EXCIMER EMISSION OF PYRENE DERIVATIVES INDUCED BY IONIC DETERGENTS BELOW THE CRITICAL MICELLE CONCENTRATION

The fluorescence of three ionic pyrene derivatives in the presence of CTAC and SDS was investigated at detergent concentrations below the cr itical micelle concentration (CMC). The characteristic excimer emissio n was observed for surfactant concentrations more than one order of ma gnitude lower than the CMC. Lifetime measurements show that excimer fo rmation must be via a static mechanism. This is explained by the forma tion of mixed premicellar aggregates between the surfactants and the p robes. The quenching of the excimer emission by ionic (Tl+, S2O32-) an d neutral (N,N-dimethylaniline, fumaronitrile) species was studied. Th e quenching is only effective when the ions are of opposite charge to that of the detergent. The quenching by neutral species can be explain ed by a static mechanism which involves the association of the quenche r with the aggregates.