Single-crystal one-dimensional porous covalent organic frameworks

One of the most important challenges for covalent organic frameworks (COFs) is achieving precise atomic-level structural determination. So far, one-dimensional (1D) porous COFs remain structurally enigmatic owing to anisotropic growth dynamics and limited long-range order. Here we develop a general and systematic protocol to grow high-quality 1D COF crystals. The crystalline architectures of six 1D COFs with high porosity are unambiguously resolved via continuous rotation electron diffraction, with a high resolution of up to 0.90 Å, and all the non-hydrogen atoms can be directly located. The crystal structures reveal the structural details of these 1D COFs with different functional groups, including interchain interactions, stacking mode, interlayer distance, interlayer slip and interchain spacing. We also find that introducing steric methyl groups to disrupt interlayer stacking can transform COF structures from AA stacking into AB stacking. Finally, the COF crystals can undergo a crystal-to-crystal transformation by reducing the imine to amine linkage, resulting in enhanced chemical stability, hydrophobicity and proton conductivity.