Resonance energy transfer Dexter mechanism

Details on the mechanisms and theories of excitation energy transfer via dipole-dipole interaction (FRET Forster resonance energy transfer) and via exchange interaction (Dexter s mechanism) can be found in B. Valeur, Molecular Fluorescence. Principles and Applications, Wiley-VCH, Weinheim, 2002, chap. 4 and 9. 

The occurrence of energy transfer requires electronic interactions and therefore its rate decreases with increasing distance. Depending on the interaction mechanism, the distance dependence may follow a 1/r (resonance (Forster) mechanism) or e (exchange (Dexter) mechanisms) [ 1 ]. In both cases, energy transfer is favored by overlap between the emission spectrum of the donor and the absorption spectrum of the acceptor. 

The Dexter Exchange Mechanism involves a direct contact between the donor and the acceptor atoms or molecules. The exchange interaction between the donor D and acceptor A involves a transition state with a D- A distance that is close to the sum of the gas-kinetic collision radii of D and A, respectively. Therefore, information about the energy transfer mechanism can be gained by structural studies of the system under consideration. If the D- A distance is short (normally < 5 A) then the exchange mechanism is the more likely, but if the D-A distance is long ( 5 A) then the resonance mechanism would be more likely. 

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