DUAL EMISSION OF 2-(2'-HYDROXYPHENYL)-BENZIMIDAZOLE IN REVERSE MICELLE

Picosecond time resolved and steady state emission spectroscopy were e mployed to study the dual emission phenomenon of 2-(2'-hydroxyphenyl)- benzimidazole (HPBI) in aerosol OT (AOT) reverse micelle in n-heptane. It is observed that the microenvironment inside the water pool marked ly affects the dual emission (normal and tautomer) of HPBI. While the normal emission is negligible in n-heptane, on addition of AOT and wat er its intensity increases gradually and reaches a moderate Value (phi (f) = 0.04) at a water-to-surfactant ratio, w(0) approximate to 40. Th e decay of the normal emission becomes faster with addition of water. The intensity and lifetime of the tautomer emission increase on additi on of AOT. The increase in the intensity of the normal emission with w (0) is ascribed to the formation of the polyhydrates in which excited state intramolecular proton transfer is blocked. The increase in the i ntensity of the tautomer emission in reverse micelles, compared with n -heptane, is attributed to the reduction in the non-radiative rates. T he polarity of the water pool inferred from both the emission paramete rs of the normal, and the tautomer emission is less than that of ordin ary bulk water. (C) 1997 Elsevier Science S.A.