Carbazole modified salicylaldimines and their difluoroboron complexes: effect of the tert-butyl and trifluoromethyl terminal groups on organogelation and piezofluorochromism

New carbazole modified salicylaldimine derivatives 1a-3a and their difluoroboron complexes 1b-3b were synthesized. It was found that 3a and 3b bearing both tert-butyl and trifluoromethyl could form stable gels in some organic solvents, while no gel could be formed from 1a-1b and 2a-2b without tertbutyl or trifluoromethyl, respectively. It suggested that both tert-butyl and trifluoromethyl played key roles in the gel formation because they could tune the solubility of the compounds and adjust the strength of intermolecular interactions. It should be noted that there is no traditional gelation moiety involved in gelators 3a and 3b. The main driving force for the gelation of such nontraditional pi-gelators was pi-pi interaction. Meanwhile, aggregation-induced emission (AIE) was detected during the organogelation process of 3a, and the gel-sol transition took place upon adding F-. Interestingly, complexes 1b and 3b exhibited reversible piezofluorochromic (PFC) behaviors upon grinding/fuming, which originated from the transformation between crystalline and amorphous states. Herein, we provided a new strategy for designing new stimuli-responsive multifunctional soft materials.