Mechanism Dexter electron exchange

Given that triplet-triplet energy transfer proceeds via a Dexter (electron exchange) mechanism, it is not surprising that electron transfer can also occur via upper triplet states. Two-color experiments with anthracene in acetonitrile in the presence of ethylbromoacetate, a dissociative electron acceptor, showed that excitation to an upper triplet state led to depletion of the T-T absorption and concurrent production of the anthracene cation radical as a result of electron transfer (Scheme 1) [52]. 

Increasing Q, would decrease the average minimum distance between a self localized PFq.fast excitation and a possible CTS defect, which suggests that Eq. 4, simply describes the qualitative dependence with distance for the Dexter electron exchange mechanism k j = ko e R, where ko is the maximum rate constant for energy transfer, occurring when donor and acceptor are at the collision distance Ro and R is the separation between donor and acceptor when they are further apart than Ro. 

ET proceeds by a Dexter electron exchange mechanism and is a weakly coupled non-adiabatic process. Its rate constant kET can be approximated by the Golden Rule " " ... 

Figure 2.14 Schematic representations of the mechanisms of photoinduced (a) electron transfer, (b) Dexter (electron-exchange) energy transfer, and (c) Fdrster (dipole-dipole) energy transfer mechanism processes in the supramolecular dyad A-L-B spheres represent electrons, while curved arrows indicate the directions of transfer...

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

From Eq. (3.6) we observe that the rate of energy transfer by electron exchange mechanism decreases exponentially with 2R/L. Thus, it will be negligibly small as R increases more than on the order of one or two molecular diameters. Hence the effective distances for Dexter energy transfer range between 10 and 15 A. 

The Dexter or electron exchange mechanism of energy transfer. 

One can see tliat tlie Dexter exchange mechanism is exponentially dependent on tlie distance between tlie donor and acceptor, and as such it begins to play a visible role only at very short distances when tlie electron clouds begin to... 

Figure 23. Two principal mechanisms of excitation energy transfer (EET). (a) The Forster dipole-dipole mechanism, in which the active electrons, one and two, remain, respectively, on D and A throughout the process, (b) In the (Dexter) exchange mechanism, electrons one and two exchange locations.

Calixarene containing a dioxotetraaza unit, PET-18, is responsive to transition metal ions like Zn2+ and Ni2+. Interaction of Zn2+ with the amino groups induces a fluorescence enhancement according to the PET principle. In contrast, some fluorescence quenching is observed in the case of Ni2+. PET from the fluorophore to the metal ion is a reasonable explanation but energy transfer by electron exchange (Dexter mechanism) cannot be excluded. 

Figure 3.36 The Dexter mechanism of energy transfer through simultaneous electron exchange.

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... 

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