ELECTRON-TRANSFER PHOTOSENSITIZED BY A TIN LIPOPORPHYRIN IN SOLUTION,MICELLES, AND AT WATER-ORGANIC SOLVENT INTERFACES

Electron transfer photosensitized by a tin lipoporphyrin [Sn(IV) etrak is-(((eicosanyloxy)carbonyl)phenyl)-porphyrin (SnLipoP)] is investigat ed under various solution conditions using a donor-SnLipoP-methylviolo gen (MV2+) ternary system, where the donor is triethanolamine (TEA) or ethylenediaminetetraacetic acid (EDTA). The photoreaction of SnLipoP is compared with the photoreactions sensitized by common Sn porphyrins like tin protoporphyrin IX (SnPP) and octaethylporphyrin (SnOEP). A c onstant photoreaction rate is observed in a water/organic solvent (hex ane, benzene) two-phase system in which the porphyrin (SnLipoP, SnOEP) is in the organic solvent and MV2+ is in the aqueous phase. The rate is monitored by the change in thr UV-visible absorption spectra produc ed by aqueous methylviologen radical MV2+. In contrast with the two-ph ase system, macroscopically us solutions (aqueous SnPP and micellar so lutions of SnLipoP, SnPP and SnOEP) give pseudo-logarithmic rates. The se electron-transfer processes are completely consistent with reductiv e primary electron transfer to the tin porphyrin and optical shielding effects. Differences in the rates for SnLipoP and the other Sn porphy rins are explained by structural differences in the porphyrins. In par ticular, the structure of the porphyrin influences the phase in which the porphyrin resides, its location relative to interfacial regions, a nd the way it interacts with itself and other system components. (C) 1 998 Elsevier Science S.A.