ChemInform Abstract: Pressure Effects on the Fluorescence Decay of Pyrene in Micellar Solutions

Abstract

The monomer fluorescence decay of pyrene was measured in sodium dodecyl sulfate (SDS) and hexadecyltrimethylammonium chloride (HDTCl) micellar solutions as a function of pressure from 0.1 to 203 MPa at 25 /sup 0/C by a single-photon-counting technique. The decay curves were analyzed successfully by a conventional fluorescence decay analysis for micellar solution over the pressure ranges examined. From the analysis, it was found that the rate constant (k/sub E/) for intramicellar excimer formation decreased significantly with increasing pressure in both micellar solutions, while the cmc and the aggregation number (N) for SDS and HDTCl micelles were found to be almost independent of pressure. The activation volumes for excimer formation were 19 and 16 cm/sup 3//mol for SDS and HDTCl micellar solutions, respectively. An attempt to obtain an activation volume for a nonionic detergent was unsuccessful because of the failure of the decay profile to fit the theoretical model. However, activation volumes for microviscosity were obtained by studying the pressure dependence of intramolecular excimer formation of a dinaphthylpropane probe. The diffusion process in micelles and microviscosities are discussed by comparing the activation volume for excimer formation with those for microviscosities determined by the pressure effect on intrmolecular excimer formation, and bymore » comparing the results with those reported in the literature for a dipyrenylpropane probe.« less