To create a new series of mechanofluorochromic materials and to elucidate the mechanism of the phenomenon of mechanofluorochromism, 1-alkanoylaminopyrenes including 1-acetylaminopyrene (AAPy), 1-octanoylaminopyrene (OAPy), and 1-stearoylaminopyren (SAPy) were prepared. It was found that these materials exhibited mechanofluorochromism with emission colors in the crystalline samples changing reversibly from bluish purple to yellowish green, which could be induced by mechanical grinding. X-ray crystal structure analysis, electronic absorption, and fluorescence spectroscopies, as well as fluorescence lifetime analysis and powder X-ray diffraction analysis of AAPy suggested that the present mechanofluorochromism was caused by developing crystal defects through grinding. Intermolecular hydrogen bonds were suggested to play an important role in the occurrence of mechanofluorochromism, suppressing the face-to-face overlapping of pyrene moieties to form excimers in the pristine crystal.

We recently reported the synthesis of a solid-state heterojunction photocatalyst consisting of zinc rhodium oxide (ZnRhO) and bismuth vanadium oxide (BiVO), which functioned as hydrogen (H) and oxygen (O) evolution photocatalysts, respectively, connected with silver (Ag). Polycrystalline BiVO (p-BiVO) powders were utilized to form ZnRhO/Ag/p-BiVO, which was able to photocatalyze overall pure-water splitting under red-light irradiation with a wavelength of 700 nm (R. Kobayashi et al., J. Mater. Chem. A, 2016, 4, 3061). In the present study, we replaced p-BiVO with a powder obtained by pulverizing single crystals of BiVO (s-BiVO) to form ZnRhO/Ag/s-BiVO, and demonstrated that this heterojunction photocatalyst had enhanced water-splitting activity. In addition, ZnRhO/Ag/s-BiVO was able to utilize nearly the entire range of visible light up to a wavelength of 740 nm. These properties were attributable to the higher O evolution activity of s-BiVO.

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A hierarchical Z-scheme photocatalyst composed of BiVO4, ZnRh2O4, and Au was synthesized for visible-light-induced water splitting.