http://worldcat.org/entity/work/id/137242505

Radiationless deactivation and anomalous fluorescence of singlet 1,12 benzperylene

Values of the rate constants for processes that deactivate the lowest excited singlet state of 1,12 benzperylene were determined between -196C and 23C from measurements of the quantum yields of triplet formation, fluorescence, and the fluorescence lifetime. The rate constant for intersystem crossing to the triplet state is nearly same at -196C and +23C. The rate constant for direct radiationless deactivation to the lowest singlet is probably zero at -196C but increases to 600000/sec at +23C. This is similar to results obtained for other aromatic hydrocarbons. However, the fluorescence of 1,12 benzperylene is atypical. An increase in the rate constant of fluorescence, k1, from -196C to +23C is observed resulting from an increase in fluorescence with temperature while fluorescence lifetime decreases over the same temperature range. The increase in k1 with increasing temperature is attributed to a temperature dependent emission from the second excited singlet state. Since the second excited singlet state of 1,12 benzperylene lies only 1275 to 1400/cm above the (1)Lb state, there is significant thermal population of the (1)La state of +23C. The observation of a temperature dependent anti stokes fluorescence supports this interpretation. The effect of solvent upon the energy gap between the (1)La and (1)Lb state and the fluorescence properties of 1,12 benzperylene is discussed. (Author).

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