Modulation of Excited State Proton Transfer Dynamics of a Lactim-Lactam Tautomeric System in Different Block Copolymer-Surfactant Aggregates.

The proton transfer (PT) process in 1-(2-hydroxy-5-chloro-phenyl)-3,5-dioxo-1H-imidazo-[3,4-b]isoindole (ADCL) has been studied in three different copolymer-surfactant supramolecular assemblies prepared in aqueous 1% P123 triblock copolymer micellar solution with varying concentrations of surfactants (sodium dodecyl sulfate (SDS), cetyltrimethylammonium bromide (CTAB), and triton-X-100 (TX 100)). The aim of the present study is to monitor the modulation of the PT process by changing the degree of micellar hydration inside the P123 micelle with the addition of the three different surfactants (two ionic and one non ionic), that is, in P123-surfactant aggregates. Besides, a comparative study has been done with these results with those in water, pure P123 micellar medium and three different surfactants medium. The micropolarity measurement and time-resolved fluorescence anisotropic measurements have been performed to evaluate the binding location of the probe (ADCL) in the three different copolymer-surfactant supramolecular assemblies. It is found that the micropolarity at the binding site of the molecule in the various environments largely influences the PT rate of ADCL. The PT rate is found to be the slowest in the P123 medium and in P123-surfactant aggregates the rate becomes faster as the micropolarity around the binding locations of the molecule in these aggregates is higher in comparison to that in P123 micelle.