PHOTOINDUCED ELECTRON-TRANSFER FROM EOSIN AND ETHYL EOSIN TO FE(CN)(6)(3-) IN AOT REVERSE MICELLES - SEPARATION OF REDOX PRODUCTS BY ELECTRON-TRANSFER-INDUCED HYDROPHOBICITY

The photoinduced electron transfer from eosin, Eo(2-) (1), and ethyl e osin, EoEt(-) (2), to Fe(CN)(6)(3-) is examined in AOT reverse micelle s in heptane. For a microheterogeneous system having a water-to-surfac tant molar ratio w = 30, the lifetime of the photogenerated redox prod ucts in the system that includes EoEt(-) is ca. 300-fold longer than i n the photosystem that includes Eo(2-): tau = 4.3 mu s for Eo(2-) and tau = 1400 mu s for EoEt(-). Stabilization of the redox products again st recombination in the system containing EoEt(-) is attributed to the extraction of the hydrophobic oxidized photoproduct (2)EoEt(.) from t he water pool of the reverse micelles to the continuous oil phase. Pho toinduced electron transfer from Eo(2-) to Fe(CN)(6)(3-) in the revers e micelles has been quantitatively analyzed by assuming a Poisson dist ribution of the quencher over the reverse micelles. Kinetic analysis o f the transients allowed determination of the quencher distribution, m icelle concentration [m] 1.44 x 10(-4) M, and water-pool diameter 2R = 82 Angstrom. The kinetics of photoinduced electron transfer from EoEt (-) to Fe(CN)(6)(3-) could be analyzed in terms of a similar quencher distribution. Detailed kinetic analysis revealed that, in the Eo(2-)/F e(CN)(6)(3-) reverse-micellar photosystem, photoinduced electron trans fer is followed by a fast intramicellar recombination. In the EoEt(-)/ Fe(CN)(6)(3-) photosystem, fast escape of the neutral oxidized species (2)EoEt(.) from the reverse micelle competes with the intramicellar r ecombination (escape efficiency: theta(esc) = 0.52), leading to separa tion of the redox products. The separated photoproducts undergo a slow secondary recombination. A kinetic model for the overall photochemica l processes is presented, and kinetic equations for the photoinduced e lectron transfer in the reverse micelles followed by intramicellar rec ombination and escape are provided.