Dual probe solubilisation in two distinct regions of pure and mixed micelles: a pico-second time resolved fluorescence study

Photophysical parameters of a newly synthesised fluorescence probe, 2-[3-(N-methyl-N-phenyl amino)-2-propenylidene] indanone, have been studied in three different micellar media formed by the surfactants sodium dodecyl sulphate (SDS), cetyl trimethyl ammonium bromide (CTAB) and triton X-100 (TX100) and their binary mixtures (SDS–TX100, CTAB–TX100). Our study indicates that the probe molecules are distributed between the core and Stern/palisade layer of the micelle. The extent of distribution depends on the nature of the micelle. The radiative decay constant (kr) for the excited S1 state has been found to be independent of the nature of micellar media. However, the non-radiative decay constant (knr) exhibits significant medium dependence in the order SDS > CTAB ≈ TX100. Non-linear variation of knr with component surfactant composition in the mixed micelle has been observed and has been explained in terms of synergistic interaction between the surfactant molecules.