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Partitioning the interlayer space of covalent organic frameworks by embedding pseudorotaxanes in their backbones


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.

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Fig. 1: A general strategy for design and construction of self-exfoliated COFs with well-defined layer numbers of covalent linkages.
Fig. 2: Synthesis of macrocycle- and pseudorotaxane-based COFs.
Fig. 3: Characterization of the crystallinity of MCOF-1 and the pseudorotaxane complexation in RCOF-1.
Fig. 4: Exfoliation of RCOF-1 and characterization of its crystallinity.
Fig. 5: AFM study of RCOF-0 and RCOF-1.

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Data availability

X-ray crystallographic data have been deposited at the Cambridge Crystallographic Data Centre ( with CCDC reference numbers 1863696 (single-crystal Cy1-MVPF6), and 2006788 (single-crystal CyHz0-MVPF6). A copy of the data can be obtained free of charge via All other data supporting the findings of this study are available within the paper and its Supplementary Information. Data are also available from the corresponding author upon reasonable request.


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K.P.L. acknowledges NRF-CRP grant “Two-Dimensional Covalent Organic Framework: Synthesis and Applications,” grant number NRF-CRP16-2015-02, funded by National Research Foundation, Prime Minister’s Office, Singapore. We acknowledge the use of the imaging facilities at the Center for BioImaging Sciences. Funding for the K2-IS camera is provided by the Singapore National Research Foundation’s Competitive Research Program (NRF-CRP16-2015-05). We thank S. Xiangyan for the solid-state NMR measurement. We thank C. Hyun and T. J. Shin for the synchrotron-based GIXRD measurements.

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Authors and Affiliations



Under the supervision of K.P.L., X.L. designed and performed most of the experiments, including synthesis and characterization of COFs and their model compounds. X.L., H.-S.X. and Q.G. discussed the manuscript. K.L. performed the AFM measurements. Under the supervision of U.M., S.W.C. performed and analysed the TEM of COFs, and N.J. performed and analysed SAED of COFs. X.Z. analysed the TEM results. H.X. performed the Q-plus AFM measurement. Under the supervision of S.Y.Q., J.Q. performed the DFT theoretical calculations. I.-H.P. resolved the single-crystal structures of the model compounds. X.L. and K.P.L. co-wrote the manuscript.

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Correspondence to Kian Ping Loh.

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Supplementary information

Supplementary Information

Supplementary text, Figs. 1–35

Supplementary Table 1

Supplementary Tables 1–7

Supplementary Data 2

Single-crystal file of Cy1-MVPF6

Supplementary Data 3

Single-crystal file of CyHz0-MVPF6

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Li, X., Xu, HS., Leng, K. et al. Partitioning the interlayer space of covalent organic frameworks by embedding pseudorotaxanes in their backbones. Nat. Chem. 12, 1115–1122 (2020).

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