Photophysical triplet state processes of 4H-1-benzopyrane-4-thione in a perfluoroalkane. Part 3.—Excitation-wavelength dependence of luminescence quantum yields
Abstract
The phosphorescence excitation spectrum of 4H-1-benzopyrane-4-thione (BPT) in perfluoro-1,3-dimethylcyclohexane coincides with the absorption spectrum in the range of the transitions S0→ T1 and S0→ S1. Hence the quantum yield ϕP of the phosphorescence from BPT is independent of the primary excited state, T1 or S1, in contrast to a reported lower value of ϕP for excitation to S1. The ratio ϕPF2/ϕP of the quantum yields ϕPF2 of the prompt S2→ S0 fluorescence and ϕP of the phosphorescence decreases with decreasing excitation wavelength.