Resonance energy transfer Coulomb interaction

It is useful in discussion of weak coupling between nanostructures to remember the nonradiative mechanism of Forster resonant energy transfer from an excited molecule (a donor) to some other molecule (an acceptor) which can be in the ground or in an excited state. The probability of such a transfer is determined by the Coulomb nonretarded (instantaneous) dipole-dipole interaction between molecules and is proportional to Rp/R6 where Rp is the Forster radius and R is the distance between molecules. For organic materials the Forster radius is usually about several nanometers and strongly depends on the overlapping... 

The total coulombic interaction includes dipole—dipole, dipole— quadrupole and higher multipole interactions. Forster [164] in a quantum mechanical treatment of resonance energy transfer which takes place between two well-separated molecules has considered only dipole—dipole interaction. A quantitative treatment leads to the following equation for the transfer rate coefficient [164] ... 

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 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. 

Resonance-excitation (dipole-dipole) energy transfer, which occurs when an excited donor molecule (D ) transfers its excitation energy to an acceptor (A) molecule over distances much greater than collisional diameters (e.g. 50-100 A). In this mechanism energy transfer occurs via dipole (donor)-dipole (acceptor) interaction (Coulombic interaction). When an acceptor (A) is in the vicinity of an excited donor (D ) (an oscillating dipole), it cause electrostatic forces which can be exerted on the electronic system of an acceptor. 

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