Photophysical Behavior of a New Gemini Surfactant in Neat Solvents and in Micellar Environments

A novel fluorescent gemini surfactant, 1,4-bis-(2'-(N-dodecyl pyridinio-4"-yl)ethenyl)benzene dibromide, abbreviated BDPEBB, has been synthesized and its photophysical properties have been studied in different environments. BDPEBB has a limited solubility in alcohols where it is found in aggregate form at concentrations>/=1 mM. In other solvents, e.g., water, it is only found in aggregate form, even at much lower concentrations. Solvent polarity has a small and insignificant solvatochromic effect but alcohols give a specific interaction with BDPEBB, causing a significant hypsochromic shift in absorption maxima and a large increase in relative fluorescence efficiency. Pyrene fluorescence is effectively quenched by BDPEBB. Pyrene also forms associative complexes with BDPEBB in water. These complexes are partly dissociated in the presence of surfactant micelles. Triton X-100 micelles provide a favorable environment for BDPEBB solubilization well distinguished from the behavior of ionic surfactants. Small quantities of BDPEBB have a large influence on the behavior of aqueous sodium dodecylsulfate (SDS) and sodium decylsulfate (SDeS) micelles, inducing the formation of large aggregates, visible by the naked eye. These large aggregates are most probably microcrystals of BDPEBB(2+)/2DS(-) or BDPEBB(2+)/2DeS(-). The aggregation number of SDS and SDeS micelles in the absence and in the presence of BDPEBB has been calculated by exploitation of the static luminescence quenching kinetics of Ru(bpy)(3)(2+) by 9-methylanthracene, both solubilized in the micellar phase. It has been observed that Ru(bpy)(3)(2+) inhibits the precipitation of SDeS micelles in the presence of BDPEBB. Our results suggest that double-chain surfactant chromophores should be employed with particular care if they are to be used as probes of the micellar phase. Copyright 2000 Academic Press.