Department of Chemistry , Dartmouth College , 6128 Burke Laboratory , Hanover , New Hampshire 03755 , United States.
Key Laboratory of Green Preparation and Application for Functional Materials, Ministry of Education, School of Materials Science and Engineering , Hubei University , Wuhan 430062 , P.R. China.
J Am Chem Soc. 2019 Jul 10;141(27):10915-10923. doi: 10.1021/jacs.9b05232. Epub 2019 Jun 27.
Covalently linked single-crystalline porous organic materials are highly desired for structure-property analysis; however, periodically polymerizing organic entities into high dimensional networks is challenging. Here, we report a series of topologically divergent single-crystalline hydrogen-bonded cross-linked organic frameworks (HOFs) with visible guest-induced elastic expansions, which mutually integrate high structural order and high flexibility into one framework. These HOFs are synthesized by photo-cross-linking molecular crystals with alkyldithiols of different chain lengths. Their detailed structural information was revealed by single-crystal X-ray analysis and experimental investigations of HOFs and their corresponding single-crystalline analogues. Upon guest adsorption, HOF-2 crystals composed of a 3D self-entangled polymer network undergo anisotropic expansion to more than twice their original size, while the 2D-bilayer HOF-3 crystals exhibit visible, layered sorption bands and form delaminated sheets along the plane of its 2D layers. The dynamic expansion of HOF networks creates guest-induced porosity with over 473% greater volume than their permanent voids, as calculated from their record-breaking aqueous iodine adsorption capacities. Temperature-gated DMSO sorption investigations illustrated that the flexible nature of cross-linkers in HOFs provides positive entropy from the coexistence of multiple conformations to allow for elastic expansion and contraction of the frameworks.
共价键合的单晶多孔有机材料非常适合用于结构-性能分析；然而，将有机单体周期性聚合到高维网络中具有挑战性。在此，我们报道了一系列拓扑不同的单晶氢键交联有机骨架（HOF），具有可见的客体诱导弹性膨胀，将高结构有序性和高柔韧性相互集成到一个骨架中。这些 HOF 通过用光交联具有不同链长的烷二硫醇的分子晶体来合成。通过单晶 X 射线分析和对 HOF 及其相应单晶类似物的实验研究揭示了它们的详细结构信息。在客体吸附时，由 3D 自缠结聚合物网络组成的 HOF-2 晶体经历各向异性膨胀，超过其原始尺寸的两倍，而二维双层 HOF-3 晶体表现出可见的层状吸附带，并沿着其二维层的平面形成分层片。HOF 网络的动态扩展创造了客体诱导的多孔性，其体积比其永久空隙大 473%以上，这是根据其创纪录的水碘吸附容量计算得出的。温度门控 DMSO 吸附研究表明，HOF 中交联剂的柔性本质从多种构象的共存中提供了正熵，从而允许框架的弹性膨胀和收缩。
