Covalent organic frameworks (COFs) are a class of crystalline materials that can be made by linking organic building units with strong covalent bonds, and the building units themselves can be easily modified, resulting in materials with desired properties, such as high porosity and catalytic activity. By convention, these materials are constructed through directional bond formation between rigid molecular units, limiting their dynamic, mechanical and elastic properties.<br/>     Weaving materials, made by the interlacing of long threads in fabric, are flexible enough to be worn, but also robust enough to not be torn apart easily. The chemical analogue of this important design concept was realized for the first time by COF-505 using copper(I) ions as templates upon coordination with functionalized phenanthroline ligands to direct the formation of a crystalline weaving structure with atomically accurate precision. The copper(I) ions can be reversibly removed and added while preserving the structural integrity, for which a tenfold increase in elasticity accompanies the demetalation.<br/>     The successful design and synthesis of COF-505 could be the first step in the development of a large area of synthetic chemistry for weaving structures with various topologies and connectivities. The dynamical robust nature of weaving materials renders them to be easily processed due to their structural flexibility. With their chemical stability to boiling water and ammonia gas, these materials could be potentially used towards toxic gas adsorption and conversion, assisted and catalyzed by the metal centers in the flexible reactive microenvironment. The pore size can also be tailored isoreticularly to include target gases of varied sizes. Upon demetalation, these weaving material can be applied as responsive metal sponges, where the open phenanthroline sites have high affinities for common metal ions and can sequester them efficiently, the uptake of which can be measured by mechanical properties, such as hardness.

Molecular weaving of flexible covalent organic frameworks

253rd National Meeting (2017)

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