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 ϕ_P of the phosphorescence from BPT is independent of the primary excited state, T₁ or S₁, in contrast to a reported lower value of ϕ_P for excitation to S₁. The ratio ϕ_PF2/ϕ_P of the quantum yields ϕ_PF2 of the prompt S₂→ S₀ fluorescence and ϕ_P of the phosphorescence decreases with decreasing excitation wavelength.