Self-assembly of a fluorescent galunamide derivative and sensing of acid vapor and mechanical force stimuli

Abstract

A galunamide derivative consisting of a fluorophore with benzoxazole and a cyano unit was designed and synthesized to realize a dual response to acid vapor and mechanical force. Photophysical properties and self-assembly were investigated. The dilute solution could respond to the acid stimulus, and the emission peak at 472 nm shifted to 535 nm with the addition of trifluoroacetic acid (TFA). Moreover, the derivative could self-assemble into thin nanofibers in its gel phase, and the fluorescence of the xerogel film is sensitive to TFA vapor. The emission color gradually changed from yellow to orange red upon exposure to acid vapor, and the detection limit is as low as 70 ppb for TFA. The solid exhibited a reversible fluorescence color change under the stimuli of mechanical force and solvent annealing. The UV-vis absorption and IR spectra indicate that the fluorescence color conversion can be attributed to the destruction of intermolecular hydrogen bonds and pristine π–π interaction induced by mechanical force.