Structure dependence of the photogeneration of thionaphthol triplets

In contrast to our findings on thiophenol and its substituted derivatives, thionaphthol triplet formation was found after UV photo-excitation in various solvents. The T1–Tn absorption spectra were characterized by a pronounced absorption band with λmax = 430–470 nm. The triplet states reactivity with triplet quenchers and their energy levels were determined. The triplet quantum yields were estimated to be 0.15 and 0.65 for 1-NpSH and 2-NpSH, respectively. The experimental results were interpreted by quantum calculations using the DFT B3LYP/6-311+G(d,p) method, which indicated that the small S1 − Tn=2,3 energy gap and different orbital configurations account for the direct triplet formation.