Electron-exchange mechanism

As the donor and acceptor molecules approach each other closely so that their regions of electron density overlap, electrons can be exchanged between the two molecules. This mechanism is therefore called the exchange mechanism. The electron-exchange mechanism requires a close approach (1-1.5nm), though not necessarily actual contact,... 

Table 6.1 Some energy-transfer processes by the electron-exchange mechanism allowed according to the Wigner spin conservation rule...

The question is Does the electron exchange mechanism involve the reproportionation-disproportionation reaction represented as in reaqtion 1 The apparent answer is that it... 

This transacetalization seems useful for intra or intermolecular glycosidation after photoirradiation of glucosides 17 in the same preceding conditions via a one electron exchange mechanism 1,6-anhydro sugar 18 or 2-deoxyglycoside 19 [a P = 55 45) are obtained in good yields (Scheme 10). 

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]. 

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

The interesting feature about these dioxetanes is that they possess easily oxidized groups, for example, 3-indolyl, / -dimethylanilinyl, and acridinyl " groups. Consequently, it has been proposed that these types of dioxetanes chemienergize 7T-rr singlet excited states by the intramolecular electron exchange mechanism. This topic will be discussed in detail in Section V.2. 

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. 

The electron-exchange properties of melanins have been studied with a number of special reagents in order to elucidate the electron exchange mechanism itself and the role of the melanin redox properties in biological systems. It was thus found that nitroxide radicals were reversibly reduced by melanins in the dark (5/9) and that the redox equilibria were altered on irradiation (see Section VI). Moreover, the reduction of nitroxides (R2NO ) was inhibited by oxygen. The equilibrium... 

Furthermore, the diffusion coefficients for triplet exciton migration extracted from this three-dimensional intramolecular model were nearly the same as those obtained using the conventional kinetic equation (i.e. eq 1). The hopping frequencies for triplet exciton migration in PVCA for these three models are summarized in Table 111(20). Neither the electron exchange mechanism(21) nor the Forster... 

Figure 2.17 Electron exchange mechanism for triplet energy transfer from 3D to A. The horizontal bars represent molecular orbital energies...

Alternately, Pt and WIG electrodes may respond in identical ways by completely different electron exchange mechanisms. This seems unlikely. Further work is necessary to determine which, if any, of these explanations is correct. 

---