We report herein the first example of interpenetration isomerism in covalent organic frameworks (COFs). As a well-known three-dimensional (3D) COF, COF-300 was synthesized and characterized by the Yaghi group in 2009 as a 5-fold interpenetrated diamond structure ( dia-c5 topology). We found that adding an aging process prior to the reported synthetic procedure afforded the formation of an interpenetration isomer, dia-c7 COF-300. The 7-fold interpenetrated diamond structure of this new isomer was identified by powder X-ray diffraction and rotation electron diffraction analyses. Furthermore, we proposed a universal formula to accurately determine the number of interpenetration degrees of dia-based COFs from only the unit cell parameters and the length of the organic linker. This work not only provides a novel example to the category of interpenetration isomerism but also provides new insights for the further development of 3D COFs.

Understanding and controlling structural phase transitions in metal halide perovskites is important for designing stable and efficient optoelectronic devices. Using in situ nanoscale cathodoluminescence microscopy, we visualize the thermally driven transition to the perovskite phase in CsPbIBr 2 nanowires. Combined with molecular simulation, we reveal that the transformation proceeds despite a substantial energy barrier via ion diffusion through a liquid-like interface between the two structures. While cations disorder in this liquid-like region, the halide ions retain substantial spatial correlations to template the perovskite phase.

Nanostructured molybdenum oxides are promising materials for energy storage, catalysis, and electronic-based applications. Herein, we report the synthesis of MoO 3– x nanosheets ( x stands for oxygen vacancy) via an environmentally friendly liquid exfoliation approach. The process involves the reflux of the bulk α-MoO 3 precursor in water at 80 °C for 7 days. Electron microscopy and atomic force microscopy show that the MoO 3– x nanosheets are a few nanometer thick. MoO 3– x nanosheets exhibit near infrared plasmonic property that can be enhanced by visible light irradiation for a short time (10 min). Photocatalytic activity of MoO 3– x nanosheets for organic dye decolorization is examined using two different dyes (rhodamine B and methylene blue). Under visible light irradiation, MoO 3– x nanosheets make a rapid decolorization for the dye molecules in less than 10 min. The simple synthesis procedure of MoO 3– x nanosheets combined with their remarkable photochemical properties reflect the high potential for using the nanosheets in a variety of applications.