Electron-Transfer Reactions in Organic Systems

Intermolecular electron-transfer reactions in organic systems 

The sequence of events after photoexcitation of such a donor-acceptor molecule DA may be represented (in the simplest case) as  

Here step 1 is the initial light-absorption, commonly by the donor moiety in step 2 the excitation energy is quickly distributed among the bonds of the molecule. Electron transfer (step 3) gives rise to the contact ion-pair D A this is called a charge-separation (CS) 

Geminate recombination is a special case, in as much as it is a bimolecular reaction but does not involve diifusion, since the reactants are already adjacent (Section 7.3.4.1). The rate constant therefore refers to a reaction between a donor and an acceptor at a fixed distance apart, close to the van der Waals contact distance. For the electron-transfer reaction R+CP — RCl (with R = CPh2Me), the rate constant has been determined as 3.81 X 10 s [22], The rate constants for charge separation and recombination can also be found, using the quantum yield (0) of radicals escaping from the geminate radical pair [0 — kcs/(kcs + cr)]. which can be determined by use of a cation radical trap such as dimethoxystilbene. 

An important contribution from the field of intramolecular organic electron-transfer is the discovery of some reactions that clearly show the inverted region indicated by the Marcus formalism [23]. As we noted earlier (Section 9.1.2.6), the Marcus model predicts that, in 

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Photosensitized Electron-Transfer Reactions in Organized Systems... 

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