The Temperature Dependence of Fluorescence of Dibenzoanthrones

The fluorescence spectra of three isomeric dibenzoanthrones, 13H-dibenzo[a, de]anthracen-13-one (1), 13H-benzo[hi]chrysen-13-one (2), and 7H-dibenzo[a, kl]anthracen-7-one (3), in an ethanol-ether-toluene mixed solution were measured as a function of the sample temperature (T). The three molecules provided individual T-dependences of fluorescence spectra. The spectra of 1 changed usually, as T was decreased, they were intensified, showing a vibrational structure more clearly. 2 fluoresced very weakly and the spectra were almost insensitive to T; it also phosphoresced at low temperatures. The spectra of 3 exhibited only a broad band and, strangely enough, it was reduced with decreasing T. The peculiar T-dependence of the fluorescence spectra of 2 and 3 was explained in terms of the results obtained by molecular orbital calculations.