Forster energy exchange

The efficiency of Forster energy transfer depends mainly on the oscillator strength of the A -> A and B -> B radiative transitions, whereas the efficiency of energy transfer by the electron exchange interaction cannot be directly related to an experimental quantity. 

Keywords Oxalate networks [Cr(ox)3]3- [Cr(bpy)3]3+ 2E state Resonant energy transfer Phonon-assisted energy transfer Forster transfer Exchange interaction... 

The approaches to heterometaUic systems outlined above all rely upon coordination chemistry, whether to a metal ion or a nanoparticle surface. Supramolecular interactions can also play a role in assembling heterometaUic systems. For instance, Sambrook et al. prepared a pseudo-rotaxane (18) templated around a chloride ion (Fig. 9) in which lanthanide ions are bound to the thread while a luminescent rhenium complex is bound to the macrocycle component [49]. Thus there is no direct link between the donor chromophore and the lanthanide ion, and Dexter exchange is not viable in the absence of bonds enforcing Forster energy transfer. This extreme of behaviour helps to rationalize the behaviour of more conventionaUy... 

Figure 10 Orbital comparison of the coulombic (Forster) and exchange (Dexter) mechanism of electronic energy transfer [292],...

The occurrence of energy transfer requires electronic interactions and therefore its rate decreases with increasing distance. Depending on the interaction mechanism, the distance dependence may follow a 1/r (resonance (Forster) mechanism) or e (exchange (Dexter) mechanisms) [ 1 ]. In both cases, energy transfer is favored by overlap between the emission spectrum of the donor and the absorption spectrum of the acceptor. 

Figure 23. Two principal mechanisms of excitation energy transfer (EET). (a) The Forster dipole-dipole mechanism, in which the active electrons, one and two, remain, respectively, on D and A throughout the process, (b) In the (Dexter) exchange mechanism, electrons one and two exchange locations.

By substituting Eq. (B4.4.5) into Eq. (B4.4.7), we obtain the Forster rate constant kjl (Eq. 4.78 in the text) for energy transfer in the case of long-range dipole-dipole interaction, and substitution of Eq. (B4.4.6) into Eq. (B4.4.7) leads to the Dexter rate constant k fl (Eq. 4.85 in the text) for the short-range exchange interaction. 

As well as returning to the ground state by radiative or radiationless processes, excited states can be deactivated by electronic energy transfer. The principal mechanisms for this involve dipole-dipole interactions (Forster mechanism) or exchange interactions (Dexter mechanism). The former can take place over large distances (5 nm in favourable cases) and is expected for cases where there is good overlap between the absorption spectrum of the acceptor and the emission spectrum of the donor and where there is no change in the spin... 

A non-radiative energy transfer solely by dipole-dipole interactions - without recourse to electron exchange - from energy donor to an acceptor (Fig. 5.4) is described by the Forster mechanism. 

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