Resonance Energy Transfer

The absorption of ultraviolet or visible light by an atom or molecule, resulting in its electronic excitation, is a familiar and staple photophysical process. Owing to the quantization of electronic states, the associated ultraviolet/visible absorption spectrum contains bands reflecting fixed energy gaps. It is of significant interest to ascertain the destination of the discrete energy held within an electronic excitation, and the mechanism by which the excitation arrives there. One such photodynamical process involves energy transfer from one molecule to another. This chapter gives an introduction to the key aspects of this energy transfer, from its photophysics to its applications to molecular biology. Formally, resonance energy transfer (RET) or electronic energy transfer (EET) is a photophysical process wherein excitation is transferred from an initially populated donor molecule to an acceptor molecule through intermolecular interactions. Traditionally, energy transfer within light-harvesting complexes is understood according to Förster RET theory.