Quenching of triplet states of organic compounds by coordination complexes

Abstract

Recent evidence which establishes that electronic energy transfer is the most common mechanism for quenching of organic triplet states by coordination compounds is discussed. It is pointed out that only when energy transfer produces ligand field excited states is there likely to be markedly different behaviour observed from that expected for a typical organic triplet energy acceptor. Transfer to produce internal ligand and ligand to metal or metal to ligand charge-transfer excited states is not expected to show any differences other than the occurrence of spin statistical factors and these probably only when transfer produces excited charge transfer states. New evidence is presented that triplet state quenching by ferrocene, tris(acetylacetonate) iron(III), FeIII(acac)3, and tris(dipivaloylmethanate) iron(III), FeIII(dpm)3, is due to electronic energy transfer. For these quenchers a high degree of correlation between their spectroscopically determined energy levels and plots of the quenching rate constants as a function of the energy of the triplet state being quenched is demonstrated. It is suggested that the use of such quenching plots in conjunction with stereochemical and spectroscopic information concerning the excited states which are energetically available to accept electronic excitation energy is likely to allow progress to be made in establishing the determining parameters which govern triplet energy transfer to produce ligand field excited states in coordination compounds. © 1975, Walter de Gruyter. All rights reserved.