Covalent organic frameworks (COFs) are emerging crystalline porous polymers, showing great potential for applications but lacking gas-triggered flexibility. Atropisomerism was experimentally discovered in 1922 but has rarely been found in crystals with infinite framework structures. Here we report atropisomerism in COF single crystals. The obtained COF atropisomers, namely COF-320 and COF-320-A, have identical chemical and interpenetrated structures but differ in the spatial arrangement of repeating units. In contrast to the rigid COF-320 structure, its atropisomer (COF-320-A) exhibits unconventional gas sorption behaviours with one or more sorption steps in isotherms at different temperatures. Single-crystal structures determined from continuous rotation electron diffraction and in situ powder X-ray diffraction demonstrate that these adsorption steps originate from internal pore expansion with or without changing the crystal space group. COF-320-A recognizes different gases by expanding its internal pores continuously (crystal-to-amorphous transition) or discontinuously (crystal-to-crystal transition) or having mixed transition styles, distinguishing COF-320-A from existing soft/flexible porous crystals. These findings extend atropisomerism from molecules to crystals and propel COFs into the covalently linked soft porous crystal regime, further advancing applications of soft porous crystals in gas sorption, separation and storage.

共价有机框架 (COF) 是新兴的结晶多孔聚合物，显示出巨大的应用潜力，但缺乏气体引发的灵活性。阻转异构现象是在 1922 年通过实验发现的，但在具有无限骨架结构的晶体中很少发现。在这里，我们报告了 COF 单晶中的阻转异构现象。获得的COF阻转异构体，即COF-320和COF-320-A，具有相同的化学和互穿结构，但重复单元的空间排列不同。与刚性 COF-320 结构相反，其阻转异构体 (COF-320-A) 表现出非常规的气体吸附行为，在不同温度下的等温线中具有一个或多个吸附步骤。通过连续旋转电子衍射和原位粉末 X 射线衍射确定的单晶结构表明，这些吸附步骤源自内部孔隙膨胀，有或没有改变晶体空间群。COF-320-A 通过连续（晶体到非晶态转变）或不连续（晶体到晶体转变）或混合过渡方式扩展其内部孔隙来识别不同的气体，将 COF-320-A 与现有的软/柔性多孔材料区分开来晶体。这些发现将阻转异构现象从分子扩展到晶体，并推动 COF 进入共价连接的软多孔晶体状态，进一步推进软多孔晶体在气体吸附、分离和储存中的应用。COF-320-A 通过连续（晶体到非晶态转变）或不连续（晶体到晶体转变）或混合过渡方式扩展其内部孔隙来识别不同的气体，将 COF-320-A 与现有的软/柔性多孔材料区分开来晶体。这些发现将阻转异构现象从分子扩展到晶体，并推动 COF 进入共价连接的软多孔晶体状态，进一步推进软多孔晶体在气体吸附、分离和储存中的应用。COF-320-A 通过连续（晶体到非晶态转变）或不连续（晶体到晶体转变）或混合过渡方式扩展其内部孔隙来识别不同的气体，将 COF-320-A 与现有的软/柔性多孔材料区分开来晶体。这些发现将阻转异构现象从分子扩展到晶体，并推动 COF 进入共价连接的软多孔晶体状态，进一步推进软多孔晶体在气体吸附、分离和储存中的应用。