Xanthone. II. Vibronic coupling analysis from high resolution phosphorescence spectra

High resolved phosphorescence spectra of xanthone have been recorded in four host matrices in order to study vibronic coupling between the lowest tripl origin in all hosts, and the energetically close-lying second triplet state T₂, which is of nπ* orbital origin. In three hosts, there is thermall to phosphorescence from T₁. Vibrational analyses of the two emissions are reported. The vibrational structure of both emissions depends little on t vibronic mixing between the lowest two triplet states is weak, in spite of the small energy separation in some hosts. The importance of the different i ₁ and its sublevels is discussed, and it is concluded that across energy separations smaller than about 200 cm^?1 spin—orbit mixing is more orbital mixing between the ³ππ* and ³nπ* configurations of xanthone.