Mechanistic Insight into Hydrogen-Bond-Controlled Crystallinity and Adsorption Property of Covalent Organic Frameworks from Flexible Building Blocks

The effective control of crystallinity of covalent organic frameworks (COFs) and the optimization of their performances related to the crystallinity have been considered as big challenges. COFs bearing flexible building blocks (FBBs) generally own larger lattice sizes and broader monomer sources, which may endow them with unprecedented application values. Herein, we report the oriented synthesis of a series of two-dimensional (2D) COFs from FBBs with different content of intralayer hydrogen bonds. Studies of H-bonding effects on the crystallinity and adsorption properties indicate that partial structure of the COFs is “locked” by the H-bonding interaction, which consequently improves their microscopic order degree and crystallinity. Thus, the regulation of crystallinity can be effectively realized by controlling the content of hydrogen bonds in COFs. Impressively, the as-prepared COFs show excellent and reversible adsorption performance for volatile iodine with capacities up to 543 wt %, much higher than all previously reported adsorbents, although the variation tendency of adsorption capacities is opposite to their crystallinity. This study provides a general guidance for the design and construction of highly/appropriately crystalline COFs and ultrahigh-capacity iodine adsorbents.