PICOSECOND LASER STUDIES ON THE DYNAMICS OF COMPACT ION-PAIRS - COMPARISON BETWEEN HOMOGENEOUS AND MICELLAR SOLUTION

The dynamics of compact ion pairs generated by photoexcitation of charge-transfer complexes between viologen and naphthalene derivatives have been studied by laser flash photolysis. Ion pair lifetimes and charge separation efficiencies have been measured, which allows us to determine directly charge recombination and free ion dissociation rate constants. The free energy of the charge recombination reaction has been calculated from the one-electron redox potentials of electron donor and acceptor that have been measured electrochemically. Plots of charge recombination rate constants vs the free energy show the "Marcus-inverted" region. Ion dissociation rate constants increase with decreasing complex stability constants which have been obtained from Benesi-Hildebrand plots. The results in homogeneous (acetonitrile and butyronitrile) and heterogeneous (SDS micellar solution) environments are compared, and micellar effects on the formation of charge-transfer complexes, on electron-transfer reactions, and on solvation processes are discussed.