SUBSTITUENT, SOLVENT, AND TEMPERATURE EFFECTS ON RADIATIVE AND NONRADIATIVE PROCESSES OF SINGLET EXCITED FLUORENONE DERIVATIVES

Fluorescence lifetimes, fluorescence quantum yields, and triplet yields have been measured for 2-fluorofluorenone and 2-methoxyfluorenone in different solvents having a wide range of polarities. The photophysical characteristics of the fluoro derivative were found to be similar to those of fluorenone itself. The dominating process in nonpolar and moderately polar solvents is singlet-triplet transition with temperature-independent and additional temperature-dependent components. However, the photophysics of the methoxy derivative is governed by internal conversion to the ground state, which gains in importance with increasing solvent polarity and shows a temperature-dependent rate in nonpolar solvent. The efficient internal conversion is explained by assuming the decay to occur from a charge-transfer-type excited state.