Abstract
Proton conduction pathways and mechanisms in covalent organic frameworks (COFs) have long been obscured by polycrystalline disorder. Here we report a solvent-free melt-phase post-synthetic modification (PSM) strategy that enables precise functionalization of three-dimensional single-crystalline COFs while preserving crystallinity. This methodology overcomes the limitations of solvent-mediated PSM by operating above the melting point of azole reagents, ensuring homogeneous pore accessibility without solvent occlusion. Applied to archetypal imine-linked COF-300, the method achieves crystallographically resolved conversion of fragile imine bonds (C = N, 1.245 Å) into robust amine linkages (C–N, 1.415 Å), concurrently covalently anchoring of proton-conductive azoles (C–N, 1.487 Å) on the COFs skeleton. The resulting azole-functionalized COFs (COF-300-1,2,3-triazole, COF-300-1,2,4-triazole, COF-300-pyrazole) exhibit intrinsic anhydrous superprotonic conductivity reaching 4.35 × 10−3 S cm−1 at 170 °C, with low activation energies (0.153–0.186 eV). Atomic-resolution crystallography and DFT calculations reveal that rigid hydrogen-bond networks eliminate thermal barriers for proton hopping, establishing a definitive structure-property correlation for proton transport in single-crystal COFs. This work pioneers a versatile platform for functionalizing 3D crystalline porous materials under solvent-free conditions.
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Data availability
The X-ray crystallographic coordinates for structures reported in this article have been deposited at the Cambridge Crystallographic Data Center (CCDC), under deposition numbers CCDC 2418811 (COF-300-1,2,3-triazole), 2468192 (COF-300-1,2,4-triazole), 2468193 (COF-300-pyrazole), 2468194 (imidazole@COF-300), 2468195 (2-Methylimidazole@COF-300), 2468196 (2-Ethylimidazole@COF-300), 2468197 (benzimidazole@COF-300), 2468198 (benzotriazole@COF-300). These data can be obtained free of charge from the CCDC via www.ccdc.cam.ac.uk/data_request/cif. The data generated in this study are provided in Supplementary Information and Source Data file. All data are available from the corresponding author upon request. Source data are provided in this paper. Source data are provided with this paper.
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Acknowledgements
This work was financially supported by the National Natural Science Foundation of China (no. 22371032).
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X.W. and C.S. conceived the idea. A.Y. conducted the synthesis and crystal growth of COF-300 and postsynthetic modifications. J.L. conducted the addition reaction mechanism. C.Z., and H.X. conducted the theoretical calculation. K.S. and C.Q. carried out the crystallographic studies. A. Y. and H. Z. and conducted the impedance spectroscopy measurements. X.W., Z.S., and D.J. interpreted the results and wrote the manuscript.
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Yao, A., Zhu, C., Liu, J. et al. Enhanced proton conductivity in azole-functionalized three-dimensional crystalline covalent organic frameworks. Nat Commun (2026). https://doi.org/10.1038/s41467-025-67873-4
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DOI: https://doi.org/10.1038/s41467-025-67873-4
