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 greater than or equal to 1 mM. In other solvents, e. g., water, it is only found in aggregate form, even at much lower concentra tions. Solvent polarity has a small and insignificant solvatochromic effect but alcohols give a specific interaction dth BDPEBB, causing a significant hypsachromic shift in absorption maxima and a large increase in relative f luorescence efficiency. Pyrene fluorescence is effectively quenched by BDPE BB. Pyrene also forms associative complexes with BDPEBB in water. These com plexes are partly dissociated in the presence of surfactant micelles. Trito n 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 dodecyl sulfate (SDS) and sodium decylsulfate (SDeS) micelles, inducing the formati on of large aggregates, visible by the naked eye. These targe aggregates ar e most probably microcrystals of BDPEBB2+/2DS(-) or BDPEBB2+/2DeS(-). The a ggregation number of SDS and SDeS micelles in the absence and in the presen ce of BDPEBB has been calculated by exploitation of the static luminescence quenching kinetics of Ru(bpy)(3)(2+) by 9-methylanthracene, both solubiliz ed 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 p articular care if they are to be used as probes of the micellar phase. (C) 2000 Academic Press.