| Résumé | The photoreduction of butyrophenone by α-tocopherol in anionic micelles has been examined by laser flash photolysis. The reaction leads to a triplet-derived radical pair that decays by a competition of escape processes and geminate reactions. The dependence of both processes on the surfactant's chain length, the addition of electrolytes, and the temperature were examined in detail. The rate constants for radical exit from the micelles (k-) follow Arrhenius-type behavior; for example, the exit from sodium dodecyl sulfate micelles occurs with an activation energy of 6.5 kcal/mol and log (A/s-1) = 10.7. The results suggest that entropy plays an important role in determining the dynamics of escape processes. The rate constants for geminate reaction (kgem are largely determined by the size of the micelles. Both spin evolution and the frequency of reencounters are important in controlling geminate processes. For the radical pair examined, spin evolution is believed to be controlled by hyperfine couplings, while the frequency of reencounters depends upon micellar size and intramicellar diffusion dynamics. |
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