EXCITED-STATE INTRAMOLECULAR PROTON-TRANSFER OF 2-(2'-HYDROXYPHENYL)BENZIMIDAZOLE IN MICELLES

Excited-state intramolecular proton transfer (ESIPT) of 2-(2'-hydroxyp henyl)benzimidazole (HPBI) has been studied using steady-state and tim e-resolved emission spectroscopy in neutral (Triton X-100), anionic (s odium dodecyl sulfate, SDS) and cationic (cetyltrimethylammonium bromi de, CTAB) micelles. It is found that the tautomer intensity and the li fetime of the tautomer emission are sensitive monitors to estimate the critical micellar concentration (cmc) for all three micelles. Above t he cmc the intensity of the normal emission band decreases while there is a large enhancement of the intensity of the tautomer emission alon g 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 f or all three micelles. However, the lifetime of tautomer emission of H PBI 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.