Electric field effects on photoexcitation dynamics and electronic properties of highly efficient indoline sensitizers, DN488, D205, and DN182, embedded in PMMA films have been examined by using electroabsorption (E-A) and electrophotoluminescence (E-PL) spectroscopic techniques and time-resolved photoluminescence (PL) decay measurements in the presence of electric fields. Photovoltaic performances have been also measured for devices constructed using these sensitizers. Then, field-induced quenching of PL and field-induced change in PL decay profile were observed, and it was found that these field effects, which depend on the sensitizers investigated herein, are well correlated with the trend of power conversion efficiencies of the corresponding photovoltaic cells. Electric dipole moment and molecular polarizability of these sensitizers both in the ground state (S0) and in the excited state have been calculated at the level of B3LYP/6-31G(d), and the differences of these physical parameters between S0 and the excited state thus obtained have been compared with the ones determined from the E-A and E-PL spectra. The present study of Stark spectroscopy of indoline dyes provides new insights for the exciton dissociation property and carrier mobility of organic dyes, which are important factors to understand the operation mechanism in dye-sensitized solar cells.

The thermodynamics and dynamics of a carbonaceous molecular bearing comprising a belt-persistent tubular molecule and a fullerene molecule have been investigated using density functional theory (DFT). Among ten representative methods, two DFT methods afforded an association energy that reasonably reproduced the experimental enthalpy of −12.5 kcal mol−1 at the unique curved π-interface. The dynamics of the molecular bearing, which was assembled solely with van der Waals interactions, exhibited small energy barriers with maximum values of 2–3 kcal mol−1 for the rolling motions. The dynamic motions responded sensitively to the steric environment and resulted in two distinct motions, precession and spin, which explained the unique NMR observations that were not clarified in previous experimental studies.

•Electroabsorption spectra of subphthalocyanines have been observed.•Electrophotoluminescence spectra of subphthalocyanines have been observed.•The excited states of subphthalocyanine are shown to have a charge transfer character.•Nonradiative process at the emitting state of subphthalocyanines is enhanced by electric fields.Electric field effects on the electronically excited states have been investigated for two subphthalocyanines, F-SubPc and T-SubPc, which have the electron-withdrawing and electron-donating substituents, respectively. In contrast with T-SubPc, the directions of the electric dipole moment in the excited states S1 and S2 of F-SubPc are found to be very different from that in the ground state S0. The S1 and S2 states of T-SubPc show a prominent charge-transfer character, suggesting that T-SubPc is a suitable candidate as the dye in photovoltaic cells. Electrophotoluminescence spectra suggest that the intersystem crossing from S1 to T1 is enhanced by electric fields.

There have been a growing number of articles that report dramatic improvements in the experimental performance of chemical reactions by microwave irradiation compared to that under conventional heating conditions. We theoretically examined whether nonthermal microwave effects on intramolecular reactions exist or not, in particular, on Newman–Kwart rearrangements and intramolecular Diels–Alder reactions. The reaction rates of the former calculated by the transition state theory, which consider only the thermal effects of microwaves, agree quantitatively with experimental data, and thus, the increases in reaction rates can be ascribed to dielectric heating of the solvent by microwaves. In contrast, for the latter, the temperature dependence of reaction rates can be explained qualitatively by thermal effects but the possibility of nonthermal effects still remains regardless of whether competitive processes are present or not. The effective intramolecular potential energy surface in the presence of a microwave field suggests that nonthermal effects arising from potential distortion are vanishingly small in intramolecular reactions. It is useful in the elucidation of the reaction mechanisms of microwave synthesis to apply the present theoretical approach with reference to the experiments where thermal and nonthermal effects are separated by screening microwave fields.

We investigated the reaction paths of Stone–Wales rearrangement (SWR), i.e., π/2 rotation of two carbon atoms with respect to the midpoint of the bond, in graphene and carbon nanotube quantum chemically. Our particular attention is focused on the roles of electronic excitations and conical intersections (CIs) in the reaction mechanism. We used pyrene as a model system. The reaction paths were determined by constructing potential energy surfaces at the MS-CASPT2//SA-CASSCF level of theory. We found that there are no CIs involved in SWR when both of C–C bond cleavage and formation occur simultaneously (concerted mechanism). In contrast, for the reaction path with stepwise cleavage and formation of C–C bonds, C–C bond breaking and making processes proceed through two CIs. When SWR starts from the ground (S0) state, the concerted and stepwise paths have an equivalent reaction barrier ΔE‡ (9.5–9.6 eV). For the reaction path starting from excited states, only the stepwise mechanism is energetically preferable. This path contains a nonadabatic transition between the S1 and S0 states via a CI associated with the first stage of C–C bond cleavage and has ΔE‡ as large as in the S0 paths. We confirmed that the main active molecular orbitals and electron configurations for the low-lying electronic states of larger nanocarbons are the same as those in pyrene. This result suggests the importance of the nonadiabatic transitions through CIs in the photochemical reactions in large nanocarbons.

Recently, molecular rotor systems have been emerging as a promising candidate of functional nanoscale devices. A macroscopic gyroscope like molecule in a crystalline solid is particularly unique owing to its variable physicochemical properties. Setaka et al. have achieved the synthesis of a novel crystalline molecular gyroscope characterized by a closed topology with a phenylene rotator encased in three long siloxaalkane spokes [Setaka, W.; et al. Chem. Lett.2007, 36, 1076]. We theoretically investigated the underlying mechanism of its rotational dynamics by utilizing the self-consistent-charge density-functional-based tight-binding (DFTB) method for crystal structures. We first found that the DFTB semiquantitatively reproduced the unit cell molecular geometries of all three stable X-ray structures under the periodic boundary condition. From the potential energy surface calculations, the activation barrier for phenylene rotation was estimated to be about 1.2 kcal/mol, which is much lower than those of other, previously synthesized gyroscopic compounds. In comparison to 1,4-bis(trimethylsilyl)benzene of a similar crystal structure but of an open topology, the siloxaalkane frame in the crystalline molecular gyroscope under consideration effectively blocks strong intermolecular steric interactions experienced by the phenylene rotator. The molecular dynamics simulations based on the DFTB exemplified facile phenylene flipping between the stable structures, especially at high temperature. The present results demonstrate the remarkable ability of the DFTB method to predict the crystal structures and rotational dynamics of this type of crystalline molecular gyroscopes.

The thermodynamics and dynamics of a carbonaceous molecular bearing comprising a belt-persistent tubular molecule and a fullerene molecule have been investigated using density functional theory (DFT). Among ten representative methods, two DFT methods afforded an association energy that reasonably reproduced the experimental enthalpy of −12.5 kcal mol−1 at the unique curved π-interface. The dynamics of the molecular bearing, which was assembled solely with van der Waals interactions, exhibited small energy barriers with maximum values of 2–3 kcal mol−1 for the rolling motions. The dynamic motions responded sensitively to the steric environment and resulted in two distinct motions, precession and spin, which explained the unique NMR observations that were not clarified in previous experimental studies.