The observation of emission from benzophenone1•2 and acetophenone2 in fluorocarbon1 and hydrocarbon2 solvents represents a substantial breakthrough in the study of photochemical processes in solution. In the following we show that the emission from several aromatic ketones is composed of delayed fluorescence and phosphorescence components.Sources of materials and purification methods will be described in the full paper. Solutions of the ketones in carbon tetrachloride or benzene were outgassed to < 10~6 mm using 5-7 freeze-pump-thaw cycles. Emission spectra were recorded using a Hitachi Model MPF-2A spectrophotometer (Phototube, Hitachi -06). Corrected spectra and emission quantum yields were determined using quinine bisulfate as standard, ¥ = 0.56. [3][4][5] The emission spectrum of benzophenone in carbon tetrachloride at 23°is typical (Figure 1). It agrees well with the spectra obtained in benzene, perfluoromethylcyclohexane,1 and isooctane.2 The positions of phosphorescence 0-0 bands and the corresponding triplet excitation energies are given in Table I. These energies are 1-2 kcal/mol lower than those obtained from measurements in hydrocarbon glass at 77°K.6 For the benzophenones a plot of £T against Hammett's is (1) C. A. Parker, Chem. Commun., 749 (1968).

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Anhand der Emissionsspektren der Ketone (I) und (II) in Benzol oder Tetrachlorkohlenstoff wird die Aktivierungsenergie ihrer Triplettzustände berechnet sowie eine verzögerte Fluoreszenz festgestellt.