Energy Migration

the spontaneous transfer of energy from one particle (the donor—an atom or molecule) to another (the acceptor).

Energy migration is connected neither with the emission of a photon by the donor and its absorption by the acceptor nor with the exchange of electrons or atoms between interacting particles. It results from the electromagnetic interaction of particles (the inductive-resonance mechanism) or the partial overlapping of their electron shells (the exchange-resonance mechanism). Various forms of energy can migrate, but energy migration is most often observed after the transition of a molecule (or atom) to an electron-excited state upon absorption of a photon. In the time before the reverse process of radiation of light takes place and the molecule is in an excited state, it can transfer the energy it has received to another molecule that is sufficiently close—that is, at a distance less than the wavelength of the corresponding radiation (<80 angstroms). In a condensed medium (solutions or crystals) such transfer takes place repeatedly, and the energy may be displaced over comparatively large distances (several microns) from the point of absorption of the photon. Energy migration takes place in gases, liquids, and solids. S. I. Vavilov showed that energy migration explains such phenomena as concentration depolarization and concentration quenching of the luminescence of dyes in solution.

Energy migration plays a major role in biological systems by participating in many processes of vital activity. Migration of the energy of electron excitation is particularly important in photobiology. For example, in the process of photosynthesis a quantum of light places a molecule of chlorophyll or another pigment in an electron-excited state. The energy then migrates from one molecule of the pigment to another until it reaches a particular molecule, which serves as a reaction center that converts the energy of electron excitation into chemical energy (that is, into energy contained in chemical bonds).

In addition to intermolecular energy migration, intramolecular energy migration is also possible. For example, the migration of energy between individual nitrogen bases apparently takes place in the DNA or RNA molecule upon absorption of a quantum of ultraviolet radiation. This may play a role in the damaging action of shortwave radiation on cells and viruses. A second example of the intramolecular migration of energy is the transfer of the energy of a photon in the nicotinamide adenine dinucleotide (NAD) molecule from the adenine group to the nicotinamide group.