Energy transfer rapid diffusion limit

Thomas, D.D., Carlsen, W.F., and Stryer, L. (1978) Fluorescence energy transfer in the rapid-diffusion limit. Proc. Natl. Acad. Sci. USA 75(12), 15746-15750. 

It is interesting to note that energy transfer in the rapid diffusion limit is sensitive to the distance of closest approach of the donor and acceptor. Based on this observation, some interesting applications in biology have been described, such as the measurement of the distance at which an acceptor is buried in biological macromolecules and membrane systems. 

Thomas D. D., Carlsen W. F. and Stryer L. (1978) Fluorescence Energy Transfer in the Rapid-Diffusion Limit, Proc. Nat. Acad. Sci. 75, 5746-5750. 

More related to general photochemistry are the papers which have appeared on wholly or partly diffusion-controlled reactions. The effect of a very short lifetime of the donor on the calculation of fluorescence quantum yields and lifetimes has been analysed by Viriot et al. Andre et al. analyse the kinetics of energy transfer to an acceptor when there are two different excited states capable of acting as donors and when interaction between these states is possible. The exchange interaction contribution to energy transfer between ions in the rapid diffusion limit... 

Energy transfer is typically measured by a decrease in the donor lifetime and, in the rapid diffusion limit, is a sensitive function of closest approach. Energy transfer based on a Forster dipole-dipole mechanism is proportional to a in three dimensions and a in two dimensions (e.g., on membranes), where a is the distance of closest approach. If the distance of closest approach is less than 10 or 11 A, energy transfer is dominated by a Dexter type exchange mechanism owing to overlapping wave functions between the donor and acceptor. The exact distance of closest approach then becomes difficult to measure. 

When using activation energies to estimate AH0, one must first demonstrate that the reactions, forward and reverse, are not limited by mass transfer or diffusion processes, which limits the application of this concept to external surfaces only under rapid solute-solid mixing. 

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