Electron transfer exergonic

Since the occurrence of the ECE mechanism implies that yD , B, it follows that Kd 1, meaning that the disproportionation reaction is strongly exergonic. Since we have assumed that the two electrode electron transfer reactions are fast, the same is true for the disproportionation... 

Electronic excitation of molecules lead to a drastic change of their reactivities. One effect of the excitation is the powerfiil change of the redox properties, a phenomenon which may lead to photoinduced electron transfer (PET) [1-4] The electron-donating as well as the electron-accepting behavior of the excited species are approximately enhanced by excitation energy. This can be explained by means of a simple orbital scheme. By excitation of either the electron donor (D) or the acceptor (A) of a given pair of molecules, the former thermodynamically unfavorable electron transfer process becomes exergonic (A et) (Scheme 1). 

In contrast to thermal electron-transfer processes, the back-electron transfer (BET) (kbet) in the PET is generally exergonic as well. The apparent contradiction can be resolved by the cyclic process excitation-electron transfer-back-electron transfer in which the excitation energy is consumed. The back-electron transfer is not the formal reverse reaction of the photoinduced-electron-transfer step and so not necessarily endergonic. This has different influences on PET reactions. On the one hand, BET is the reason for energy consumption and low quantum yields. On the other hand, it can cause more complex reaction mechanisms if the... 

An increase in the ion annihilation exergonicity AG to values comparable to the excited triplet-state energies (AG I LT < 0) opens an additional electron transfer channel (T-route). In the simplest case, only one excited triplet 3 A or 3 D becomes accessible. Triplet emission can be directly observed from the ECL systems involving rare earth and transition metal complexes with allowed (due to extensive spin-orbit coupling) triplet-singlet electronic transition. 

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