Robust Hexagonal 2D COF Single Crystals for the Construction of Porous Moiré Superstructures

We report a series of two-dimensional (2D) covalent organic framework (COF) single crystals with hexagonal pores and their exfoliation into single-crystalline thin films for the construction of porous Moiré superstructures. These 2D COF single crystals, COF-600, COF-660, and COF-666, with sizes up to 120 μm, exhibited isoreticular structure under the P65 space group, as determined by single-crystal X-ray diffraction (SCXRD) and electron diffraction (ED) with a resolution of up to 0.9 Å. A high density of weak interactions at the nodes of the 2D framework was key to maintain the structural integrity and porosity after exfoliation, allowing for the trapping of inorganic clusters within the pores. The thickness of the exfoliated films was tuned systematically from 50 nm to 1.5 μm. A transmission electron microscope (TEM) was used to unveil the porous structures of both the exfoliated films and the corresponding Moiré superstructures, with a resolution of up to 1.72 Å. Twisted angles covering the range from 2.1° to 30° were observed, among which the one with a twist angle of 30° gave a quasiperiodic Moiré pattern with 12-fold symmetry. The use of robust porous 2D COF single crystals for the construction of Moiré superstructures points to a new way to create 2D porous materials with hierarchical order. Such porous superstructures are likely to trigger the emergence of new physical and chemical properties.