INTERFACE EFFECT ON THE PROPERTIES OF EXCIPLEXES FORMED BETWEEN PYRENE DERIVATIVES AND N,N-DIMETHYLANILINE IN REVERSED MICELLES

The fluorescence spectra and fluorescence quantum yields of the exciplexes formed between N,N-dimethylaniline (DMA) and several fluorescent probes containing the pyrene chromophore were studied in reversed micellar solutions. The solutions were made from sodium bis(2-ethylhexyl) sulfosuccinate (AOT) or benzylhexadecyldimethylammonium chloride (BHDC), water, and benzene. The probes used were 1-methylpyrene (MP) in AOT and BHDC, [4-(1-pyrenyl)butyl]trimethylammonium bromide (PBTMA) in AOT and pyrenebutyric acid (PBA) in BHDC. The fluorescent quantum yields and lifetimes of the exciplexes were determined as a function of the surfactant concentration and the water content of the microemulsion. The fluorescence of the MP-DMA exciplex is quenched with respect to pure benzene by both reversed micellar systems. When the water content of the solution increases, the fluorescence quantum yield decreases in AOT, while it increases in BHDC. For the probes bound to the micelle's interface the emission maximum is red-shifted with respect to benzene. In BHDC solutions the fluorescence of the exciplexes is drastically quenched by the surfactant. Triplet quantum yields and radical ion quantum yields were determined by laser flash photolysis. In AOT solution radical ions are only present when the exciplex is formed in the interface. In BHDC solutions radical ions are observed in all cases. The yield increases with the surfactant concentration and the water content. The results are interpreted as a consequence of the formation of clusters under percolation conditions which may favor the charge separation in the geminate radical ion pair.