Multi-stimuli responsive carbazole-imidazole derivatives: Effect of phenyl substitution and UV light-oxygen induced photochemical transformation

New carbazole-imidazole derivatives, (3-(4,5-diphenyl-1H-imidazole-2-yl)-9-(3-methoxyphenyl)-9H-carbazole (Cz-DPIM)) and 9-(3-methoxyphenyl)-3-(1,4,5-triphenyl-1H-imidazole-2-yl)-9H-carbazole (Cz-TPIM) are synthesized and investigated the effect of phenyl substitution on the fluorescence and stimuli-induced fluorescence properties. Cz-DPIM exhibited relatively strong fluorescence in solution compared to Cz-TPIM (Quantum yield (phi f, compared to quinine sulphate standard) = 0.28 (Cz-DPIM) and 0.09 (Cz-TPIM)). In contrast, Cz-DPIM is weakly fluorescence in solid-state but Cz-TPIM showed strong fluorescence (phi f = 1.3% (Cz-DPIM) and 18.2% (Cz-TPIM)). Cz-TPIM displayed mechanoresponsive reversible fluorescence switching upon crushing and solvent fuming. Both Cz-DPIM and Cz-TPIM exhibited reversible halofluorochromsim upon exposure of trifluoroacetic acid (TFA) and ammonia (NH3). Interestingly, Cz-DPIM and Cz-TPIM exhibited photocleavage upon UV light irradiation in presence of oxygen in CH3CN and produced green emissive fluorescence product. The controlled studies revealed that the presence of oxygen is important for exhibiting photocleavage by UV light exposure and suggest potential use for oxygen sensing application. The UV light and oxygen induced photocleavage of CzDPIM and Cz-TPIM also demonstrated in thin films.

Automated summary

New carbazole-imidazole derivatives, Cz-DPIM and Cz-TPIM, were synthesized and investigated for their fluorescence and stimuli-induced fluorescence properties. It was found that Cz-DPIM exhibited strong fluorescence in solution, while Cz-TPIM showed strong fluorescence in solid-state. Additionally, both Cz-DPIM and Cz-TPIM demonstrated photocleavage and emission of fluorescence products under specific conditions.