Thermodynamic Aspects of Excited State Electron Transfer Reactions

Thermodynamic Aspects of Excited State Electron Transfer Reactions 

The treatment of excited species as new chemical entities, and hence, the use of thermodynamics in dealing with their redox reactions is justified because in the condensed phase, the electronic relaxation times are usually several orders of magnitude longer than the time for thermal equilibration in all other degrees of freedom of a polyatomic molecule49, 50). 

The thermodynamics of excited states has been thoroughly discussed by Grabowski50, sl) with particular reference to acid-base equilibria (Forster s cycleS2 ). We will only consider here the problem of evaluating the difference between the redox potentials of M+/M and M+/ M (or M/M and M/M ) couples where M is the ground state molecule and M is an electronically excited state. 

A similar line of reasoning can be adopted to discuss excited state reduction. 

The difference in the free energy changes of reactions (8) and (9) can be expressed as follows 

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