Excited-state intramolecular proton transfer of 2-(2'-hydroxyphenyl)benzimidazole in micelles

Abstract

Excited-state intramolecular proton transfer (ESIPT) of 2-(2'-hydroxyphenyl)benzimidazole (HPBI) has been studied using steady-state and time-resolved emission spectroscopy in neutral (Triton X-100), anionic (sodium dodecyl sulfate, SDS) and cationic (cetyltrimethylammonium bromide, CTAB) micelles. It is found that the tautomer intensity and the lifetime of the tautomer emission are sensitive monitors to estimate the critical micellar concentration (cmc) for all three micelles. Above the cmc the intensity of the normal emission band decreases while there is a large enhancement of the intensity of the tautomer emission along with a red shift of the emission maxima by about 20 nm. The decay of the normal emission of HPBI remains similar below and above the cmc for all three micelles. However, the lifetime of tautomer emission of HPBI increases sharply above the cmc. The enhanced tautomer emission is ascribed to the HPBI molecules residing in the less polar and aprotic interior of the micelles.