Spin—lattice relaxation processes in photo-excited triplet states through a rotation of the spin axes on thermal excitation

Abstract

We have observed a temperature dependence of the direction of the principal axes of the zero-field splitting for the triplet state of naphthalene in durene. The effect is caused by thermal excitation to a nearby local phonon state, where the spin axes are rotated with respect to those in the lowest triplet state. With the help of a simple model we can give a satisfactory explanation of the spin—lattice relaxation process in the lowest triplet state as a result of the thermal excitation to the low lying phonon state.