Cucurbit[8]uril-regulated face-to-face dimerization assembly enhanced photosensitization and photocatalysis

In water, N,N′-diarylpyridinium thiazolo[5,4-d]thiazole guests (G1–G3) were encapsulated by cucurbit[8]uril (Q[8]) to construct Q[8]₃/G₂ complexes, in which the encapsulated G molecules exist as an exact face-to-face dimer. These complexation behaviors have been indicated by proton nuclear magnetic resonance (¹H NMR) spectroscopy and isothermal titration calorimetry (ITC), and have been confirmed by X-ray single crystal structural analysis of Q[8]₃/G2₂. While free guests G1–G3 have no ability to sensitize singlet oxygen, they all become effective singlet oxygen sensitizers when complexed with Q[8]. By irradiation of white light, Q[8]₃/G₂ complexes induced selective oxidation of aryl sulfide to aryl sulfoxide in good yields and selective oxidation of dimethyl sulfide (DMS) to dimethyl sulfoxide (DMSO) in excellent yields without over-oxidation to dimethyl sulfone (DMSO₂) even for elongated irradiation. High-yield photo-oxidation of DMS to DMSO₂ was only achieved by irradiation of blue light in the presence of Q[8]₃/G1₂, which was also effective in photobleaching of Rhodamine B in water. The higher photo-oxidation power of Q[8]₃/G1₂ has been ascribed to an additional generation of reactive oxygen species besides singlet oxygen.