Electronic energy transfer Forster

In this chapter we shall first outline the basic concepts of the various mechanisms for energy redistribution, followed by a very brief overview of collisional intennoleciilar energy transfer in chemical reaction systems. The main part of this chapter deals with true intramolecular energy transfer in polyatomic molecules, which is a topic of particular current importance. Stress is placed on basic ideas and concepts. It is not the aim of this chapter to review in detail the vast literature on this topic we refer to some of the key reviews and books [U, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, and 32] and the literature cited therein. These cover a variety of aspects of tire topic and fiirther, more detailed references will be given tliroiighoiit this review. We should mention here the energy transfer processes, which are of fiindamental importance but are beyond the scope of this review, such as electronic energy transfer by mechanisms of the Forster type [33, 34] and related processes. 

Self-assembly of functionalized carboxylate-core dendrons around Er +, Tb +, or Eu + ions leads to the formation of dendrimers [19]. Experiments carried out in toluene solution showed that UV excitation of the chromophoric groups contained in the branches caused the sensitized emission of the lanthanide ion, presumably by an energy transfer Forster mechanism. The much lower sensitization effect found for Eu + compared with Tb + was ascribed to a weaker spectral overlap, but it could be related to the fact that Eu + can quench the donor excited state by electron transfer [20]. 

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... 

In what follows we derive the Forster expression for the rate of electronic energy transfer between two chromophore molecules. We consider two such molecules, donor D and acceptor A, each represented by its ground and excited electronic states and the associated vibrational manifolds Id, 2D,/j ° ) forthe ground and excited state manifolds of molecule D and 1a, 2a,... 

The theory of electronic energy transfer in terms of a dipole-dipole interaction has been developed by Forster (4). In this theory the rate constant for energy transfer, ko-A, is given by... 

The shape of the decay profile of an excited donor is determined, amongst other parameters, by the distribution profile of the surrounding acceptors. Thus, the classical three dimensional Forster equation for non-collisional, one step electronic energy transfer (ET), had to be modified for the case of a two dimensional arrangement of donors and acceptors (35). This has been generalized recently, to include not only two and three dimensional acceptor distributions, but also D-dimensional distributions (36) ... 

The value of E calculated from the quantum yield is higher than that measured from the lifetime. Therefore, fluorescence lifetimes of Trp residues of ai-acid glycoprotein are the result of an energy transfer Forster type or by electron transfer to neighboring amino acids and of the molecular collisions of the Trp residues with their environments. 

Electronic energy transfer (EET) Forster resonance energy transfer (FRET)... 

Curutchet C, Mennucci B, Scholes GD, Beljonne D (2008) Does Forster theory predict the rate of electronic energy transfer for a model dyad at low temperature J Phys Chem B 112 3759... 

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

The process is often referred to as Dexter energy transfer, after David L. Dexter who, following on from earlier work by Forster, developed a detailed quantitative description of the various couphng mechanisms involved in electronic energy transfer [64]. The relevant equation in its simplest form is ... 

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. 

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