DYNAMICS OF LIGHT-INDUCED REDOX PROCESSES IN MICROEMULSION SYSTEMS

Photoredox processes of the kind shown in eq 1 were investigated in oil/water microemulsions (water content > 80%) by means of laser photolysis and steady-state illumination techniques. The following two redox couples were employed: (1) A = duroquinone (DQ), D = diphenylamine (DPA), and (2) A = methylviologene (MV2+), D = N-methylphenothiazine (MPTH). In the first system, the two reactants are both solubilized in the lipid interior of the microemulsion droplet. The electron transfer from DPA to photoexcited DQ was found to occur in two steps: a rapid subnanosecond reaction involving DQ singlet states and a slower triplet reaction occurring in the microsecond time range. The diphenylamine cation produced associates with parent DPA molecules to yield multimer complexes. This process is controlled by the statistics of probe distribution among the droplets. A detailed account of the kinetics of formation and spectral characteristics of the multimers is given. In the second system, the electron transfer occurs from MPTH excited states inside the droplet to MV2+ which is absorbed on the droplets' surface. It exhibits also a fast (nanosecond) and a slower (microsecond) component resulting from the reaction of singlet and triplet states. The fate of the radical ions produced is examined and photobiological implications are discussed. © 1978, American Chemical Society. All rights reserved.