Forster-type coulombic interactions

The energy transfer processes can occur by two mechanisms the Forster-type mechanism (through-space) [55], based on coulombic interactions, and the Dexter-type mechanism (through-bond) [56], based on exchange interactions. The energy transfer rate constants according to the Forster and Dexter treatments can be evaluated by Eqs. (4) [55] and (5) [56], respectively ... 

Dexter- or a Coulomb-type energy transfer mechanism. However, the second step is a temperature-independent transfer, which could be attributed to a Forster dipole-dipole interaction type [42],... 

All of the examples of singlet energy transfer we have considered take place via the long-range resonance mechanism. When the oscillator strength of the acceptor is very small (for example, n ir transitions) so that the Forster critical distance Ro approaches or is less than the collision diameter of the donor-acceptor pair, then all evidence indicates that the transfer takes place at a diffusion-controlled rate. Consequently, the transfer mechanism should involve exchange as well as Coulomb interaction. Good examples of this type of transfer have been provided by Dubois and co-workers. " ... 

Let us consider the simple case of two ions, each with one excitable electronic state separated from its electronic ground state by nearly equal energy. With suitable interaction between the two electronic systems, the excitation will jump from one ion to the other before a quantum of fluorescence is emitted. The systems interact by Coulomb interactions of the Van der Waals type. Forster (1948), who first treated such a case by quantum-mechanical theory, considered the dipole-dipole interactions. He assumed that the interaction is strongest if, for both transitions, electric-dipole transitions are allowed (Forster 1960). The interaction energy (//sa) is then proportional to the inverse of the third power of the interionic distance, and the transfer probability is given by... 

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