Electron Transfer Reaction of the Excited State

Without entering into the details of the bimolecular quenching processes, it is necessary to know that the lowest excited state of a given complex, A, can act as an energy donor, an electron acceptor (oxidant) or an electron donor (reductant)  

Therefore, the oxidative quenching is a thermodynamically favourable reaction it is thus not surprising that this same reaction is very fast kg 10 M s in H2O at room temperature. One can also imagine that the back reaction (recombination) is even more favourable, either thermodynamically or kinetically  

Numerous examples of photoinduced electron transfer reactions can be found in the literature, making use of Ru(bipy)3 as photoactive component [6], the redox partner being an inorganic cation, a transition metal complex or an organic species. 

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Balzani, V., Bolletta, F., Gandolfi, M. T., and Maestri, M. Bimolecular Electron Transfer Reactions of the Excited States of Transition Metal Complexes. 75, 1-64 (1978). 

Bimolecular Electron Transfer Reactions of the Excited States of Transition Metal Complexes... 

Figure 1. Cartoon outlining the steps involved in converting solar energy (hv) to stored chemical energy or electricity. Electron transfer reactions of the excited state (denoted by an asterisk) with donors (D) or acceptors (A) to yield charge-separated species (D or A-) take place in competition with nonproductive emission (hv ), nonradiative excited-state decay, and hack electron transfer, which...

Charge separation Ion — pair fmmation by ionization of exciton, applied potential or reaction with impurities Electron transfer reaction of the excited state with acceptor or donor... 

Electron transfer reactions of the excited states of metal ion complexes continue to attract much attention with interest in solar energy storage and the cleavage of H2O to H2 and 02. ° " ° A useful review of the properties of excited-state polypyridine complexes has appeared. The much studied [ Ru(bipy)3] and related systems remain at the forefront of new work but other metal ion systems are attracting increasing interest (Table 1.3.) When a complex is photochemically activated to form ML, excited state... 

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