Forster resonance energy transfer calculator

Forster (1968) points out that R0 is independent of donor radiative lifetime it only depends on the quantum efficiency of its emission. Thus, transfer from the donor triplet state is not forbidden. The slow rate of transfer is partially offset by its long lifetime. The importance of Eq. (4.4) is that it allows calculation in terms of experimentally measured quantities. For a large class of donor-acceptor pairs in inert solvents, Forster reports Rg values in the range 50-100 A. On the other hand, for scintillators such as PPO (diphenyl-2,5-oxazole), pT (p-terphenyl), and DPH (diphenyl hexatriene) in the solvents benzene, toluene, and p-xylene, Voltz et al. (1966) have reported Rg values in the range 15-20 A. Whatever the value of R0 is, it is clear that a moderate red shift of the acceptor spectrum with respect to that of the donor is favorable for resonant energy transfer. 

Fluorescence resonance energy transfer (FRET) experiments commonly use the fluorescent spectrum and relaxation times of the Forster donor and acceptor chromophores to find the distances between fluorescent dyes at labeled sites in protein, DNA, RNA, etc. FRET is a type of spectroscopic ruler . The computation uses either experimental quantum yields or relaxation lifetimes to calculate the efficiency of resonance energy transfer Ej. 

Luminescence resonance energy transfer (LRET) proceeds by radiationless dipole-dipole coupled energy transfer from an excited luminophore through space to another lumino-phore [30]. There are several criteria that must be met for LRET. First, the emission band of the excited luminophore donor must overlap the absorbance band of the acceptor luminophore. The distance between the donor and acceptor molecules can be measured by using Equation 8.2 [31]. In Equation 8.2, the efficiency of energy transfer is E, tda is the time-resolved luminescence lifetime of the donor-acceptor pair, tq is the lifetime of the donor, Rq is the distance for 50% energy transfer to occur (or Forster distance), and r is the calculated distance between the donor and acceptor. 

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