Organogelation of cyanovinylcarbazole with terminal benzimidazole: AIE and response for gaseous acid

New cyanovinylcarbazole functionalized benzimidazoles CCBM and TCBM were synthesized. It was found that they could self-assemble into organogels in some mixed solvents rapidly upon stimulation by ultrasound. Although the emission of CCBM and TCBM in solutions was very weak, the xerogel-based films emitted intense yellow light under UV irradiation on account of AIE (aggregation-induced emission). It was further proved by the fact that the aggregates emitted strong yellow light in THF/water with high water fraction, while they were almost non-emissive in THF. We found that the emission of CCBM and TCBM in THF/water with high water fraction could be quenched by TFA (trifluoroacetic acid) significantly, so these hydrophobic dyes could be applied to detect acids in water phase. It should be noted that the emission of the nanofibers-based films of CCBM and TCBM could also be quenched rapidly upon exposed to TFA vapor. Particularly, the thinner the film, the higher the performance detected for the sensory properties. For example, the detection limit and the decay time of CCBM towards gaseous TFA in nanofibers-based film with the thickness of 0.21 μm were 0.33 ppm and 0.38 s, respectively, and those were 8.0 ppm and 2.5 s for the film with the thickness of 1.73 μm. We provided a strategy for fabricating new fluorescence sensory materials with high performance in probing gaseous acid via organogelation.