Förster excitation transfer (dipole–dipole excitation transfer)

A mechanism of excitation transfer which can occur between molecular entities separated by distances considerably exceeding the sum of their van der Waals radii. It is described in terms of an interaction between the transition dipole moments (a dipolar mechanism). The transfer rate constant is given by: where is an orientation factor, the refractive index of the medium, the radiative lifetime of the donor, the distance (cm) between donor (D) and acceptor (A), and the spectral overlap (in coherent units ) between the absorption spectrum of the acceptor and the fluorescence spectrum of the donor. The critical quenching radius, , is that distance at which is equal to the inverse of the radiative lifetime.