Sublevel phosphorescence spectra of anthraquinone. I. Site selective sublevel phosphorescence spectra for octane and hexane solutions

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Abstract
The sublevel phosphorescence spectra originating from individual sites are observed. The sublevel phosphorescence spectra obtained have vibrational structures which are quite simple as compared with the complicated structures usually found in multisite and thermally averaged phosphorescence spectra. The vibrational analysis can be performed straightforwardly. The Tz spectrum has vibronic bands due to b1u vibrations only. These vibronic bands are mainly due to the vibronic coupling between the 3B1g(nπ*) lowest triplet state with a closely located 3Au(nπ*) state. The Tx spectrum has vibronic bands involving b3u vibrations only. The intensity mainly comes from a mechanism which involves vibronic coupling between 1B2g(σπ*) and 1B1u(ππ*). The Ty phosphorescence spectrum has vibronic bands involving b2u vibrations only. The intensity comes from a mechanism which involves vibronic coupling between 3B1g(nπ*) and 3B3u(σπ*). The rigorous selectivity in the appearance of vibronic bands in the sublevel phosphorescence spectra reveals that the molecule retains its D2h symmetry in the triplet state. This conclusion contradicts with the one given by Khalil and Goodman. Finally some comments are made concerning previously given vibrational assignments.

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