Temperature dependence of excimer formation and excimer fluorescence polarization in micellar dispersions: Surfactants as intrinsic probes

Experiments have been carried out in which the temperature dependence of the fluorescence spectrum of alkylbenzenesulfonate surfactants has been studied. Excitation of the benzene chromophore above the critical micelle concentration in aqueous dispersions showed the presence of the spectral components due to both monomer and excited dimer species. The ratio of the intensities of the two fluorescent peaks allowed an examination of the monomer-excimer equilibrium in the micellar phase. The activation energy of excimer formation for different isomers was obtained and comparisons drawn with the behavior of sterically hindered benzenes in homogeneous solution. In other studies, pyrene molecules were incorporated in the surfactant micelles as extrinsic probes. Temperature studies of its monomer-excimer behavior enabled both excimer binding energy and activation energy to be evaluated. It was concluded that the pyrene probe and the benzene intrinsic probe occupy the micellar assembly such that their environments exhibit different viscosities.