Photoinduced electron transfer, catalysis

A biomimetic artificial photylase model was described by Wiest et al. [18] The model recognised pyrimidine dimers in both organic solvents and water. Excitation of the complex with visible light led to cycloreversion of the pyrimidine dimer through photoinduced electron-transfer catalysis (Scheme 21). 

Kosynkin, D., T. M. Bockman, and J. K. Kochi. Thermal (iodide) and photoinduced electron-transfer catalysis in biaryl synthesis via aromatic arylations with diazonium salts. J. Am. Chem. Soc. 119, 1997 4846-4855. 

Catalysis of Photoinduced Electron Transfer Reactions (Fukuzumi and... 

Preparation of photo-active and redox-active dendritic macromolecules, which undergo simultaneous muitielectron transfer is also attractive. Considering the potential applications of these multimetallic dendrimers as electron transfer mediators in redox catalysis, photoinduced electron transfer, and molecular electronics, new interesting results can be awaited in the near future. 

II. Fundamental concepts of catalysis on photoinduced electron transfer 110... 

V. Catalysis of metal ions on photoinduced electron transfer 143... 

Despite these apparent difficulties, there are now a number of examples for photoinduced electron transfer reactions that are significantly catalyzed. It is the purpose of this chapter to present fundamental concepts and the application of catalysis of photoinduced electron transfer reactions. The photochemical redox reactions, which would otherwise be unlikely to occur, are made possible to proceed efficiently by the catalysis on the photoinduced electron transfer steps. First, the fundamental concepts of catalysis on photoinduced electron transfer are presented. Subsequently, the mechanistic viability is described by showing a number of examples of photochemical reactions that involve catalyzed electron transfer processes as the ratedetermining steps. 

II. FUNDAMENTAL CONCEPTS OF CATALYSIS ON PHOTOINDUCED ELECTRON TRANSFER... 

If a third component (M), which can specifically stabilize one of the products of electron transfer, is introduced into the D -A system, the free energy change of photoinduced electron transfer is shifted to the negative direction, when the activation barrier of electron transfer is reduced to accelerate the rates of electron transfer, as shown in Figure 3, where M forms a complex with A ". It should be emphasized that there is no need to have an interaction of M with A and that the interaction with the reduced state (A ") is sufficient to accelerate the rate of photoinduced electron transfer. This contrasts sharply with the catalysis on conventional ionic or concerted reactions, in which the catalyst interacts with a reactant to accelerate the reactions. The initial interaction between M and A in the complex A-M, where charge is partially transferred from A to M, would also result in acceleration of the photoinduced electron transfer, since the reduction potential of A-M is shifted to the negative direction as compared to that of A. 

As shown above, the acid catalysis on electron transfer increases the overall efficiency of the photochemical reactions via photoinduced electron transfer without affecting the products. However, there are some cases when addition of an acid to a particular photoinduced electron transfer process results in... 

CATALYSIS OF METAL IONS ON PHOTOINDUCED ELECTRON TRANSFER 143... 

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