Photoinduced electron transfer supersensitization

Supersensitization of Photoinduced Electron Transfer in Monolayer Assemblies... 

Photoinduced electron-transfer reactions have also been observed in monolayer assemblies (23, 24). Such systems can be made essentially free of molecular diffusion and thus most closely resemble the solid state. They can be fabricated with precise geometry and therefore provide well-defined structures often lacking in amorphous solids or adsorbed layers. However, until now no evidence for enhancement of the yield of reaction (1) by added supersensitizers had been obtained, although the concept had been discussed (25). 

Penner, T. L. Moebius, D. Photoinduced electron-transfer processes in monolayer assemblies. Supersensitization in a three-component system. /. Am. Chem. Soc. 1982,104, 7407-7413. 

The photoinduced reduction of TCNQ by the porphyrin heterodimer ZnTPPS-ZnTMPyP provides a good illustration of these concepts [56,109]. Figure 12(a) displays photocurrent transients at the water DCE junction in the presence and absence of an equimolar ratio of Fe(CN)g /Fe(CN)g. The photocurrent relaxation in the absence of the aqueous redox couples is associated with the back electron transfer from TCNQ to the oxidized porphyrin complex. The substantial decrease in back electron transfer on addition of Fe(CN)g /Fe(CN)g is associated with the supersensitization phenomenon schematically depicted in Fig. 12(b). The back electron transfer from the radical TCNQ to the oxidized porphyrin complex is in competition with the regeneration of the dye by ferrocyanide. In the absence of back electron transfer, the overall reaction involves electron transfer from the redox species in the aqueous phase to TCNQ. In this case, the energetic balance is determined by the Galvani potential difference across the interface. 

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