Effect of water on the phosphorescence spectra of aromatic carbonyl compounds. Part 2.—Dual phosphorescence of benzophenone at 77 K in ethanol–water

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Abstract
The phosphorescence spectrum of benzophenone (BP) at 77 K in the mixed solvents of ethanol (EtOH) and water exhibits dual phosphorescence of normal nπ* character with short (5.6 ms) and long (8.0 ms) lifetimes. In comparison with the result in 2,2,2-trifluoroethanol (TFE)–H2O, the present result indicates that the short-lived component is free triplet BP and the long-lived component is a complex of triplet BP–H2O (1 : n) with a fixed number of n. For complex formation, even such a strong hydrogen-bonding solvent as TFE is not a special solvent, but the existence of a small amount of water is essential.