Terthiophene derivatives of cholesterol-based molecular gels and their sensing applications

Three novel terthiophene derivatives of cholesterol (TtGC, TtLPC, TtDPC), of which the two building blocks are linked by a structure of glycine, l-phenylalanine, or d-phenylalanine, respectively, were designed and prepared, and their gelation behaviors in 26 liquids were tested. It was demonstrated that the compounds show different gelation abilities with the variation of the linker structures even though the variation is small. FTIR, (1)H NMR, and UV-vis measurements revealed that intermolecular hydrogen bonding and van der Waals interaction are the main driving forces for the gel formation. As for TtDPC, CD and AFM measurements revealed that it aggregated into chiral structures of left-helical feature in benzene. Importantly, the morphologies of the gel networks could be subtly adjusted via alteration of the gelator concentration. Considering the brightness in fluorescence and the unique micro/nanostructures of the gel networks, a fluorescent film (film 1) was fabricated by simple dip-coating of TtDPC/benzene solution (before gelation) onto a glass plate surface. Fluorescent studies demonstrated that the film is photochemically unstable. Two hours UV irradiation of the film results in film 2, which is almost fluorescent silence. However, the presence of HAc vapor or the vapors of some other volatile organic liquids induces new fluorescence emission, laying the foundation for creating a turn-on type fluorescent sensor of the organic vapors. Furthermore, as a new type of low-molecular-mass gelators (LMMGs), of which oligothiophene was employed as a building block, the present study has provided a possibility to explore the photo-/electronic applications of oligothiophenes via a molecular gel strategy.