Förster resonance energy transfer abbr., FRET; RET (rus. ферстеровский перенос энергии otherwise диполь-дипольный перенос энергии; флуоресцентный резонансный перенос энергии; индуктивно-резонансный перенос энергии) — energy transmission mechanism between two chromophores (from the donor to the acceptor), which occurs without intermediate photon emission and is the result of dipole-dipole interaction between the donor and the acceptor.


This phenomenon is named after the German physicist Theodor Förster, who, in 1946, was the first to write an article on the excitation energy transfer. Nonradiative energy transfer takes place from an excited donor to an acceptor through dipole-dipole interaction. 

A characteristic feature of this process is the quenching of donor fluorescence and the appearance of the longer-wavelength fluorescence of the acceptor. The speed of this process depends on the distance between the objects (decreasing as  r–6 ), and this makes it possible to measure the distance between two molecules and between the marks in a macromolecule. The effective distance where the transfer rate is 50% of the maximum is termed the Förster radius. For most systems, it amounts to 20-50 Å. 

The transfer rate also depends on the degree of donor emission and acceptor absorption spectra overlapping, on the relative orientation of donor and acceptor dipoles, and the lifetime of the excited state of the donor in the absence of the acceptor. 

The energy transfer efficiency (or the ratio of energy transfer events to the donor's excitations) is directly related to the transfer rate and has the same dependence on the distance between the objects (decreasing as  r–6 ). 

The energy transfer phenomenon enables the study of macromolecule structures and the evaluation of intermolecular interactions and the rate of biochemical reactions. It is widely used in biochemistry, molecular biology, biotechnology, and medicine. 


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Intramolecular energy transfer in a protein molecule.



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