Three multi-responsiveness supramolecular metal-organic gels (MOGs) have been prepared upon Ba(OAc)₂, CdSO₄·8H₂O and Pb(NO₃)₂ with a simple ligand (G17) based on a carboxyl-functionalized benzimidazole derivative in alcoholic-water solutions. The MOGs display the formation of well-developed nanofibrillar networks composed of intertwined fibers which provide stability to gels structures through coordination, hydrogen bonding and π- π interactions characterized by using field emission scanning electron microscopy (FESEM), the fourier transform infrared (FT-IR) spectroscopy and powder X-ray diffraction (XRD) techniques. MOG-1 shows good stimuli responsiveness toward the changes in K₂CrO₄, both MOG-2 and MOG-3 do good job toward the changes in Na₂S. Moreover, because these MOGs were formed easily by gelator with some heavy metal ion, such as Cd(II) and Pb(II), it might provide the basis for heavy metal ion capture and removal.

A long wavelength emission fluorescent (612 nm) chemosensor with high selectivity for H₂PO₄⁻ ions was designed and synthesized according to the excited state intramolecular proton transfer (ESIPT). The sensor can exist in two tautomeric forms ('keto' and 'enol') in the presence of Fe³⁺ ion, Fe³⁺ may bind with the 'keto' form of the sensor. Furthermore, the in situ generated GY-Fe³⁺ ensemble could recover the quenched fluorescence upon the addition of H₂PO₄⁻ anion resulting in an off-on-type sensing with a detection limit of micromolar range in the same medium, and other anions, including F⁻, Cl⁻, Br⁻, I⁻, AcO⁻, HSO₄⁻, ClO₄⁻ and CN⁻ had nearly no influence on the probing behavior. The test strips based on 2-[2-hydroxy-4-(diethylamino) phenyl]-1H-imidazo[4,5-b]phenazine and Fe³⁺ metal complex (GY-Fe³⁺) were fabricated, which could act as convenient and efficient H₂PO₄⁻ test kits.

A facile approach to the design of stimuli-responsive supramolecular gels (SRSGs) termed double-metal-ion competitive coordination control is reported. By this means, the fluorescence signals and guest-selective responsiveness of the SRSGs are controlled by the competitive coordination of two different metal ions with the gelators and the target guest. To demonstrate this approach, a gelator G2 based on multiple self-assembly driving forces was synthesized. G2 could form Ca²⁺-coordinated metallogel CaG with strong aggregation-induced emission (AIE). Doping of CaG with Cu²⁺ results in AIE quenching of CaG and formation of Ca²⁺- and Cu²⁺-based metallogel CaCuG. CaCuG could fluorescently detect CN⁻ with specific selectivity through the competitive coordination of CN⁻ with the Cu²⁺ and the coordination of Ca²⁺ with G2 again. This approach may open up routes to novel stimuli-responsive supramolecular materials.

2,2′-Bisbenzimidazole derivative (L) was designed as a fluorescent chemosensor for Fe³⁺. This structurally simple chemosensor displays significant fluorescence quenching with increasing concentrations of Fe³⁺. L exhibited high selectivity and antidisturbance for Fe³⁺ among environmentally relevant metal ions in aqueous media. The method of Job's plot indicated the formation of 1:2 complex between L and Fe³⁺, and the possible binding mode of the system was also proposed. In addition, further study demonstrates the detection limit on fluorescence response of the sensor to Fe³⁺ is down to 10⁻⁷ mol·L⁻¹ range. The binding mode was investigated by fluorescence spectra, ESI-MS, IR data, ¹H NMR, ¹³C NMR and crystal data.

A novel copper selective sensor 2 based on hydrazide and salicylaldehyde has been designed and prepared. Sensor 2 behaves a single selectivity and sensitivity in the recognition for Cu²⁺ over other metal ions such as Fe³⁺, Hg²⁺, Ag⁺, Ca²⁺, Zn²⁺, Pb²⁺, Cd²⁺, Ni²⁺, Co²⁺, Cr³⁺ and Mg²⁺ in DMSO. The distinct color change and the rapid changement of fluorescence emission provide naked-eyes detection for Cu²⁺. The UV-vis data indicate that 1:2 stoichiometry complex is formed by sensor 2 and Cu²⁺. The association constant K_s was 3.51×10⁴ mol⁻¹·L. The detection limitation of Cu²⁺ with the sensor 2 was 2.2×10⁻⁷ mol·L⁻¹. The sensing of Cu²⁺ by this sensor was found to be reversible, with the Cu²⁺-induced color being lost upon addition of EDTA.