Vibronic Spin—Orbit Interactions in Heteroaromatic Molecules. I. Polycyclic Monoazines

The phosphorescence of several polycyclic monoazines is more in-plane polarized in hydrocarbon solvents than in hydroxyl solvents outside the 0,0 band. The results are attributed to the solvent effect on the second-order spin—orbit coupling involving vibronic interactions between n, π* and π, π* electronic states. It is suggested that the solvent effect on the vibronic spin—orbit interactions is partly responsible for the solvent dependence of phosphorescence lifetime. The solvent effects on the fluorescence and intersystem crossing of heteroaromatic molecules are examined and discussed in light of these results.