nonspecific adsorption of the cationic polymer and thus the overall background observed. High background signals would indicate incomplete washing of the target DNA post-hybridization and/or the polymer post-application. Note that, if the target solution dries during hybridization, it is often difficult to completely remove the nonspecifically bound DNA from the surface. The buffers and protocols provided have been optimized to minimize nonspecific DNA and polymer binding to the array surfaces.Reproducibility is an issue common to nearly all microarray detection formats. Several standard approaches were employed to increase the reliability of the protocol provided. These include (i) following the listed protocol as closely as possible for each experiment, (ii) including both positive and negative controls in each array sample, (iii) using multiple probes and multiple spots (at least five) for each sequence/target and (iv) printing replicates of each subarray.
Co-reporter:Robert C. Coffin, Steve J. Diamanti, Atsushi Hotta, Vikram Khanna, Edward J. Kramer, Glenn H. Fredrickson and Guillermo C. Bazan
Chemical Communications 2007 (Issue 34) pp:3550-3552
Publication Date(Web):31 Jul 2007
DOI:10.1039/B705808J
Pseudo-tetrablock copolymers comprised of ethylene and 5-norbornen-2-yl acetate (1), were synthesized using the initiator system (LiPr2)Ni(η1-CH2Ph)(PMe3) (2) [(LiPr2) = N-(2,6-diisopropylphenyl)-2-(2,6-diisopropylphenylimino)propanamide] and 2.5 equivalents of Ni(COD)2 [bis(1,5-cyclooctadiene) nickel.
Co-reporter:Bin Liu
Macromolecular Rapid Communications 2007 Volume 28(Issue 17) pp:1804-1808
Publication Date(Web):21 AUG 2007
DOI:10.1002/marc.200700344
Efficient energy transfer between a cationic poly(fluorene-co-phenylene) and thiazole orange mediated by a G-rich oligonucleotide provided sensitized TO emission over 25 000-fold more intense than that from free TO. Higher energy transfer efficiency to ssDNA/TO relative to dsDNA/TO leads to an improved sensitivity and selectivity in G-rich DNA hybridization detection as compared to the direct use of TO as the signal reporter. The signal amplification provided by conjugated polymers is useful to amplify the response from other TO-based detection protocols.
Co-reporter:Bin Liu ;Guillermo C. Bazan
Chemistry – An Asian Journal 2007 Volume 2(Issue 4) pp:499-504
Publication Date(Web):15 MAR 2007
DOI:10.1002/asia.200600257
A cationic water-soluble conjugated polyelectrolyte, poly[9,9-bis(6′′-(N,N,N-trimethylammonium)hexyl)fluorene-co-alt-2,5-bis(6′-(N,N,N-trimethylammonium)hexyloxyphenylene) tetrabromide], was synthesized. Fluorescence resonant energy transfer (FRET) experiments between the polymer and fluorescein-labeled single-stranded DNA (ssDNA-Fl) were conducted in aqueous buffer and THF/buffer mixtures. Weak fluorescence emission in aqueous buffer was observed upon excitation of the polymer, whereas addition of THF turned on the fluorescence. Fluorescence self-quenching of ssDNA-Fl in the ssDNA-Fl/polymer complexes as well as electron transfer from the polymer to fluorescein may account for the low fluorescence emission in buffer. The improved sensitization of fluorescence by the polymer observed in THF/buffer could be attributed to the weaker binding between the polymer and ssDNA-Fl and a decrease in dielectric constant of the solvent mixture, which disfavors electron transfer. THF-assisted signal sensitization was also observed for the polymer and fluorescein-labeled double-stranded DNA (dsDNA-Fl). These results indicate that the use of cosolvent provides a strategy to improve the detection sensitivity for biosensors based on the optical amplification provided by conjugated polymers.
Co-reporter:Y. Tang;F. He;S. Wang;Y. Li;D. Zhu;G. C. Bazan
Advanced Materials 2006 Volume 18(Issue 16) pp:2105-2110
Publication Date(Web):25 JUL 2006
DOI:10.1002/adma.200501534
Information processing by integrated logic gates capable of YES, NOT, AND, NAND, INH, and INHIBIT operations can be simulated using fluorescence resonance energy transfer (FRET) in cationic conjugated polymer/DNA/ ethidium bromide (EB) intercalating-dye assemblies. Additionally, a reversible XNOR logic gate can be designed and implemented with these materials. The figure shows the scheme for the INHIBIT logic gate.
Co-reporter:J. W. Hong;W. L. Hemme;M. T. Rinke;G. E. Keller;G. C. Bazan
Advanced Materials 2006 Volume 18(Issue 7) pp:
Publication Date(Web):24 MAR 2006
DOI:10.1002/adma.200690030
A water soluble cationic conjugated polymer that changes emission color from blue to green when going from dilute to concentrated conditions has been designed in work reported by Bazan and co-workers on p. 878. Electrostatic complexation with anionic double- or single-stranded DNA results in an increase of the local concentration of the conjugated polymer. The resulting changes in the emission spectra can be analyzed to provide an accurate determination of DNA concentration.
Co-reporter:J. W. Hong;W. L. Hemme;G. E. Keller;M. T. Rinke;G. C. Bazan
Advanced Materials 2006 Volume 18(Issue 7) pp:878-882
Publication Date(Web):6 MAR 2006
DOI:10.1002/adma.200501605
Precise determination of DNA concentration without the health risks of intercalating dyes is possible via the optical changes that arise from DNA-induced aggregation of cationic conjugated polyelectrolytes. Addition of DNA to a conjugated electrolyte containing two fluorophores results in aggregation and fluorescence quenching, inducing a measurable and quantifiable shift from blue- to green-light emission (see figure and inside cover).
Co-reporter:D. S. Seferos;R. Y. Lai;K. W. Plaxco;G. C. Bazan
Advanced Functional Materials 2006 Volume 16(Issue 18) pp:
Publication Date(Web):3 NOV 2006
DOI:10.1002/adfm.200500902
While thioacetate-terminated oligo(phenylene vinylene)s (OPVs) have been synthesized and employed in applications involving the formation of metal–molecule–metal junctions, the synthesis and application of potentially more versatile α,ω-dithiol OPVs have not previously been described. Here, a thiomethyl-precursor route to the synthesis of α,ω-dithiol OPVs is reported and their ability to form well-ordered self-assembled monolayers (SAMs) without the addition of exogenous deprotection reagents is described. α,ω-Dithiol OPV monolayers exhibit thicknesses consistent with molecular length and are nearly defect-free, as assayed by electrochemical measurements. To demonstrate the ease with which SAMs containing these bifunctional OPVs can, in contrast to thioacetate functionalized OPVs, be further functionalized with materials other than gold, we have modified them in a single step with a sub-monolayer of cadmium selenide nanocrystals (NCs). Scanning electron microscopy (SEM) and atomic force microscopy (AFM) confirm that these NC-modified films are both smooth and uniform over the largest areas investigated (> 10 μm2) and no evidence of NC aggregation is observed. To evaluate the electrochemical response of these metal–molecule–semiconductor assemblies we have fabricated NC-modified OPV SAMs with ferrocene-coated NCs. Variable-frequency alternating current voltammetry indicates that electron transfer in these assemblies is much more rapid than in analogous structures formed using simple alkane dithiols. It thus appears that α,ω-dithiol OPVs are well suited for the formation of high-quality conducting SAMs for the functionalization of gold and other surfaces.
Co-reporter:X. Gong;S. Wang;D. Moses;G. C. Bazan;A. J. Heeger
Advanced Materials 2005 Volume 17(Issue 17) pp:
Publication Date(Web):29 AUG 2005
DOI:10.1002/adma.200590088
White-light-emitting polymer diodes can be fabricated by solution processing using a blend of luminescent semiconducting polymers and organometallic complexes as the emission layer, and water-soluble (or ethanol-soluble) polymers and/or small molecules as the hole-injection/transport layer (HIL/HTL) and the electron injection/transport layer (EIL/ETL), as reported on p. 2053 by Gong, Bazan, Heeger and co-workers. Illumination-quality light is obtained from these multilayer, high-performance devices, with stable CIE coordinates, color temperatures, and high color-rendering indices all close to those of “pure” white light. The cover illustration envisages the incorporation of the fabrication technique with low-cost manufacturing technology in order to produce large areas of high-quality white light.
Co-reporter:X. Gong;S. Wang;D. Moses;G. C. Bazan;A. J. Heeger
Advanced Materials 2005 Volume 17(Issue 17) pp:
Publication Date(Web):12 JUL 2005
DOI:10.1002/adma.200500727
White-light-emitting polymer diodes containing hole-injection/transport and electron-injection/transport layers have been fabricated by solution processing. Illumination-quality light is obtained from these multilayer, high-performance devices, with stable Commission Internationale d'Eclairage coordinates, stable color temperatures, and stable, high color-rendering indices, which are all close to those of “pure” white light indicated by the dotted oval in the Figure.
Co-reporter:W. Ma;P. K. Iyer;X. Gong;B. Liu;D. Moses;G. C. Bazan;A. J. Heeger
Advanced Materials 2005 Volume 17(Issue 3) pp:
Publication Date(Web):4 FEB 2005
DOI:10.1002/adma.200400963
Multilayer polymer light-emitting diodes are made using semiconducting polymers. An emissive polymer layer is cast from solution in an organic solvent, and a water-soluble (or methanol- soluble) conjugated copolymer is used for the electron transport layer (ETL) in the following device configuration: (indium tin oxide)/poly(3,4-ethylenedioxythiophene)/emissive polymer/ETL/Ba/Al. Devices with an ETL have significantly lower turn-on voltages, higher brightness values, and improved luminous efficiencies.
Co-reporter:Julia-Christina Wasilke;Joseph W. Ziller;Guillermo C. Bazan
Advanced Synthesis & Catalysis 2005 Volume 347(Issue 2-3) pp:
Publication Date(Web):14 FEB 2005
DOI:10.1002/adsc.200404254
The reaction of NiCl2(PMe3)2 with 2 equivs. of benzylmagnesium chloride in THF at −120 °C affords Ni(η1-CH2C6H5)(η3-CH2C6H5)PMe3. The formation of this thermally unstable compound is accompanied by bisbenzyl and Ni(0) side products. Single crystal X-ray analysis confirms the presence of the η1-benzyl and η3-benzyl ligands. Reaction of Ni(η1-CH2C6H5)(η3-CH2C6H5)PMe3 with 2-(diphenylphosphino)benzoic acid and activation with B(C6F5)3 gave the expected product [2-(diphenylphosphino)benzoate tris(pentafluorophenyl)borate-κ2P,O](η3-benzyl)nickel.
Co-reporter:Yaofeng Chen Dr.;Gang Wu Dr. Dr.
Angewandte Chemie International Edition 2005 Volume 44(Issue 7) pp:
Publication Date(Web):12 JAN 2005
DOI:10.1002/anie.200461630
Remote control: A novel molecular design is described and used to probe the activation of transition-metal-based ethylene polymerization and oligomerization initiators by the action of a Lewis acid across an electronically delocalized structural unit. Compound 1 which has a Lewis acid attached to a site removed from the trajectory of the incoming substrate, shows high activity for ethylene oligomerization.
Co-reporter:Dwight S. Seferos;Scott A. Trammell;James G. Kushmerick
PNAS 2005 102 (25 ) pp:8821-8825
Publication Date(Web):2005-06-21
DOI:10.1073/pnas.0500002102
Charge transport characteristics for metal–molecule–metal junctions containing two structurally related π-conjugated systems
were studied to probe π–π interactions in molecular junctions. The first molecule contains a typical π-conjugated framework
derived from phenylene vinylene units, whereas the second has the phenylene vinylene structure interrupted by a [2.2]paracyclophane
(pCp) core. Electrochemical investigations were used to characterize the defects and packing density of self-assembled monolayers
of the two molecules on gold surfaces and to enable quantitative comparison of their transport characteristics. Current–voltage
measurements across molecular junctions containing the two species demonstrate that the pCp moiety yields a highly conductive
break in through-bond π-conjugation. The observed high conductivity is consistent with density functional theory calculations,
which demonstrate strong through-space π–π coupling across the pCp moiety.
Co-reporter:Guillermo C. Bazan;Bin Liu
PNAS 2005 Volume 102 (Issue 3 ) pp:589-593
Publication Date(Web):2005-01-18
DOI:10.1073/pnas.0408561102
A strand-specific DNA sensory method is described based on surface-bound peptide nucleic acids and water-soluble cationic
conjugated polymers. The main transduction mechanism operates by taking advantage of the net increase in negative charge at
the peptide nucleic acid surface that occurs upon single-stranded DNA hybridization. Electrostatic forces cause the oppositely
charged cationic conjugated polymer to bind selectively to the “complementary” surfaces. This approach circumvents the current
need to label the probe or target strands. The polymer used in these assays is poly[9,9′-bis(6′′-N,N,N-trimethylammonium)hexyl)fluorene-co-alt-4,7-(2,1,3-benzothiadiazole) dibromide], which was specifically designed and synthesized to be compatible with excitation
sources used in commonly used DNA microarray readers. Furthermore, the utility of poly[9,9′-bis(6′′-N,N,N-trimethylammonium)-hexyl)fluorene-co-alt-4,7-(2,1,3-benzothiadiazole) dibromide] has been demonstrated in homogenous and solid-state assays that involve fluorescence
resonance energy transfer to a reporter dye (Cy5) and that can benefit from the light harvesting properties observed in water-soluble
conjugated polymers.
Co-reporter:Brent S. Gaylord;Michelle R. Massie;Stuart C. Feinstein;
Proceedings of the National Academy of Sciences 2005 102(1) pp:34-39
Publication Date(Web):December 23, 2004
DOI:10.1073/pnas.0407578101
A strategy employing a combination of peptide nucleic acid (PNA) probes, an optically amplifying conjugated polymer (CP),
and S1 nuclease enzyme is capable of detecting SNPs in a simple, rapid, and sensitive manner. The recognition is accomplished
by sequence-specific hybridization between the uncharged, fluorescein-labeled PNA probe and the DNA sequence of interest.
After subsequent treatment with S1 nuclease, the cationic water soluble CP electrostatically associates with the remaining
anionic PNA/DNA complex, leading to sensitized emission of the labeled PNA probe via FRET from the CP. The generation of fluorescent
signal is controlled by strand-specific electrostatic interactions and is governed by the complementarity of the probe/target
pair. To assess the method, we compared the ability of the sensor system to detect normal, wild-type human DNA sequences,
and those sequences containing a single base mutation. Specifically, we examined a PNA probe complementary to a region of
the gene encoding the microtubule associated protein tau. The probe sequence covers a known point mutation implicated in a
dominant neurodegenerative dementia known as frontotemporal dementia with parkinsonism linked to chromosome 17 (FTDP-17),
which has clinical and molecular similarities to Alzheimer's disease. By using an appropriate PNA probe, the conjugated polymer
poly[(9,9-bis(6′-N,N,N-trimethylammoniumhexylbromide)fluorene)-co-phenylene] and S1 nuclease, unambiguous FRET signaling is achieved for the wild-type
DNA and not the mutant sequence harboring the SNP. Distance relationships in the CP/PNA assay are also discussed to highlight
constraints and demonstrate improvements within the system.
Co-reporter:X. Gong;W. Ma;J. C. Ostrowski;G. C. Bazan;D. Moses;A. J. Heeger
Advanced Materials 2004 Volume 16(Issue 7) pp:
Publication Date(Web):20 APR 2004
DOI:10.1002/adma.200306230
Co-reporter:S. Wang;B. S. Gaylord;G. C. Bazan
Advanced Materials 2004 Volume 16(Issue 23‐24) pp:
Publication Date(Web):16 DEC 2004
DOI:10.1002/adma.200401036
Water-soluble dendrimers containing cationic charges and optically active units on the periphery of the macromolecular structure have been designed. Collective optical behavior of the chromophores on the surface was demonstrated by fluorescence quenching and energy-transfer experiments. These water-soluble dendrimers can be used for optically amplified DNA detection (see Figure) in homogeneous media.
Co-reporter:X. Gong;W. Ma;J. C. Ostrowski;K. Bechgaard;G. C. Bazan;A. J. Heeger;S. Xiao;D. Moses
Advanced Functional Materials 2004 Volume 14(Issue 4) pp:
Publication Date(Web):19 APR 2004
DOI:10.1002/adfm.200305134
The electronic properties, carrier injection, and transport into poly(9,9-dioctylfluorene) (PFO), PFO end-capped with hole-transporting moieties (HTM), PFO–HTM, and PFO end-capped with electron-transporting moieties (ETM), PFO–ETM, were investigated. The data demonstrate that charge injection and transport can be tuned by end-capping with HTM and ETM, without significantly altering the electronic properties of the conjugated backbone. End-capping with ETM resulted in more closely balanced charge injection and transport. Single-layer electrophosphorescent light-emitting diodes (LEDs), fabricated from PFO, PFO–HTM and PFO–ETM as hosts and tris[2,5-bis-2′-(9′,9′-dihexylfluorene)pyridine-κ2NC3′]iridium(III), Ir(HFP)3 as the guest, emitted red light with brightnesses of 2040 cd m–2, 1940 cd m–2 and 2490 cd m–2 at 290 mA cm–2 (16 V) and with luminance efficiencies of 1.4 cd A–1, 1.4 cd A–1 and 1.8 cd A–1 at 4.5 mA cm–2 for PFO, PFO–HTM, and PFO–ETM, respectively.
Co-reporter:Shu Wang and Guillermo C. Bazan
Chemical Communications 2004 (Issue 21) pp:2508-2509
Publication Date(Web):08 Sep 2004
DOI:10.1039/B410002F
The solvent-dependent aggregation properties of a water-soluble cationic poly(fluorene) were studied and used to control fluorescence resonance energy transfer to Texas Red-labeled DNA.
Co-reporter:M.R. Robinson;J.C. Ostrowski;G.C. Bazan;M.D. McGehee
Advanced Materials 2003 Volume 15(Issue 18) pp:
Publication Date(Web):11 SEP 2003
DOI:10.1002/adma.200304651
Co-reporter:S. Wang;G.C. Bazan
Advanced Materials 2003 Volume 15(Issue 17) pp:
Publication Date(Web):1 SEP 2003
DOI:10.1002/adma.200305099
Co-reporter:J.C. Ostrowski;K. Susumu;M.R. Robinson;M.J. Therien;G.C. Bazan
Advanced Materials 2003 Volume 15(Issue 15) pp:
Publication Date(Web):11 AUG 2003
DOI:10.1002/adma.200305228
Co-reporter:X. Gong;J.C. Ostrowski;G.C. Bazan;D. Moses;A.J. Heeger;M.S. Liu;A.K.-Y. Jen
Advanced Materials 2003 Volume 15(Issue 3) pp:
Publication Date(Web):13 FEB 2003
DOI:10.1002/adma.200390063
Co-reporter:X. Gong;J.C. Ostrowski;G.C. Bazan;D. Moses;A.J. Heeger;M.S. Liu;A.K.-Y. Jen
Advanced Materials 2003 Volume 15(Issue 1) pp:
Publication Date(Web):10 JAN 2003
DOI:10.1002/adma.200390007
Co-reporter:H. Benmansour;T. Shioya;Y. Sato;G.C. Bazan
Advanced Functional Materials 2003 Volume 13(Issue 11) pp:
Publication Date(Web):5 NOV 2003
DOI:10.1002/adfm.200304456
Non-crystalline anthracene-containing binaphthol chromophores were synthesized, characterized, and used in the fabrication of organic light-emitting diodes (OLEDs). Specifically, the target molecules were 2,2′-dihexyloxy-1,1′-binaphthol-6,6′-bisanthracene (BA1) and 2,2′-dimethoxyy-1,1′-binaphthol-6,6′-bisanthracene (BA2). Molecules BA1 and BA2 provide amorphous solids, as determined by their glass-transition temperature (Tg) measured by differential scanning calorimetry (DSC). Efficient multilayer OLEDs containing BA1 and BA2 were fabricated by evaporation techniques. Differences in the electroluminescence frequencies of these devices suggests that the degree of alkoxide substitution controls the mobility within the binaphthol material, and therefore the recombination region in the device. Compound BA2 can also be used to dope CBP ((4,4′-bis(carbazol-9-yl)biphenyl)) in the fabrication of highly efficient OLEDs.
Co-reporter:X. Gong;J.C. Ostrowski;D. Moses;G.C. Bazan;A.J. Heeger
Advanced Functional Materials 2003 Volume 13(Issue 6) pp:
Publication Date(Web):5 JUN 2003
DOI:10.1002/adfm.200304334
We report high-efficiency green electrophosphorescent light-emitting diodes obtained by using tris[9,9-dihexyl-2-(phenyl-4′-(-pyridin-2″-yl))fluorene]iridium(III) (Ir(DPPF)3) as the guest, and a blend of poly(vinylcarbazole) (PVK) with 2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazol (PBD) as the host. The electrophosphorescent emission is characteristic of Ir(DPPF)3, with its maximum at 550 nm. An external quantum efficiency of 8 % photons per electron and luminous efficiency of 29 cd A–1, with maximum brightness of 3500 cd m–2, were achieved at 1 wt.-% concentration of Ir(DPPF)3. The devices exhibited no emission from PVK or PBD, even at the lowest concentration of Ir(DPPF)3 (0.1 wt.-%). The results indicate that Förster energy transfer plays a minor role in achieving high efficiencies in these devices. Direct charge trapping appears to be the main operating mechanism.
Co-reporter:S. Wang;B. Liu;B.S. Gaylord;G.C. Bazan
Advanced Functional Materials 2003 Volume 13(Issue 6) pp:
Publication Date(Web):5 JUN 2003
DOI:10.1002/adfm.200304339
An improved synthetic approach was developed for the synthesis of 1,4-bis[9′,9′-bis(6″-(N,N,N-trimethylammonium)-hexyl)-fluoren-2′-yl]benzene tetrabromide (1a), 1,4-bis[9′,9′;9″,9″-tetra(6″′-(N,N,N-trimethylammonium)-hexyl)-7′,2″-bisfluoren-2′-yl] benzene octabromide (1b) and 1,4-bis[9′,9′;9″,9″;9″′,9″′-hexakis(6″″-(N,N,N-trimethylammonium)-hexyl)-7′,2″,7″,2″′-trifluoren-2′-yl] benzene dodecabromide (1c). These molecules provide a size-specific series of water-soluble oligofluorene molecules with increasing numbers of repeat units to model the interactions between cationic conjugated polymers and DNA. Fluorescence quenching and energy-transfer measurements were performed with 1a–c and single-stranded (ss) DNA and double-stranded (ds) DNA, with and without fluorescein (Fl). These studies show that, on a per-negative-charge basis, ssDNA quenches the emission of 1a–c more effectively than dsDNA. Furthermore, we show that the energy-transfer ratios dsDNA–Fl/ssDNA–Fl are dependent on the number of repeat units in 1a–c.
Co-reporter:Zachary J.A Komon, Guillermo C Bazan, Cindy Fang, Xianhui Bu
Inorganica Chimica Acta 2003 Volume 345() pp:95-102
Publication Date(Web):10 March 2003
DOI:10.1016/S0020-1693(02)01345-2
Addition of BF3·Et2O to {[(C6H5)2PC6H4(μ-CO2)-κ3P,O,O′]Ni(η1-CH2C6H5)}2 gives [(C6H5)2PC6H4C(OBF3)O-κ2P,O]Ni(η3-CH2C6H5) (4). The single crystal structure of 4 is consistent with substantial positive charge at the nickel atom. Addition of ethylene to solutions of 4 in toluene provides ethylene oligomers. The average molecular weight of the products is larger than that of the oligomers obtained using [(C6H5)2PC6H4C(OB(C6F5)3)O-κ2P,O]Ni(η3-CH2C6H5) (1). When 2 equiv. of Et2O·BF3 are added to {(H3C)C[N(2,6-(CHMe2)2C6H3)]C(O)[N(2,6-(CHMe2)2C6H3)]-κ2N,O}Ni(η1-CH2C6H5)(PMe3) (5) one obtains {(H3C)C[N(2,6-(CHMe2)2C6H3)]C[OBF3][N(2,6-(CHMe2)2C6H3)]-κ2N,N′}Ni(η3-CH2C6H5) (7). Two isomers of 7 are observed by NMR spectroscopy and are incorporated into the crystal lattice, as shown by X-ray diffraction studies. Polyethylene is obtained upon exposure of a solution of 7 to ethylene. Active species can also be generated in situ by addition of BF3 gas, Et2O·BF3 or tBuMeO·BF3 to 5.BF3 can be used to activate nickel complexes that react with ethylene. Addition of ethylene to compound 4 provides oligomers. Compound 7 is an ethylene polymerization initiator.
Co-reporter:Janice W. Hong;Hadjar Benmansour Dr.
Chemistry - A European Journal 2003 Volume 9(Issue 14) pp:
Publication Date(Web):3 JUL 2003
DOI:10.1002/chem.200304776
Conjugated polymers and oligomers can serve as highly responsive fluorescent reporters for biosensor applications. However, their optical properties in aqueous media are highly dependent upon environmental conditions. The structure of the paracyclophane framework provides a platform for designing optical reporters that show little sensitivity to surfactants, and thus is well-suited for fluorescent assays. The permanent intramolecular delocalization through the paracyclophane core dominates intermolecular perturbations in spontaneously formed aggregates.
Co-reporter:Xiangdong Fang Dr.;David Woodmansee;Xianhui Bu Dr. Dr.
Angewandte Chemie 2003 Volume 115(Issue 37) pp:
Publication Date(Web):25 SEP 2003
DOI:10.1002/ange.200351911
Durch Insertion von Acetylen in eine Ring-B-C-Bindung von [(C5H5BMe)2Ti(CO)] (1) entsteht [(C7H7BMe)(C5H5BMe)Ti]. Dabei wird der formal trianionische Methylboratacyclooctatetraen-Ligand gebildet. Die analoge Reaktion von 1 mit Trimethylsilylacetylen ergibt [(2-SiMe3-C7H6BMe)(C5H5BMe)Ti] (2). Im Produkt befindet sich die Trimethylsilylfunktion in der sterisch ungünstigeren Position an Cα (siehe Bild); daher verläuft die Transmetallierung vermutlich als elektrophiler Angriff des Bors auf den koordinierten Acetylen-Liganden.
Co-reporter:Xiong Gong;Jacek C. Ostrowski;Daniel Moses;Alan J. Heeger
Journal of Polymer Science Part B: Polymer Physics 2003 Volume 41(Issue 21) pp:2691-2705
Publication Date(Web):2 OCT 2003
DOI:10.1002/polb.10645
High-performance electrophosphorescent light-emitting diodes (LEDs) were demonstrated with tris-[9,9-dihexyl-2-(pyridinyl-2′) fluorene] iridium(III) [Ir(DPF)3], tris-{9,9-dihexyl-2-[phenyl-4′-(-pyridin-2″-yl)] fluorene} iridium(III) [Ir(DPPF)3], and tris-[2,5-bis-2′-(9,9′-dihexylfluorene) iridium] [Ir(HFP)3] as guests and poly(vinylcarbazole) (PVK) blended with 2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazol (PBD), poly(9,9-dioctylfluorenyl-2,7-diyl) (PFO), and poly(9,9-dihexylfluorene)-co-2,5-dicyanophenylene (PF3CNP1) as hosts. The devices made with PVK-PBD exhibited the highest external quantum efficiency (QEext), luminous efficiency (LE) and luminance (L). For example, yellowish green emission from PVK-PBD doped with Ir(DPF)3 was observed with QEext = 10% ph/el, LE = 36 cd/A, and L > 8300 cd/m2, and red emission from PVK-PBD doped with Ir(DPPF)3 was observed with QEext = 5% ph/el, LE = 7.2 cd/A, and L > 2700 cd/m2. Red electrophosphorescent LEDs with a low turn-on voltage (5 V), QEext= 4.5% ph/el, LE = 6.2 cd/A, and L > 1000 cd/m2 were achieved with the conjugated polymer, PFO, as the host and Ir(HFP)3 as the guest. Electrophosphorescent LEDs fabricated with the conjugated copolymer PF3CNP1 doped with Ir(HFP)3 exhibited QEext = 1.5% ph/el and LE = 3 cd/A with L = 2200 cd/m2. These devices exhibited good operational stability under DC drive at room temperature. Förster energy transfer played a minor role in achieving the high efficiencies in these electrophosphorescent devices; direct sequential charge trapping appeared to be the main operating mechanism. These results demonstrated that high-performance electrophosphorescence can be obtained from polymer-based LEDs that are fabricated by processing the active materials directly from solution. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2691–2705, 2003
Co-reporter:Xiangdong Fang Dr.;David Woodmansee;Xianhui Bu Dr. Dr.
Angewandte Chemie International Edition 2003 Volume 42(Issue 37) pp:
Publication Date(Web):25 SEP 2003
DOI:10.1002/anie.200351911
Expanding the ring: Acetylene inserts into one of the intracyclic BC bonds of [(C5H5BMe)2Ti(CO)] (1) to yield [(C7H7BMe)(C5H5BMe)Ti], which contains the formally trianionic methylboratacyclooctatetraene ligand and a boratabenzene ligand. Similarly, the reaction of 1 with trimethylsilylacetylene produces [(2-SiMe3C7H6BMe)(C5H5BMe)Ti] (2), in which the trimethylsilyl group occupies the sterically more encumbering site adjacent to boron (Cα; see picture). The regiochemistry of 2 indicates that the transmetallation step may be viewed as an electrophilic attack of boron on the metal coordinated acetylene ligand.
Co-reporter:M. Stork;B.S. Gaylord;A.J. Heeger;G.C. Bazan
Advanced Materials 2002 Volume 14(Issue 5) pp:
Publication Date(Web):28 FEB 2002
DOI:10.1002/1521-4095(20020304)14:5<361::AID-ADMA361>3.0.CO;2-9
Co-reporter:X. Gong;M.R. Robinson;J.C. Ostrowski;D. Moses;G.C. Bazan;A.J. Heeger
Advanced Materials 2002 Volume 14(Issue 8) pp:
Publication Date(Web):18 APR 2002
DOI:10.1002/1521-4095(20020418)14:8<581::AID-ADMA581>3.0.CO;2-B
Co-reporter:Jacek C. Ostrowski, Matthew R. Robinson, Alan J. Heeger and Guillermo C. Bazan
Chemical Communications 2002 (Issue 7) pp:784-785
Publication Date(Web):14 Mar 2002
DOI:10.1039/B200957A
Iridium complexes with fluorene-modified phenylpyridine ligands are resistant to crystallization and can be used in the fabrication of single layer light emitting diodes.
Co-reporter:Guillermo C. Bazan;Alan J. Heeger;Brent S. Gaylord
PNAS 2002 Volume 99 (Issue 17 ) pp:10954-10957
Publication Date(Web):2002-08-20
DOI:10.1073/pnas.162375999
The light-harvesting properties of cationic conjugated polymers are used to sensitize the emission of a dye on a specific
peptide nucleic acid (PNA) sequence for the purpose of homogeneous, “real-time” DNA detection. Signal transduction is controlled
by hybridization of the neutral PNA probe and the negative DNA target. Electrostatic interactions bring the hybrid complex
and cationic polymer within distances required for Förster energy transfer. Conjugated polymer excitation provides fluorescein
emission >25 times higher than that obtained by exciting the dye, allowing detection of target DNA at concentrations of 10
pM with a standard fluorometer. A simple and highly sensitive assay with optical amplification that uses the improved hybridization
behavior of PNA/DNA complexes is thus demonstrated.
Co-reporter:M. R. Robinson;S. Wang;A. J. Heeger;G. C. Bazan
Advanced Functional Materials 2001 Volume 11(Issue 6) pp:
Publication Date(Web):6 DEC 2001
DOI:10.1002/1616-3028(200112)11:6<413::AID-ADFM413>3.0.CO;2-C
Tetrakis[(4-(4′-(2″,5″-dioctyloxy-4″-(4‴-(2′‴,5′‴-dioctyloxy-4′‴-styryl)styryl)styryl)styryl)styryl)phenyl]methane (T-6R-OC8H17) is an organic chromophore that consists of four optoelectronic fragments (“arms”) connected to a tetrahedral point of convergence (carbon). Bulk samples are amorphous as determined by powder diffraction, while differential scanning calorimetry (DSC) is sometimes ambiguous. Film forming properties were studied by atomic force microscopy (AFM) and fluorescence microscopy as a function of casting solvent and heat treatment. The film forming qualities are useful for the fabrication of light-emitting diodes with low turn-on voltages. Device performance is also history dependent. The relationship between bulk morphology, film topology, photoluminescence (PL) properties, and light-emitting diode (LED) performance is discussed. A comparison of these compounds against the parent oligo(phenylenevinylene) arms, with respect to morphology, topology, and PL properties is also presented.
Co-reporter:David H. Woodmansee, Xianhui Bu and Guillermo C. Bazan
Chemical Communications 2001 (Issue 7) pp:619-620
Publication Date(Web):13 Mar 2001
DOI:10.1039/B009246K
Reaction of Li[C5H5B–Ph] with
[RhCl(C2H4)2]2 gives
[C5H5B–Ph]Rh(C2H4)2
1 in 91% yield; similarly,
Li[C5H5B–NMe2] with
[RhCl(C2H4)2]2 gives
[C5H5B–NMe2]Rh(C2H4
)2 2 in 85% yield; single crystal X-ray analysis studies
of 1 and 2 show a molecular geometry analogous to those of the Cp and Cp*
complexes; the use of 1 and 2 in promoting alkane boration was evaluated
against the activity of Cp*Rh(C2H4)2 3;
the boratabenzene complexes 1 and 2 show faster initiation, but yield less
thermally stable catalysts than 3.
Co-reporter:Jacek C. Ostrowski;Raymond A. Hudack, Jr.;Matthew R. Robinson;Shujun Wang Dr.
Chemistry - A European Journal 2001 Volume 7(Issue 20) pp:
Publication Date(Web):5 OCT 2001
DOI:10.1002/1521-3765(20011015)7:20<4500::AID-CHEM4500>3.0.CO;2-V
The use of the binaphthyl framework to synthesize glass-forming organic chromophores is described. Suzuki coupling reactions of racemic 6,6′-dibromo-2,2′-dialkoxy-1,1′-binaphthyl with 1,1-diphenyl-2-(4-dihydroxyboronphenyl)-ethene using [Pd(dppf)Cl2] (dppf=1,1′-bis(diphenylphosphino)ferrocene) as the catalyst provide a set of chromophores with the 4-(2,2′-diphenylvinyl)-1-phenyl group at the 6- and 6′-positions and a range of groups on the oxygen atom. Starting with enantiomerically enriched (R)-6,6′-dibromo-2,2′-dihexyloxy-1,1′-binaphthyl ((R)-2Hex), one can obtain (R)-3Hex. Heck coupling reactions of 6,6′-dibromo-2,2′-dialkoxy-1,1′-binaphthyl compounds with styrene provide chromophores of the type 2,2′-dialkoxy-1,1′-binaphthyl-6,6′-bis(2-phenyl-vinyl). Starting with enantiomerically enriched (R)-2Hex, one obtains (R)-4Hex. Molecules of the type 4 contain two 1-naphthyl-2-phenyl ethylene chromophores with a pseudo-orthogonal relationship. Similar procedures can be used to obtain fragments with more extended conjugation length. Thus, the Heck coupling reaction of 2Hex with 4-(4′-tert-butylstyryl)styrene, 1-(4′-tert-butylstyryl)-4-(4′-vinylstyryl)benzene, and 1-(3′,5′-dihexyloxystyryl)-4-(4′-vinylstyryl)benzene provides 5Hex, 6Hex, and 7Hex, respectively. DSC measurements and powder diffraction experiments indicate that the binaphthol chromophores show a resistance to crystallization. In some cases, considerably different thermal behavior is observed between enantiomerically enriched samples and their racemic counterparts. Increasing the size of the conjugated fragment on the binaphthol core leads to materials with higher glass-transition temperatures and a less pronounced tendency to crystallize. Fluorescence spectroscopy gives evidence of “excimer”-type interactions in the solid state, except for the chromophores with 4-(2,2′-diphenylvinyl)-1-phenyl groups. It is possible to obtain amorphous films of these chromophores directly from solution, and to fabricate light-emitting diodes, in which the electroluminescent layer corresponds to the binaphthyl chromophore.
Co-reporter:Jung Hwa Seo ; Andrea Gutacker ; Bright Walker ; Shinuk Cho ; Andres Garcia ; Renqiang Yang ; Thuc-Quyen Nguyen ; Alan J. Heeger
Journal of the American Chemical Society () pp:
Publication Date(Web):December 7, 2009
DOI:10.1021/ja908441c
To improve injection in n-type organic thin film transistors (OTFTs), a thin conjugated polyelectrolyte (CPE) layer was interposed between electrodes and the semiconductor layer. OTFTs were fabricated with [6,6]-phenyl-C61 butyric acid methyl ester (PCBM) and Au source and drain contacts. We demonstrate that the insertion of CPEs beneath top-contact Au source/drain electrodes can be a very effective strategy for improving the carrier injection and reducing turn-on threshold voltages of n-channel OTFTs. Ultraviolet photoemission spectroscopy (UPS) indicates that the decrease of the electron injection barrier is consistent with organized dipoles at the metal/organic interface.
Co-reporter:Nan Hu, Cheng-Kang Mai, Glenn H. Fredrickson and Guillermo C. Bazan
Chemical Communications 2016 - vol. 52(Issue 11) pp:NaN2240-2240
Publication Date(Web):2015/11/30
DOI:10.1039/C5CC09200K
A simple, one-pot approach to synthesize random semicrystalline/amorphous multiblock copolymers (12–17 blocks per chain on average) is demonstrated that takes advantage of acyclic diene metathesis (ADMET) polymerization of α,ω-divinyl-terminated telechelic polyolefins. This synthetic approach offers a generic, viable and economical route to polyolefin-based multiblock copolymers and may be extendable to broader families of multiblock materials.
Co-reporter:Ming Wang, Michael Ford, Hung Phan, Jessica Coughlin, Thuc-Quyen Nguyen and Guillermo C. Bazan
Chemical Communications 2016 - vol. 52(Issue 15) pp:NaN3210-3210
Publication Date(Web):2016/01/19
DOI:10.1039/C5CC10009G
Four conjugated copolymers with a donor/acceptor architecture comprising 4,4-dihexadecyl-4H-cyclopenta[1,2-b:5,4-b′]dithiophene as the donor structural unit and benzo[2,1,3]thiadiazole fragments with varying degrees of fluorination as the acceptor structural units have been synthesized and characterized. It has been shown that the energy levels were decreased after the fluorine substitution. The field-effect charge carrier mobility was similar for all polymers with less than an order of magnitude difference between different acceptor units.
Co-reporter:A. W. Thomas, C. Catania, L. E. Garner and G. C. Bazan
Chemical Communications 2015 - vol. 51(Issue 45) pp:NaN9297-9297
Publication Date(Web):2015/05/01
DOI:10.1039/C5CC01724F
Conjugated oligoelectrolytes (COEs) bearing pyridinium and carboxylate groups are synthesized, characterized, and compared to the trimethylammonium analogue from which they are derived. All COEs are able to spontaneously intercalate into liposomes, whereas only positively charged COEs intercalate into E. coli membranes. Membrane intercalation is determined necessary for performance enhancement in microbial fuel cells.
Co-reporter:Paulina Gwozdzinska, Roza Pawlowska, Justyna Milczarek, Logan E. Garner, Alexander W. Thomas, Guillermo C. Bazan and Arkadiusz Chworos
Chemical Communications 2014 - vol. 50(Issue 94) pp:NaN14861-14861
Publication Date(Web):2014/10/07
DOI:10.1039/C4CC06478J
Conjugated phenylenevinylene oligoelectrolytes, which consist of a phenylenevinylene core equipped at each end with hydrophilic pendent groups, are shown to be good candidates for mammalian cell membrane staining. When used in the micromolar concentration range, they express low to moderate cell toxicity for selected regular and cancerous cell lines as tested for adherent and suspension cells.
Co-reporter:Nekane Guarrotxena and Guillermo C. Bazan
Chemical Communications 2011 - vol. 47(Issue 31) pp:NaN8786-8786
Publication Date(Web):2011/07/07
DOI:10.1039/C1CC12659H
Protein detection at the femtomolar level can be achieved by using metallic nanoparticle assemblies that function as surface enhanced Raman spectroscopy reporters and that contain suitable surface-bound recognition elements. Proper control of the interaction between nanoparticles within the assemblies is critical for achieving this performance.
Co-reporter:Hengjing Yan, Zachary D. Rengert, Alexander W. Thomas, Carolin Rehermann, Jamie Hinks and Guillermo C. Bazan
Chemical Science (2010-Present) 2016 - vol. 7(Issue 9) pp:NaN5722-5722
Publication Date(Web):2016/06/01
DOI:10.1039/C6SC00630B
Conjugated oligoelectrolytes (COEs) with phenylenevinylene (PV) repeat units are known to spontaneously intercalate into cell membranes. Twelve COEs, including seven structures reported here for the first time, were investigated for the relationship between their membrane disrupting properties and structural modifications, including the length of the PV backbone and the presence of either a tetraalkylammonium or a pyridinium ionic pendant group. Optical characteristics and interactions with cell membranes were determined using UV-Vis absorption and photoluminescence spectroscopies, and confocal microscopy. Toxicity tests on representative Gram-positive (Enterococcus faecalis) and Gram-negative (Escherichia coli) bacteria reveal generally greater toxicity to E. faecalis than to E. coli and indicate that shorter molecules have superior antimicrobial activity. Increased antimicrobial potency was observed in three-ring COEs appended with pyridinium ionic groups but not with COEs with four or five PV repeat units. Studies with mutants having cell envelope modifications indicate a possible charge based interaction with pyridinium-appended compounds. Fluorine substitutions on COE backbones result in structures that are less toxic to E. coli, while the addition of benzothiadiazole to COE backbones has no effect on increasing antimicrobial function. A weakly membrane-intercalating COE with only two PV repeat units allowed us to determine the synthetic limitations as a result of competition between solubility in aqueous media and association with cell membranes. We describe, for the first time, the most membrane disrupting structure achievable within two homologous series of COEs and that around a critical three-ring backbone length, structural modifications have the most effect on antimicrobial activity.
Co-reporter:Jason D. Azoulay;Yanika Schneider;Griselda B. Galland
Chemical Communications 2009(Issue 41) pp:NaN6179-6179
Publication Date(Web):2009/10/13
DOI:10.1039/B912743G
A nickel α-keto-β-diimine initiator can be activated using treated methylaluminoxane (MAO) to generate active sites capable of the polymerization of ethylene, propene and 1-hexene under living conditions.
Co-reporter:Ji-Eun Jeong, Boram Kim, Shinjae Woo, Sungu Hwang, Guillermo C. Bazan and Han Young Woo
Chemical Science (2010-Present) 2015 - vol. 6(Issue 3) pp:NaN1894-1894
Publication Date(Web):2015/01/07
DOI:10.1039/C4SC03258F
A strategy to extend the detection range of weakly-binding targets is reported that takes advantage of fluorescence resonance energy transfer (FRET)-based bioassays based on molecular beacon aptamers (MBAs) and cationic conjugated polyelectrolytes (CPEs). In comparison to other aptamer-target pairs, the aptamer-based adenosine triphosphate (ATP) detection assays are limited by the relatively weak binding between the two partners. In response, a series of MBAs were designed that have different stem stabilities while keeping the constant ATP-specific aptamer sequence in the loop part. The MBAs are labeled with a fluorophore and a quencher at both termini. In the absence of ATP, the hairpin MBAs can be opened by CPEs via a combination of electrostatic and hydrophobic interactions, showing a FRET-sensitized fluorophore signal. In the presence of ATP, the aptamer forms a G-quadruplex and the FRET signal decreases due to tighter contact between the fluorophore and quencher in the ATP/MBA/CPE triplex structure. The FRET-sensitized signal is inversely proportional to [ATP]. The extension of the detection range is determined by the competition between opening of the ATP/MBA G-quadruplex by CPEs and the composite influence by ATP/aptamer binding and the stem interactions. With increasing stem stability, the weak binding of ATP and its aptamer is successfully compensated to show the resistance to disruption by CPEs, resulting in a substantially broadened detection range (from millimolar up to nanomolar concentrations) and a remarkably improved limit of detection. From a general perspective, this strategy has the potential to be extended to other chemical- and biological-assays with low target binding affinity.
Co-reporter:Robert C. Coffin, Steve J. Diamanti, Atsushi Hotta, Vikram Khanna, Edward J. Kramer, Glenn H. Fredrickson and Guillermo C. Bazan
Chemical Communications 2007(Issue 34) pp:NaN3552-3552
Publication Date(Web):2007/07/31
DOI:10.1039/B705808J
Pseudo-tetrablock copolymers comprised of ethylene and 5-norbornen-2-yl acetate (1), were synthesized using the initiator system (LiPr2)Ni(η1-CH2Ph)(PMe3) (2) [(LiPr2) = N-(2,6-diisopropylphenyl)-2-(2,6-diisopropylphenylimino)propanamide] and 2.5 equivalents of Ni(COD)2 [bis(1,5-cyclooctadiene) nickel.
Co-reporter:Stephanie L. Fronk, Ming Wang, Michael Ford, Jessica Coughlin, Cheng-Kang Mai and Guillermo C. Bazan
Chemical Science (2010-Present) 2016 - vol. 7(Issue 8) pp:NaN5321-5321
Publication Date(Web):2016/05/03
DOI:10.1039/C6SC00908E
Two narrow bandgap conjugated polymers containing chiral 2-ethylhexyl side chains were synthesized: poly[(4,4-bis(2-ethylhexyl)cyclopenta-[2,1-b:3,4-b′]dithiophene)-2,6-diyl-alt-(2,1,3-benzothiadiazole)-4,7-diyl] (PCPDTBT*) and poly[(4,4-bis(2-ethylhexyl)cyclopenta[2,1-b:3,4-b0]dithiophene)-2,6-diyl-alt-[1,2,5]-thiadiazolo[3,4-c]pyridine] (PCDTPT*). The presence of a chiral substituent provides a handle to study the geometry of interchain aggregates and/or the secondary structure of these conjugated polymers in solution and in thin films via circular dichroism (CD) spectroscopy, provided that the asymmetry in the side-chain is translated to the optically active conjugated backbone. CD signals are observed for PCPDTBT* and PCDTPT* in poor solvent systems, which indicate the presence of chiral ordering in the aggregates. PCPDTBT* shows greater chiral order than PCDTPT* based on their relative anisotropy factors. Additionally, GIWAXS analysis reveals that PCPDTBT* films are more ordered than what is observed for the same polymer containing racemic 2-ethylhexyl chains. Upon solution deposition, the chiral ordering is found to translate to the solid-state microstructure for PCPDTBT* but not PCDTPT*. The presence of a pyridyl nitrogen on the thiadiazolo[3,4-c]pyridine ring of PCDTPT* favors a planar conformation for the backbone such that it has a higher rotational barrier compared to PCPDTBT*. This larger rotational barrier appears to limit the ability of PCDTPT* to adopt a helical structure or relevant chain distortions for achieving chiral aggregates.
Co-reporter:Bruno Grimm, Chad Risko, Jason D. Azoulay, Jean-Luc Brédas and Guillermo C. Bazan
Chemical Science (2010-Present) 2013 - vol. 4(Issue 4) pp:NaN1819-1819
Publication Date(Web):2013/02/06
DOI:10.1039/C3SC22188A
We discuss donor–acceptor conjugated polymers where the acceptor moieties are orthogonal to the donor-based backbone direction through the synthesis and study of a new class of materials (including six oligomers and three polymers) based on 4H-cyclopentadithiophene (CPDT) with an imine functionality introduced at the CPDT bridgehead position. Absorption spectroscopy provides information on the influence of structure on the optical properties. We paid special attention to the energies and oscillator strengths of the low-energy transitions and how they correlate with chain length. When the orthogonally conjugated materials are compared to a more traditional polymer, where the donor and acceptor fragments are in series along the backbone direction, fundamental differences in the optical properties are observed. Quantum-mechanical studies of the geometric structure, electronic structure, and excited-state vertical transitions using density functional theory unravel the interplay of structural design and resulting optoelectronic properties. Our findings underline that the magnitude and orientation relative to the backbone long axis of the transition dipole moment is key in designing narrow optical-gap materials with large absorption cross-sections and oscillator strengths.
Co-reporter:Wei Lin Leong, Gregory C. Welch, Loren G. Kaake, Christopher J. Takacs, Yanming Sun, Guillermo C. Bazan and Alan J. Heeger
Chemical Science (2010-Present) 2012 - vol. 3(Issue 6) pp:NaN2109-2109
Publication Date(Web):2012/03/26
DOI:10.1039/C2SC20157G
The final step in the preparation of ppp-DTS(PTTh222)222 involves end capping of the PT-DTS-PT core with 2-hexylbithiophene units via a microwave assisted Stille cross coupling reaction. Methyl transfer (instead of 2-hexylbithiophene transfer) can occur leading to the formation of (MePT)DTS(PTTh22). Although (MePT)DTS(PTTh22) is difficult to separate from the ppp-DTS(PTTh222)222 product via column chromatography, it is readily extracted using hexanes solvent to give absolute ppp-DTS(PTTh222)222. Trace impurities of (MePT)DTS(PTTh22) in BHJ solar cells fabricated from synthesis batches of ppp-DTS(PTTh222)222 significantly influence the photovoltaic properties, causing a ∼50% reduction in efficiency and affecting all of the relevant device parameters (Jsc, Voc and FF). From a broader perspective, despite molecular design, the suitability of a material for efficient devices is often only determined by trial and error in the device processing laboratory. As shown by the data presented in this publication, promising materials found to be unsuitable for device applications may suffer from highly dilute impurities that act to increase carrier recombination.
Co-reporter:Guangxue Feng, Cheng-Kang Mai, Ruoyu Zhan, Guillermo C. Bazan and Bin Liu
Journal of Materials Chemistry A 2015 - vol. 3(Issue 37) pp:NaN7346-7346
Publication Date(Web):2015/08/06
DOI:10.1039/C5TB01118C
We report the demonstration of antimicrobial conjugated polyelectrolytes (CPEs) with high NIR absorbance for selective and efficient photothermal killing of bacteria over mammalian cells. The antimicrobial CPE possessing quaternary ammonium (QA) terminated side chains (P1) shows higher binding preference and increased dark toxicity towards Gram-positive and Gram-negative bacteria over mammalian cells. Bestowed by π-conjugated backbones, P1 exhibits a high molar absorptivity of 39.8 L g−1 cm−1 at 808 nm with an efficient photothermal conversion efficiency of 33 ± 1%. Upon 808 nm laser irradiation, P1 shows enhanced bactericidal effects, but not to mammalian cells. Although the anionic CPE counterpart with the same polymer backbone but sulfonate terminated side chains (P2) possesses a similar photothermal conversion ability, it exhibits much lower antibacterial effects due to its low binding affinity. This study thus reveals that bacteria–CPE electrostatic interactions play a major role in bacterial recognition, although hydrophobic interactions also contribute.
Co-reporter:Yeong Don Park, Jin Kuen Park, Wi Hyoung Lee, Boseok Kang, Kilwon Cho and Guillermo C. Bazan
Journal of Materials Chemistry A 2012 - vol. 22(Issue 23) pp:NaN11465-11465
Publication Date(Web):2012/04/24
DOI:10.1039/C2JM31183F
By dipping into hexane, it is possible to efficiently eliminate the low MW component and also improve the molecular ordering of a conjugated polymer thin film. These changes improve the performance of field-effect transistors. The correlation between the nanoscalar structural features and the electrical properties enables us to determine both the appropriate dipping time and how the low MW component influences electronic properties.
Co-reporter:Nam Sung Cho, Sang Kyu Lee, Jung Hwa Seo, Mark Elbing, Jason D. Azoulay, Juhyun Park, Shinuk Cho, Alan J. Heeger and Guillermo C. Bazan
Journal of Materials Chemistry A 2008 - vol. 18(Issue 41) pp:NaN4911-4911
Publication Date(Web):2008/09/29
DOI:10.1039/B813051E
α,ω-Dihexylthienoselenophenes (Se2Thx) are readily prepared oligomeric species that can be used as the semiconducting layer in organic thin film transistors (TFTs). These selenophene-containing oligomers exhibit high hole mobilities (0.023 and 0.16 cm2 V−1 s−1) and good on/off ratio (105–106) that are improved relative to their sulfur-containing counterparts. X-Ray diffraction measurements and atomic force microscopy give insight into the internal structure and surface topography of the materials.
Co-reporter:Andreas Lorbach, Emily Maverick, Abel Carreras, Pere Alemany, Guang Wu, Miguel A. Garcia-Garibay and Guillermo C. Bazan
Physical Chemistry Chemical Physics 2014 - vol. 16(Issue 25) pp:NaN12986-12986
Publication Date(Web):2014/05/22
DOI:10.1039/C4CP01036A
A new fullerene structure was recently obtained from the reaction of a Lewis basic N-heterocyclic carbene (NHC) and the Lewis acidic C60. The molecular features of the zwitterionic adduct can be described as a molecular rotor with the fullerene cage acting as the rotator that spins about one distinct axis given by its C–C single bond linkage with the imidazolium heterocycle stator. A detailed structural analysis of the compound by means of single-crystal X-ray diffraction (XRD) revealed significant differences in the packing motifs of solvent-free and solvent-containing crystals. Variable temperature single-crystal XRD experiments (80 K ≤ T ≤ 480 K) carried out to investigate the rotational dynamics of the fullerene group in the higher quality solvent-free structure revealed atomic displacement parameters consistent with fast rotation of the highly symmetric fullerene in the solid state, whereas the imidazolium unit remains in a fixed position and therefore represents the stator. DFT and semiempirical calculations were applied to get insight into the profile of the rotational potential of the fullerene unit, particularly considering interactions with the neighboring molecules in the crystal lattice. The results indicate that the crystal environment leads to the presence of one lowest energy minimum that is connected to seven others that are slightly higher in energy through rotational barriers of approximately 1.5–2.5 kcal mol−1.
Co-reporter:Jianyu Yuan, Michael Ford, Guanqun Ding, Huilong Dong, Ming Wang, Lu Han, Youyong Li, Guillermo C. Bazan and Wanli Ma
Journal of Materials Chemistry A 2016 - vol. 4(Issue 44) pp:NaN17343-17343
Publication Date(Web):2016/10/11
DOI:10.1039/C6TA07201A
In this contribution, starting from a high mobility polymer P2 with a regioregular D–A–D–A structure, we set out to further optimize the optical bandgap and energy levels for photovoltaic applications. By introducing different donor segments to construct a modified D′–A–D–A backbone, we successfully synthesized three polymers named as PBT, PFT and PPT. Our results demonstrate that the rotation barrier between the D′ and A or D and A significantly increases after using asymmetric A unit PT, compared to either an asymmetric FBT unit or the original BT unit. So, PPT has a more planar backbone conformation, stronger intermolecular contacts and higher degree of structural order than PBT and PFT, and also possesses a deeper HOMO level. When blended with PC61BM, a fullerene acceptor, the PPT-based device showed a power conversion efficiency (PCE) of 7.3%, which is higher than that of PFT- (6.7%) and PBT-based (6.2%) devices; when blended with ITIC, a non-fullerene acceptor, the PPT-based device showed a PCE of 5.4%, which is also higher than that of the PFT (4.4%) and PBT-based (4.7%) device. Most importantly, we discover that these blends consisting of either PC61BM or ITIC as the electron acceptor exhibit an average transmission of ∼60% over the 400 to 600 nm range and a maximum transmission of ∼70% at ∼500 nm, which provides opportunities and possibilities of achieving high performance, stable and visibly transparent PVs in the future.
Co-reporter:Jianyu Yuan, Michael J. Ford, Wanli Ma and Guillermo C. Bazan
Journal of Materials Chemistry A 2017 - vol. 5(Issue 19) pp:NaN8908-8908
Publication Date(Web):2017/04/18
DOI:10.1039/C7TA02510F
In comparison with many reported high-efficiency polymer solar cells, only 0.5% (v/v) additive is necessary to optimize a polymer/fullerene (PSFSiF/PC71BM) system, and the power conversion efficiency (PCE) was boosted from 2.4% to 8.0%. 2D grazing incidence wide angle X-ray scattering (GIWAXS) is utilized to understand the relevant structural features in the blend films prepared under different processing conditions, and the BHJ morphology is also examined using atomic force microscopy (AFM) and transmission electron microscopy (TEM) techniques.
Co-reporter:Victor Bochuan Wang, Jenny Du, Xiaofen Chen, Alexander W. Thomas, Nathan D. Kirchhofer, Logan E. Garner, Myat Thiri Maw, Wee Han Poh, Jamie Hinks, Stefan Wuertz, Staffan Kjelleberg, Qichun Zhang, Joachim Say Chye Loo and Guillermo C. Bazan
Physical Chemistry Chemical Physics 2013 - vol. 15(Issue 16) pp:NaN5872-5872
Publication Date(Web):2013/02/19
DOI:10.1039/C3CP50437A
It is important to tailor biotic–abiotic interfaces in order to maximize the utility of bioelectronic devices such as microbial fuel cells (MFCs), electrochemical sensors and bioelectrosynthetic systems. The efficiency of electron-equivalent extraction (or injection) across such biotic–abiotic interfaces is dependent on the choice of the microbe and the conductive electrode material. In this contribution, we show that spontaneous intercalation of a conjugated oligoelectrolyte, namely 4,4′-bis(4′-(N,N-bis(6′′-(N,N,N-trimethylammonium)hexyl)amino)-styryl)stilbene tetraiodide (DSSN+), into the membranes of Escherichia coli leads to an increase in current generation in MFCs containing carbon-based electrodes. A combination of scanning electron microscopy (SEM) and confocal microscopy was employed to confirm the incorporation of DSSN+ into the cell membrane and biofilm formation atop carbon felt electrodes. Current collection was enhanced by more than 300% with addition of this conjugated oligoelectrolyte. The effect of DSSN+ concentration on electrical output was also investigated. Higher concentrations, up to 25 μM, lead to an overall increase in the number of charge equivalents transferred to the charge-collecting electrode, providing evidence in support of the central role of the synthetic system in improving device performance.
Co-reporter:Nathan D. Kirchhofer, Xiaofen Chen, Enrico Marsili, James J. Sumner, Frederick W. Dahlquist and Guillermo C. Bazan
Physical Chemistry Chemical Physics 2014 - vol. 16(Issue 38) pp:NaN20443-20443
Publication Date(Web):2014/07/25
DOI:10.1039/C4CP03197K
Shewanella oneidensis MR-1 was cultivated on lactate with poised graphite electrode acceptors (E = +0.2 V vs. Ag/AgCl) in order to explore the basis for sustained increases in anodic current output following the addition of the lipid-intercalating conjugated oligoelectrolyte (COE), 4,4′-bis(4′-(N,N-bis(6′′-(N,N,N-trimethylammonium)hexyl)amino)-styryl)stilbene tetraiodide (DSSN+). Microbial cultures, which were spiked with DSSN+, exhibit a ∼2.2-fold increase in charge collected, a ∼3.1-fold increase in electrode colonization by S. oneidensis, and a ∼1.7-fold increase in coulombic efficiency from 51 ± 10% to an exceptional 84 ± 7% without obvious toxicity effects. Direct microbial biofilm voltammetry reveals that DSSN+ rapidly and sustainably increases cytochrome-based direct electron transfer and subsequently increases flavin-based mediated electron transfer. Control experiments indicate that DSSN+ does not contribute to the current in the absence of bacteria.
Co-reporter:Chao He, Chengmei Zhong, Hongbin Wu, Renqiang Yang, Wei Yang, Fei Huang, Guillermo C. Bazan and Yong Cao
Journal of Materials Chemistry A 2010 - vol. 20(Issue 13) pp:NaN2622-2622
Publication Date(Web):2010/02/09
DOI:10.1039/B921775D
It has been previously shown that incorporating alcohol/water-soluble conjugated polyelectrolytes (CPEs) as cathode interlayers can substantially enhance the open-circuit voltage (Voc) of bulk heterojunction polymer solar cells (PSCs). This improvement is attractive since there are only a few solution-based processing technologies that can enhance the Voc. In this article, the Voc enhancement effect of five distinct CPE materials was studied on three typical PSC device configurations, each using different donor materials. Significant Voc enhancement was observed in devices that contain a polyfluorene copolymer as the donor material. The origin of the Voc enhancement was investigated by examination of the dark currents.
Co-reporter:Gregory C. Welch, Louis A. Perez, Corey V. Hoven, Yuan Zhang, Xuan-Dung Dang, Alexander Sharenko, Michael F. Toney, Edward J. Kramer, Thuc-Quyen Nguyen and Guillermo C. Bazan
Journal of Materials Chemistry A 2011 - vol. 21(Issue 34) pp:NaN12709-12709
Publication Date(Web):2011/07/22
DOI:10.1039/C1JM11963J
We report on the design, synthesis and characterization of light harvesting small molecules for use in solution-processed small molecule bulk heterojunction (SM-BHJ) solar cell devices. These molecular materials are based upon an acceptor/donor/acceptor (A/D/A) core with donor endcapping units. Utilization of a dithieno(3,2-b;2′,3′-d)silole (DTS) donor and pyridal[2,1,3]thiadiazole (PT) acceptor leads to strong charge transfer characteristics, resulting in broad optical absorption spectra extending well beyond 700 nm. SM-BHJ solar cell devices fabricated with the specific example 5,5′-bis{7-(4-(5-hexylthiophen-2-yl)thiophen-2-yl)-[1,2,5]thiadiazolo[3,4-c]pyridine}-3,3′-di-2-ethylhexylsilylene-2,2′-bithiophene (6) as the donor and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) as the acceptor component showed short circuit currents above −10 mA cm−2 and power conversion efficiencies (PCEs) over 3%. Thermal processing is a critical factor in obtaining favorable active layer morphologies and high PCE values. A combination of UV-visible spectroscopy, conductive and photo-conductive atomic force microscopies, dynamic secondary mass ion spectrometry (DSIMS), and grazing incident wide angle X-ray scattering (GIWAXS) experiments were carried out to characterize how thermal treatment influences the active layer structure and organization.
Co-reporter:Zachary B. Henson, Peter Zalar, Xiaofen Chen, Gregory C. Welch, Thuc-Quyen Nguyen and Guillermo C. Bazan
Journal of Materials Chemistry A 2013 - vol. 1(Issue 37) pp:NaN11120-11120
Publication Date(Web):2013/07/19
DOI:10.1039/C3TA12690K
We present the design and synthesis of molecular organic semiconductors enabling processing from environmentally friendly solvents, including ethyl acetate. The structural changes employed do not adversely influence the attractive optical or electronic properties of the parent chromophore. Thin film transistors demonstrate the semiconducting ability of the new structures when processed from ethyl acetate.
Co-reporter:Chelsea Catania, Alexander W. Thomas and Guillermo C. Bazan
Chemical Science (2010-Present) 2016 - vol. 7(Issue 3) pp:NaN2029-2029
Publication Date(Web):2015/12/03
DOI:10.1039/C5SC03046C
Cationic conjugated oligoelectrolytes (COEs) varying in length and structural features are compared with respect to their association with E. coli and their effect on cell surface charge as determined by zeta potential measurements. Regardless of structural features, at high staining concentrations COEs with longer molecular dimensions associate less, but neutralize the negative surface charge of E. coli to a greater degree than shorter COEs.
Co-reporter:Wen Wen, Lei Ying, Ben B. Y. Hsu, Yuan Zhang, Thuc-Quyen Nguyen and Guillermo C. Bazan
Chemical Communications 2013 - vol. 49(Issue 65) pp:NaN7194-7194
Publication Date(Web):2013/05/28
DOI:10.1039/C3CC43229G
Regioregular conjugated polymers containing alternating pyridyl[2,1,3]thiadiazole (PT) and indacenodithiophene (IDT) structural units were synthesized. In these copolymers, the pyridyl nitrogen atoms on PT are precisely arranged along the backbone so that each one has an adjacent proximal and an adjacent distal counterpart across the two IDT flanking units. We find that despite the absence of obvious differences in orbital energy levels and optical bandgap, the regioregular materials exhibit larger charge carrier mobilities, as determined by using field effect transistor devices, and can yield higher solar cell power conversion efficiencies when mixed with fullerenes in bulk heterojunction active layers.
Co-reporter:Cheng-Kang Mai, Tomoya Arai, Xiaofeng Liu, Stephanie L. Fronk, Gregory M. Su, Rachel A. Segalman, Michael L. Chabinyc and Guillermo C. Bazan
Chemical Communications 2015 - vol. 51(Issue 99) pp:NaN17610-17610
Publication Date(Web):2015/09/28
DOI:10.1039/C5CC06690E
We report the synthesis of a series of water-soluble anionic narrow band-gap conjugated polyelectrolytes with a varied density of the ionic functional groups. The charge density is modulated by incorporating the structural units with tetraethylene glycol (TEG) monomethyl ether side chains. These polymers are readily p-doped during dialysis in water. CPEs with TEG side chains exhibit tighter intermolecular packing in the solid state and higher electrical conductivity.
Co-reporter:Jenny Du, Alexander W. Thomas, Xiaofen Chen, Logan E. Garner, Carol A. Vandenberg and Guillermo C. Bazan
Chemical Communications 2013 - vol. 49(Issue 83) pp:NaN9626-9626
Publication Date(Web):2013/09/02
DOI:10.1039/C3CC45094E
Variation in conjugated oligoelectrolyte (COE) repeat units is shown to affect the rate of COE insertion into mammalian membrane patches and membrane patch stabilities. These findings suggest that it is possible to find COE structures that do not destroy membranes while at the same time allow for more facile transmembrane movement of ions/substrates.
Co-reporter:Vinay Gupta, Lai Fan Lai, Ram Datt, Suresh Chand, Alan J. Heeger, Guillermo C. Bazan and Surya Prakash Singh
Chemical Communications 2016 - vol. 52(Issue 55) pp:NaN8599-8599
Publication Date(Web):2016/06/07
DOI:10.1039/C6CC03998G
A molecular donor of intermediate dimensions based on dithienogermole (DTG) as the central electron rich unit, coded as DTG(FBT2Th2)2, was designed and synthesized for use in bulk heterojunction, solution-processed organic solar cells. Under optimized conditions, a maximum power conversion efficiency (PCE) of 9.1% can be achieved with [6,6]-phenyl C71-butyric acid methyl ester (PC71BM) as the acceptor semiconductor component.
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