Stryer, L.
Fluorescence energy transfer as a spectroscopic ruler. Annual Reviews of Biochemistry 47: 819-846 (1978).

Electronic excitation energy can be efficiently transferred between a fluorescent energy donor and a suitable energy acceptor over distances as large as 70 Å. In 1948, Förster (1) proposed a theory for this dipole-dipole energy transfer process which postulated that the rate of transfer depends on the inverse sixth power of the distance between the donor and acceptor. This predicted distance dependence was verified by fluorescence studies of donor acceptor pairs separated by a known distance in well-defined model systems (2-4). Stryer & Haugland (3) then suggested that energy transfer could be used as a spectroscopic ruler in the 10-60 Å range to reveal proximity relationships in biological macromolecules.