Mechanisms of Energy Transfer

Abstract

The energy transfer processes could be classified as follows: (a) The energy transfer could be a short-range (distances of several Angstroms) and a long-range (distances up to several tens of Angstroms). In short distances the electronic clouds of the donor and acceptor are sufficiently overlapped. In long distances the overlap is small. The smaller is the donor-acceptor distance, the more efficient is the energy transfer. (b) The energy transfer is occurred due to strong or weak interactions. Under strong interactions between the donor in the ground state and the acceptor the absorption spectra are modified. Under weak interactions the absorption spectra are changed insignificantly. Usually, interaction between the excited donor and the acceptor is strong. (c) The energy transfer could be singlet-singlet, triplet-triplet, singlet-triplet, and triplet-singlet, depending on the spin state of the donor and acceptor. (d) The energy transfer could be «hot» and «cold». If the rate constant of the transfer is not less than that of the vibrational relaxation in the donor, this is a hot transfer. If the rate constant is less, the transfer is a cold. When transfer is hot, the sensitized and individual lifetimes are equal tacking into account the rate constant of vibrational relaxation of the donor. When energy transfer is cold, the lifetime of sensitized acceptor emission is approximately equal to the sum of acceptor own lifetime and the donor lifetime. (e) The energy transfer could be direct and reverse. If the electronic excitation transferred to the acceptor returns to the donor, this is a reverse transfer. (f) The energy transfer could be of Coulomb or exchange nature. (g) The energy transfer could be total (resonant) and fractional (non-resonant). If a quantum of energy is transferred from the donor as a whole, this is a total transfer induced by resonance between electronic levels of the acceptor and the excited donor. If only a part of the energy is transferred, this is a fractional transfer.