TRIPLET BEHAVIOR OF ORGANIC COMPOUNDS

Abstract

Abstract— The rates of phosphorescence decay of nine compounds in frozen glass were measured. Six of the nine compounds decay exponentially, indicating that previously reported non‐exponential decay of some of them may have resulted from impurities, probably in the solvent.Three compounds – acetophenone, phenanthrene, and acridine orange–have unusual decay kinetics. Acetophenone has no wavelength–dependence of rate, but the decay is non‐exponential at all observed stages. The effect is believed due to a multiplicity of metastable excited states, all of which ultimately decay through a common lowest triplet. The delayed emission of phenanthrene in frozen glass consists of phosphorescence and a P‐type delayed fluorescence in the dimer band only. The ratio of the rates of decay of phosphorescence and delayed fluorescence is nearly the same in frozen glass as it is in liquid solution. It is suggested that excimers can be formed by molecules up to 100 A apart, and that the description ‘excited dimer’ is misleading. Finally, acridine orange has a P‐Type delayed fluorescence which decays initially with second‐order kinetics. The first‐order kinetics generally observed in P‐type delayed fluorescence are merely the result of the relative importance of competitive unimolecular reactions in depopulation of the triplet state.