Energy dissipation processes of singlet-excited 1-hydroxyfluorenone and its hydrogen-bonded complex with N-methylimidazole

Sebőkné Nagy, Krisztina and Biczók, László and Morimoto, A. and Shimada, T. and Inoue, H. (2004) Energy dissipation processes of singlet-excited 1-hydroxyfluorenone and its hydrogen-bonded complex with N-methylimidazole. PHOTOCHEMISTRY AND PHOTOBIOLOGY, 80 (1). pp. 119-126. ISSN 0031-8655

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Abstract

Effects of solvent, pH and hydrogen bonding with N-methylimidazole (MIm) on the photophysical properties of 1-hydroxyfluorenone (1HOF) have been studied. Fluorescence lifetime, fluorescence quantum yield and triplet yield measurements demonstrated that intersystem crossing was the dominant process in apolar media and its rate constant significantly diminished with increasing solvent polarity. The acceleration of internal conversion in alcohols paralleled the strength of intermolecular hydrogen bonding. The faster energy dissipation from the singlet-excited state in cyclohexane was attributed to intramolecular hydrogen bonding. The pKa of 1HOF decreased from 10.06 to 5.0 on light absorption, andH3O1 quenched the singletexcited molecules in a practically diffusion-controlled reaction. On addition of MIm in toluene, dual fluorescence was observed, which was attributed to reversible formation of excited hydrogen-bonded ion pair. Rate constants for the various deactivation pathways were derived from the combined analysis of the steady-state and the time-resolved fluorescence results.

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