Electron exchange excitation transfer

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

Electron exchange excitation transfer Same as Dexter excitation tranter. 

See electron exchange excitation transfer, Forster excitation transfer, radiative energy transfer. 

In electron exchange energy transfer, two electrons are simultaneously transferred between an excited state donor, D, and ground state acceptor, A (see Chap. 1). Orbital overlap is required, and, since electron density falls off rapidly with distance, electron exchange is restricted to intermolecular distances of <8 A. The spin conservation rule is obeyed and this mechanism is possible for both singlet-singlet and triplet-triplet energy transfer. 

Electron exchange energy transfer, which occurs when an excited donor molecule (D ) and an acceptor molecule A) are close enough (10-15 A) that they may be considered to be in molecular contact, i.e. their centres are separated by the sum of their molecular radii. Their electron clouds may overlap each other and an electron on D may also appear on A. 

For the fate of the excited states in condensed media, we must add to this list energy transfer processes. These are broadly classified as radiative (or trivial ), coulombic (mainly dipole-dipole interaction), or electron-exchange processes. 

In PET, an electron is transferred between an excited-state species and a ground-state species, and Figures 6.18 and 6.19 show that electron transfer processes occur by electron-exchange interactions and so require orbital overlap. 

Fig. 4.14. Schematic representation of the (A) Coulombic and (B) exchange mechanisms of excitation energy transfer. Cl Coulombic interaction EE electron exchange.

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. 

Figure 15 Calculated total and state-to-state excitation transfer cross sections in the de-excitation of He(2 P)-Ne. (From Ref. 151.) Both electron exchange and dipole-dipole interactions are included in the coupling matrix elements. The threshold energy into each exit channel is shown on the upper axis.

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