On the mechanism of triplet-singlet relaxation in phenanthrene

Abstract The phosphorescence spectrum of phenanthrene is discussed as being composed of two bands with relatively well-resolved vibronic structure separated by a common frequency interval of 1390 cm −1 . The first band can be understood by assuming the familiar spin-orbit coupling between a singlet and the lowest triplet state T 1 . The second band, however, is believed to be induced by an additional non-adiabatic channel for triplet-singlet relaxation which has an important influence on the total measured phosphorescence intensity. Good agreement is obtained between calculated and observed spectra.