Energy transfer from the triplet state

Abstract

Energy transfer from the triplet level of a donor molecule resulting in quenching of the donor and elevation of the acceptor molecule from its singlet ground state to a triplet state has been observed between a number of donor-acceptor pairs in fluid solvents. In most cases the mechanism of the transfer has been unequivocally established by observation of the triplet state absorption spectra of both species. Energy transfer from excited singlet donors to the triplet state of the acceptor is not observed. When the energy of the acceptor triplet is considerably lower than that of the donor, transfer is diffusion-controlled but there is no evidence for long-range resonance transfer of the kind found in the analogous singlet energy transfer processes. As the triplet energies become comparable the transfer probability is reduced and no quenching is observed by molecules with triplet levels higher than that of the donor. Transfer of triplet energy between pairs of aromatic hydrocarbons has been illustrated and it has been established that complex formation between donor and acceptor cannot be important under the conditions of these experiments.