Electron-Transfer Reactions in Micelles: Dynamics of Psoralen and Coumarin Radical Cations

Abstract

Radical cations of several psoralens and coumarins have been generated by photoionization in aqueous micellar solution for a comparison of their dynamic behavior with results observed previously in aqueous solution. The photoionization efficiencies are significantly higher in anionic sodium dodecyl sulfate (SDS) micelles than in aqueous solution as a result of favorable electrostatic effects that lead to rapid ejection of the electron into the aqueous phase. By contrast, much lower quantum yields are measured in neutral and cationic micelles. Experiments with anionic quenchers that are soluble only in the aqueous phase demonstrate that exit of the radical cations from anionic SDS micelles is too slow to measure (<105 s-1) under our conditions. Exit rate constants from neutral Triton X-100 micelles are approximately an order of magnitude faster. Comparison of equilibrium constants for both triplet and radical cations of 4,5‘,8-trimethylpsoralen demonstrates that electrostatic effects lead to an order of ma...