Excited state intramolecular proton transfer in 2-(2′-benzamidophenyl)benzimidazole: effect of solvents

Excited state intramolecular proton transfer (ESIPT) process in 2-(2′-benzamidophenyl)benzimidazole (2-BAPBI) has been studied in different solvents by means of absorption, fluorescence, fluorescence excitation and time resolved spectroscopy. Dual fluorescence (normal and tautomer emissions) is observed in all the solvents. The quantum yield of the tautomer emission is always larger than that of the normal emission. This is because of the enhanced rate of ESIPT process which arises due to the presence of the electron withdrawing benzoyl group as a substituent to one of the hydrogen atom of the amino group in 2-(2′-aminophenyl)benzimidazole (2-APBI).