Kinetics of Bimolecular Photophysical Processes

In the absence of photochemical reactions an excited-state molecule M can be deactivated by emission, by radiationless decay, or by quenching  

the ratio 4 p/ of the quantum yield of fluorescence without quencher to that with quencher is given by 

Because the direct measurement of lifetimes is easily performed nowadays, it is also useful to transform the Stern-Volmer relation into the form 

For many systems A is of the order 10 L mol s, that is, close to the diffusion-controlled rate constant Ana- This suggests that in these cases quenching is so rapid that the rate-determining step is the actual diffusion of the molecules to form an encounter complex. Thus, 

then A,(obs) = Ajj and the observed quenching rate that is equal to the diffusion rate will be dependent on solvent viscosity. 

the ratio of the quantum yield of fluorescence without 

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