Department of Chemistry, National University of Singapore, Singapore, Singapore.
Department of Physics, National University of Singapore, Singapore, Singapore.
Nat Chem. 2020 Dec;12(12):1115-1122. doi: 10.1038/s41557-020-00562-5. Epub 2020 Nov 2.
Mono- or few-layer sheets of covalent organic frameworks (COFs) represent an attractive platform of two-dimensional materials that hold promise for tailor-made functionality and pores, through judicious design of the COF building blocks. But although a wide variety of layered COFs have been synthesized, cleaving their interlayer stacking to obtain COF sheets of uniform thickness has remained challenging. Here, we have partitioned the interlayer space in COFs by incorporating pseudorotaxane units into their backbones. Macrocyclic hosts based on crown ethers were embedded into either a ditopic or a tetratopic acylhydrazide building block. Reaction with a tritopic aldehyde linker led to the formation of acylhydrazone-based layered COFs in which one basal plane is composed of either one layer, in the case of the ditopic macrocyclic component, or two adjacent layers covalently held together by its tetratopic counterpart. When a viologen threading unit is introduced, the formation of a host-guest complex facilitates the self-exfoliation of the COFs into crystalline monolayers or bilayers, respectively.
共价有机框架（COFs）的单层或少数层片代表了二维材料的一个有吸引力的平台，通过明智地设计 COF 构建块，可以实现定制的功能和孔。但是，尽管已经合成了各种各样的层状 COF，但要将它们的层间堆叠劈开以获得均匀厚度的 COF 片仍然具有挑战性。在这里，我们通过将类轮烷单元引入其骨架中来分隔 COF 的层间空间。基于冠醚的大环主体被嵌入到双齿或四齿酰腙砌块中。与三齿醛连接子反应生成基于酰腙的层状 COF，其中一个基面由一个层组成，在双齿大环组分的情况下，或者两个相邻的层通过其四齿对应物共价连接在一起。当引入紫精贯穿单元时，主体-客体配合物的形成促进了 COF 分别自剥离成结晶单层或双层。
