Distant intramolecular interaction between identical chromophores: The n-π* excited states of p-benzoquinone

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Abstract
The structure and dynamics of the p‐benzoquinone n‐π* excited states have been investigated in solid Ne host. The two carbonyl excitations are essentially degenerate, with a B1g–Au splitting of +64 cm−1 between the singlets and −11 cm−1 between the triplets. There is no evidence that the lower 3B1g state has a double minimum potential via a pseudo Jahn–Teller distortion. The two triplets have very similar charge distributions and structures, despite their different formal symmetries. Excited singlet vibronic states show evidence for lifetime broadening due to intersystem crossing. Experiments in crystalline hosts are reviewed and reinterpreted. The structure in Ne host is closer to the intrinsic gas phase structure than are the structures in various single crystal environments. Valence bond theory, rather than molecular orbital theory, appears to be the natural description of the electronic structure.