Subsequently, product 8 could be obtained in 36% yield when the reaction mixture of S8 and H1 was irradiated with a higher energy light source (λ max = 365 nm) in the absence of any photocatalyst, indicating that the SET events are unlikely in this transformation (Fig. ). Then, UV-vis absorption spectroscopy of all reactants and their mixtures were measured, and thioxanthone was found to be the only absorbing species in the reaction near the irradiation wavelength (λ max = 405 nm) (Fig. ). Moreover, Stern-Volmer analysis demonstrated that the luminescence emission of thioxanthone was quenched efficiently by S8 rather than H1, implying that an interaction between thioxanthone and S8 might exist in the reaction medium (Fig. ). To understand the nature of their interaction, comparison of some photocatalysts with different properties was conducted (Fig. ). As a result, yields of product 8 correlate to the triplet state energy of photocatalysts, while they are unrelated to the redox properties. These results implied that an energy transfer (EnT) process is likely to be operative in the reaction. Furthermore, the cyclic voltammetry measurement was conducted. As shown in Fig. , no obvious oxidation peak of S8 and H1 was observed before +1.4 V vs SCE, which suggest that these two compounds could not be oxidized by the excited state *thioxanthone (E 1/2