Dexter excitation transfer

Dexter excitation transfer (Electron Exchange Excitation Transfer) Excitation transfer occurring as a result of an electron exchange mechanism. It requires an overlap... 

See also Dexter excitation transfer, Forster excitation transfer, radiative energy transfer, and spectral overlap. 

Baldo et al. [ 164] used the platinum complex of 2,3,7,8,12,13,17,18-octaethyl-21 //,23//-porphine (PtOEP, 66) as efficient phosphorescent material. This complex absorbs at 530 nm and exhibits weak fluorescence at 580 nm but strong phosphorescence from the triplet state at 650 nm. Triplet transfer from a host like Alq3 was assumed to follow the Dexter mechanism. Dexter-type excitation transfer is a short-range process involving the exchange of electrons. In contrast to Forster transfer, triplet exciton transfer is allowed. 

Energy transfer in solution occurs through a dipole-dipole interaction of the emission dipole of an excited molecule (donor) and the absorptive moment of a unexcited molecule (acceptor). Forster<40) treated the interaction quantum mechanically and derived and expression for the rate of transfer between isolated stationary, homogeneously broadened donors and acceptors. Dexter(41) formulated the transfer rate using the Fermi golden rule and extended it to include quadrupole and higher transition moments in either the donor or the acceptor. Following the scheme of Dexter, the transfer rate for a specific transition is... 

The cross-section of light absorption in processes (71) and (73) can be calculated according to eqns. (68) and (69), assuming d to be the dipole matrix element between the states A and A or B and B. The rate constants of processes (72) and (74) can be calculated with the help of the equations presented in the previous sections of this chapter. The rate constant of process (75) can be calculated using the formula which is the same as the well-known Forster-Dexter formula for electron excitation transfer [30],... 

The electron exchange (Dexter) mechanism which involves the overlap of wavefunctions of the donor and acceptor groups. This is a short-range excitation transfer mechanism that operates by... 

Electron exchange excitation transfer Same as Dexter excitation tranter. 

Both the Forster and the Dexter energy transfer mechanisms require spectral overlap of the donor emission spectrum and the acceptor absorption spectrum. However, energy transfer is known to occur even in the absence of spectral overlap, resulting in effective quenching of excited states. As an example, we can cite the quenching of the fluorescence of aromatic hydrocarbons by dienes, a process which involves thermal deactivation of an excited state encounter complex, or exciplex, between D and A (Eq. (3.7)) ... 

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