Time-resolved studies of fluorescence quenching in a water-in-oil microemulsion

Abstract

Nanosecond time-resolved spectrofluorimetry has been used to study the kinetics of quenching of acridinium-ion fluorescence by Co²⁺ and Br^– ions in a water-in-oil microemulsion stabilised by AOT [sodium 1,4-bis(2-ethylhexyl)-sulphosuccinate]. Analysis of the fluorescence decay curves leads to the determination of the aggregation number of the water droplets and the second-order rate constants for quenching in the dispersed water phase, both as functions of the water-to-surfactant mole ratio, W₀. Quenching by both Br^– and Co²⁺ ions is impeded relative to the diffusion-controlled process in aqueous solutions of high ionic strength, but the rate constant for Co²⁺ quenching increases with W₀, whereas that for Br^– decreases. This behaviour can be explained in terms of the distribution of ions and the variation of microviscosity within the reverse micelle.