On the dual phosphorescence of xanthone and chromone in glassy hydrocarbon hosts

Trace quantities of hydrogen-bonding impurities in otherwise highly purified and dried glassy hydrocarbon matrices at 77 K can modify the relative triplet state energy levels, and hence the photophysical properties of two aromatic ketones, xanthone and chromone, to the extent that the intrinsic spectroscopic properties are obscured. The intrinsic spectroscopic properties of each are revealed in multicrystalline n-alkane Shpol'skii matrices, and also can be observed in rigorously purified and dried hydrocarbon glasses at 77 K. The extreme sensitivity to stoichiometric, and even substoichiometric quantities of hydrogen-bonding impurities arises from the near-degeneracy of the two lowest-lying triplet states, and the sensitive nature of the n→π* blueshift phenomena to specific hydrogen-bonding interactions.