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 excipl exes formed between N,N-dimethylaniline (DMA) and several fluorescent probes containing the pyrene chromophore were studied in reversed mice llar 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 AO T 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. T he fluorescence of the MP-DMA exciplex is quenched with respect to pur e benzene by both reversed micellar systems. When the water content of the solution increases, the fluorescence quantum yield decreases in A OT, 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 q uenched by the surfactant. Triplet quantum yields and radical ion quan tum yields were determined by laser flash photolysis. In AOT solution radical ions are only present when the exciplex is formed in the inter face. In BHDC solutions radical ions are observed in all cases. The yi eld increases with the surfactant concentration and the water content. The results are interpreted as a consequence of the formation of clus ters under percolation conditions which may favor the charge separatio n in the geminate radical ion pair.