Viscosity and temperature dependence of fluorescence lifetimes of anthracene and 9-methylanthracene

Abstract

Time-correlated single-photon counting is used to determine the fluorescence lifetimes of anthracene and 9-methylanthracene over the temperature range 20-55°C as solutes in a variety of hydrocarbon solvents covering the viscosity range 0.3-200 cP (1 cP = 10-3 N s m-2). The absorption and emission spectra of both molecules show only small changes (e.g., 50 cm-1 shift in the absorption maxima) over this range of conditions. For anthracene, the fluorescence lifetime decreases with viscosity from a low viscosity limit; for 9-methylanthracene the fluorescence lifetime increases with viscosity and approaches a high viscosity limit. These results are quantitatively interpreted by a general kinetic ..