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

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