The lowest nπ* and ππ* triplet levels of benzaldehydes and their correlation with the zero-field splittings

Abstract

The energies of the lowest nπ* and ππ* triplet states were determined for benzaldehyde and its derivatives in several hosts by measuring high-resolution phosphorescence and phosphorescence excitation spectra at 4·2 K. The energy separation between the nearly degenerate nπ* and ππ* triplet states was found to be linearly dependent upon the zero-field splitting. This supports our theory based on the spin-orbit interaction. From this linear relation, the spin-orbit coupling parameter, |G_z |, was obtained to be 9·1 cm^-1. This is the first quantitative study on the contribution of spin-orbit interaction to the zero-field splitting.