KINETIC AND STATISTICAL FEATURES OF TRIPLET ENERGY-TRANSFER PROCESSES IN MICELLAR ASSEMBLIES

A kinetic model is presented describing the salient features of energy transfer processes in micellar assemblies. It takes into account specific effects resulting from the compartmentation of the reactants in the surfactant host aggregates. The time laws derived are used to analyze experimental data obtained from the laser photolysis studies where triplet N-methylphenothiazine (MPTHT) was used as a donor and trans-stilbene or naphthalene as an acceptor, respectively. Both were solubilized in aqueous micellar solutions of cetyltrimethylammonium bromide (CTAB). In the MPTHT-stilbene system the transfer is irreversible and occurs with a rate constant kq = 1.5 × 107 s-1 for micelles containing one donor-acceptor pair. Conversely, the reaction between MPTHT and naphthalene is reversible, the respective rate constants for the forward and backward transfer being kq = 2.8 × 106 s-1 and k-q = 3.3 × 106 s-1. Comparison with data obtained in homogeneous solution reveals that the confinement of the reaction space to micellar size induces both a drastic enhancement of the observed transfer rate as well as a reduction of the reaction order from two to one. From the experimental results it is also possible to obtain direct information on the statistical laws that govern the partitioning of the solubilizate molecules over the micelles. This was found to be the Poisson distribution function. © 1979 American Chemical Society.