Coulombic mechanism, energy transfer

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-> n transitions) so that the Fdrster critical distance R0 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.(47-49)... 

The Coulombic mechanism is a relatively long-range process in as much as energy transfer can be significant even at distances of the order of lOnm. 

In order for rapid and efficient energy transfer to occur by the Coulombic mechanism ... 

A detailed theory of energy transfer by the Coulombic mechanism was developed by Forster, so the process is often referred to as Forster resonance energy transfer (FRET). According to the Forster theory, the probability of Coulombic energy transfer falls off inversely with the sixth power of the distance between the donor and the acceptor. For... 

The Coulombic mechanism would require that both 3D — 3D and 1A —> 3A were allowed transitions, which clearly they are not as both are spin-forbidden processes. Thus, triplet-triplet energy transfer by the long-range Coulombic mechanism is forbidden. 

The energy transfer occurs by means of the Coulombic long-range mechanism (Section 6.6), which ultimately redistributes the excitation energy via the adjacent pigment molecules to the reaction centre. Excitation of the reaction centre is over within a few femtoseconds. 

Energy transfer can result from different interaction mechanisms. The interactions may be Coulombic and/or due to intermolecular orbital overlap. The Coulombic interactions consist of long-range dipole-dipole interactions (Forster s... 

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

Since the cross section for nonrelativistic Coulomb scattering is the same in classical and quantum mechanics, equation (2) must contain much of the essential physics in the slowing-down process. However, it also contains an undetermined minimum energy transfer rmin which is nominally zero and hence leads to an infinite stopping force. 

This exciton diffuses to the donor/acceptor interface via an energy-transfer mechanism (i.e., no net transport of mass or charge occurs). (3) Charge-transfer quenching of the exciton at the D/A interface produces a charge- transfer (CT) state, in the form of a coulombically interacting donor/acceptor complex (D A ). The nomenclature used to describe this species has been relatively imprecise, and has... 

Figure 11.5 Diagrammatic explanation of the coulombic and electron exchange energy transfer mechanisms (A and B are chromophore components and L is a bridging moiety or ligand).

The Forster mechanism is also known as the coulombic mechanism or dipole-induced dipole interaction. It was first observed by Forster.14,15 Here the emission band of one molecule (donor) overlaps with the absorption band of another molecule (acceptor). In this case, a rapid energy transfer may occur without a photon emission. This mechanism involves the migration of energy by the resonant coupling of electrical dipoles from an excited molecule (donor) to an acceptor molecule. Based on the nature of interactions present between the donor and the acceptor, this process can occur over a long distances (30—100 A). The mechanism of the energy transfer by this mechanism is illustrated in Figure 11. 

Fig. 3.7 Pictorial representation of resonance (coulombic) and exchange energy transfer mechanisms...

The most convincing demonstration of the importance of the Coulombic relay mechanism, or a bridge-exciton-mediated singlet energy transfer, comes from the... 

It is worth noting that while Dexter s name became synonymous with the exchange mechanism of energy transfer, the main body of his seminal paper is devoted to spin-allowed EET mediated by the various multipole terms of the Coulomb interaction. 

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