Kinetic Aspects of Bimolecular Processes

Leaving aside for the moment a detailed treatment of the rate of photoinduced energy-and electron transfer (Sects. 2.3 and 2.5), wc will briefly recall here some fundamental kinetic aspects of bimolecular processes involving excited states. 

For processes requiring diifusion and formation of encounters, we can use the Stem-Volmer model which assumes statistical mixing of A and B. The simplest case is that of a species A that decays via some intramolecular paths and, in fluid solution, can encounter a quencher B. The excited state lifetimes in the absence (tq) and in the presence (t) of the quencher B are given by (2.8) and (2.9), where kg is the bimolecular constant of the quenching process. 

Dividing (2.8) by (2.9), yields the well-known Stern-Volmer Eq. 2.10 

The key step of the process is, of course, the unimolecular electron-(or energy-) transfer step (ke). Before going into more details (Sect. 2.2.3), it is important to extend our discussion to photoinduced energy and electron transfer processes in supramolecular systems where A does not need to diffuse to encounter B, but is already more or less close to B because A and B are linked together. 

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