title: Energy dissipation processes of singlet-excited 1-hydroxyfluorenone and its hydrogen-bonded complex with N-methylimidazole.
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 pK(a) of 1HOF decreased from 10.06 to 5.0 on light absorption, and H(3)O(+) quenched the singlet-excited 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.
authors.affiliation: Chemical Research Center, Hungarian Academy of Sciences, Pusztaszeri út 59-67, 1025 Budapest, Hungary.
authors.forename: Krisztina
authors.initials: K
authors.lastname: Sebok-Nagy
authors.forename: László
authors.initials: L
authors.lastname: Biczók
authors.forename: Akimitsu
authors.initials: A
authors.lastname: Morimoto
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Shimada
authors.forename: Haruo
authors.initials: H
authors.lastname: Inoue
mesh_terms: D005449:Fluorenes / Q000737:chemistry*; D006860:Hydrogen Bonding; D006863:Hydrogen-Ion Concentration; D007093:Imidazoles / Q000737:chemistry*; D026082:Singlet Oxygen; D012997:Solvents; D013816:Thermodynamics
chemical_list: C494019:1-hydroxyfluorenone; D005449:Fluorenes; D007093:Imidazoles; D012997:Solvents; D026082:Singlet Oxygen; C018100:1-methylimidazole