Fluorescence-enhanced gels of D–π–A diphenylacrylonitrile derivatives: Influence of nitro group and alkoxy chain

• 4-Nitrodiphenylacrylonitrile compounds with methoxyl group and alkoxyl chain were synthesized.
• Some among them formed gel in organic solvent.
• One-dimensional nanofibers were observed in gels.
• Gelation induced enhanced emission.

4-nitrodiphenylacrylonitrile and diphenylacrylonitrile derivatives consisting of methoxy group and alkoxy chain with different lengths were synthesized and their gelation abilities were investigated. It was found that compounds with longer alkoxy chains and a nitro group could gelate some nonpolar and polar organic solvents. On the other hand, diphenylacrylonitrile derivatives without nitro group could not form gels in measured solvents, suggesting that the electron-withdrawing nitro moiety plays an important role in the gel formation. X-ray diffraction showed that gelator molecules stacked together with lamellar packing structures in the gel phases. More importantly, the gelators emitted very weak fluorescence in the solutions because of the twisted conformation in the isolated state. However, the gels had strong fluorescence owing to the suppression of molecular motion, molecular planarization and J-aggregate formation, implying gelation-induced emission enhancement.