Resonance energy transfer Forster theory

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 elucidation of the structure, dynamics and self assembly of biopolymers has been the subject of many experimental, theoretical and computational studies over the last several decades. [1, 2] More recently, powerful singlemolecule (SM) techniques have emerged which make it possible to explore those questions with an unprecedented level of detail. [3-55] SM fluorescence resonance energy transfer (FRET), [56-60] in particular, has been established as a unique probe of conformational structure and dynamics. [26-55] In those SM-FRET experiments, one measures the efficiency of energy transfer between a donor dye molecule and an acceptor dye molecule, which label specific sites of a macromolecule. The rate constant for FRET from donor to acceptor is assumed to be given by the Forster theory, namely [59,61-64]... 

Forster s theory [1], has enabled the efficiency of EET to be predicted and analyzed. The significance of Forster s formulation is evinced by the numerous and diverse areas of study that have been impacted by his paper. This predictive theory was turned on its head by Stryer and Haugland [17], who showed that distances in the range of 2-50 nm between molecular tags in a protein could be measured by a spectroscopic ruler known as fluorescence resonance energy transfer (FRET). Similar kinds of experiments have been employed to analyze the structure and dynamics of interfaces in blends of polymers. 

Strome and Klier 107,108) applied the Forster-Dexter theory of resonance energy transfer to explain these experimental observations, i,e., the energy transfer from the excited state of the Cu species to the coexistent... 

They found that Forster s theory of resonance energy transfer was applicable to such systems if the Interchromophoric distance and orientation, the fluorescence efficiency of the donor, the extinction of the acceptor, and the overlap between the emission of the donor and the absorption of the acceptor are of magnitudes which produce a transfer rate constant of less than 10 s and a transfer efficiency which is not too close to 0 or 1. 

Details on the mechanisms and theories of excitation energy transfer via dipole-dipole interaction (FRET Forster resonance energy transfer) and via exchange interaction (Dexter s mechanism) can be found in B. Valeur, Molecular Fluorescence. Principles and Applications, Wiley-VCH, Weinheim, 2002, chap. 4 and 9. 

Forster s theory is also behind the FRET method (Forster resonance energy transfer or fluorescence resonance energy transfer). In this case, excitation takes place with a narrow laser pulse, corresponding to the lowest excited state of a chromo-phore. The rate of EET is determined by time-resolved fluorescence. 

According to Forster s theory [13], the efficiency of the resonance energy transfer ( ret) is inversely proportional to the sixth-power of the distance (r) between donor and acceptor (2). In (2), Rq is the so-called Forster distance at which the transfer efficiency is 50%. Forster RET is therefore a very sensitive process and can transduce small conformational changes into large intensity modulations. Rq is characteristic for a particular donor-acceptor pair and depends on the overlap integral J between >ret emission and Aret absorption, the PLQY of >ret in its unperturbed state < d and the mutual orientation of the two partners expressed as geometry factor which equals 2/3 for random orientation of the partners (3). For a more detailed discussion of the mechanistics of RET, the reader is referred to the literature [12]. 

In 1948 Forster proposed a theory for the resonance energy transfer. He postulated that the rate of transfer depends on the inverse sixth power of the distance between the donor and the acceptor. This predicted distance dependence was verified later by experimental studies of fluorescent donor-acceptor pairs separated by a known distance in defined systems. 

A quantitative theoretical treatment was developed by Forster [39], who applied time-dependent perturbation theory to dipole-dipole interactions. The following is a simplified account. The probability of resonance energy-transfer from D to A at a distance R may be represented by a first-order rate parameter et (often, but inaccurately, called a rate constant), which is proportional to R and to the integral J representing the spectral overlap between the emission spectrum of the donor and the absorption spectrum of the acceptor. Forster s expression is ... 

Forster s theory of resonance energy transfer depends implicitly on thermal equilibration to trap the excitation on the acceptor. But the Forster theory is silent concerning the oscillations predicted by Eqs. (10.4a-10.5), and it does not address how rapidly the system equilibrates with the surroundings it simply assumes that equilibration occurs rapidly compared to the rate at which the excitation can return to the donor. 

According to the Forster theory of resonance energy transfer, which was proposed by T. Forster in 1959, energy transfer is efficient when... 

The theory of resonance transfer of electronic excitation energy between donor and acceptor molecules of suitable spectroscopic properties was first presented by Forster.(7) According to this theory, the rate constant for singlet energy transfer from an excited donor to a chromophore acceptor which may or may not be fluorescent is proportional to r 6, where r is the distance... 

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