Excited-state intramolecular proton transfer in the anionic species of 2-(2 '-acetamidophenyl) benzimidazole in aqueous medium

An excited-stare intramolecular proton transfer (ESIPT) process has been ob served in the anionic species of 2,-(2'-acetamidophenyl)benzimidazole (2-AM PBI). Dual fluorescence is observed in the case of monoanionic species. The presence of different monoanionic species has been characterized by means of steady-state and time-resolved fluorescene spectroscopy, as well as usin g AM1 semi-empirical quantum-mechanical calculations. The present study rev ealed that the presence of an acetyl group plays a vital role in the stabil ity of different ionic and neutral species and in changes in their ground ( S-0) and excited singlet state (S-1) acid-base properties with respect to 2 -(2'-aminophenyl)benzimidazole (2-APBI). (C) 2000 Elsevier Science B.V. All rights reserved.