Dual emission of 2-(2'-hydroxyphenyl)-benzimidazole in reverse micelle

Abstract

Picosecond time resolved and steady state emission spectroscopy were employed 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 markedly affects the dual emission (normal and tautomer) of HPBI. While the normal emission is negligible in n-heptane, on addition of AOT and water its intensity increases gradually and reaches a moderate value (φ _f=0.04) at a water-to-surfactant ratio, w₀≈ 40. The decay of the normal emission becomes faster with addition of water. The intensity and lifetime of the tautomer emission increase on addition of AOT. The increase in the intensity of the normal emission with w₀ is ascribed to the formation of the polyhydrates in which excited state intramolecular proton transfer is blocked. The increase in the intensity of the tautomer emission in reverse micelles, compared with n-heptane, is attributed to the reduction in the non-radiative rates. The polarity of the water pool inferred from both the emission parameters of the normal, and the tautomer emission is less than that of ordinary bulk water.