Substituent and solvent effects on the photophysical properties of 3-azafluorenone derivatives

Biczók, László and Cser, A. and Sebőkné Nagy, Krisztina (2001) Substituent and solvent effects on the photophysical properties of 3-azafluorenone derivatives. JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY, 146 (1-2). pp. 59-62. ISSN 1010-6030

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Abstract

Fluorescence lifetimes, fluorescence yields and triplet yields have been determined for 3-azafluorenone and its 7-substituted derivatives in various solvents. The energy of the lowest excited singlet state and the rate of intersystem crossing are found to be significantly higher in hexane relative to those in more polar solvents. The substitution with fluor and methyl groups as well as the solvent polarity enhancement considerably decelerate the triplet formation. This effect is attributed to the increase in the activation energy of the transition from the lowest singlet to a close-lying higher triplet excited state. The internal conversion gains in importance with increasing solvent polarity and becomes the major excited state depopulating process for the substituted derivatives in polar media. The changes in the internal conversion rate constants can be rationalized based on the energy gap law. © 2001 Published by Elsevier Science B.V.

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