Assignment and analysis of the absorption and emission spectra of the lowest nπ* triplet state in 9,10-anthraquinone

Polarized Zeeman absorption experiments on 9,10-anthraquinone crystals show the lowest triplet state in this molecule to be a g nπ^* state. The gap between this state and the higher u nπ^* state is found to be 410 cm^?1. The phosphorescence spectrum of an isotopically mixed crystal of AQ-h₈ in AQ-d₈ is analyzed in detail and confirms the orbitally forbidden nature of the emitting state. The results are compared with those previously obtained for p-benzoquinone.