Covalent organic frameworks (COFs) are crystalline organic frameworks consisting of a network structure made of covalent bonds.^1,2) COFs are classified as porous crystalline materials similar to metal-organic frameworks (MOFs)/porous coordination polymers (PCPs) and zeolites. They include 2D COFs, which are constructed by stacking layers of 2D covalently bonded sheets, and 3D COFs, which are constructed by 3D connected frameworks. COFs are expected to be used as molecular storage or separation materials, catalysts, electronic materials, energy storage materials, battery materials, and drug delivery materials, due to their porosity, crystallinity, and structural diversity.

COFs are designed and synthesized by combining monomers, also called linkers, according to intended topology. TCI has more than 70 linkers in stock, and we are constantly adding new items to our catalog. Common linkers are shown below by functional groups.

Aldehyde Linkers

A type of COFs based on imine linkage, synthesized by condensation of aldehydes and amines, was first reported in 2009,³⁾ and imine-based COFs have become the most widely reported COFs. One of the advantage of imine based COFs is their higher chemical stability compared to boroxines and boronate esters. In addition, a number of researchers have reported post-synthetic modification or functionalization of imine based COFs, e.g., COFs for CO₂ capture were synthesized by post-synthetic modification and functionalization of imine-based structures.⁴⁾ In 2012, β-ketoenamine-type COFs synthesized by using 2,4,6-triformylphloroglucinol (TPG, TFP) as an aldehyde linker were reported,⁵⁾ and have recently attracted much attention because of their stability towards acids and bases.

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Amine Linkers

Amine linkers are used to synthesize imine-linked COFs by condensation of aldehydes and amines as described in the aldehyde linkers section, as well as imide-linked COFs mentioned in the carboxylic anhydride linkers section below, and squaraine-linked COFs.⁶⁾

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Carboxylic Anhydride Linkers

Imide-linked COFs obtained by condensation of carboxylic anhydrides and amines have also been reported⁷⁾ and are expected to be applied to battery materials⁸⁾ and CO₂ capture materials.⁹⁾

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Boronic Acid Linkers

The self-condensation of boronic acids to produce boroxines and the condensation of boronic acids and catechols to produce boronic esters are the first synthetic strategies to synthesize COFs.¹⁰⁾

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Other Linkers

COFs can also be constructed with linkers beyond imines, imides, and boroxines. COFs prepared using linkers other than amines, aldehydes, carboxylic anhydrides, and boronic acids could include those utilizing hydrazones, azines, C=C double bonds, etc.
For example:

1. Hydrazone-type COFs synthesized with hydrazides and aldehydes, are known for their structural flexibility and significant potential for post-synthetic modifications.^11,12,13)
2. Ionic COFs synthesized using 1,2,3-triaminoguanidinium chloride, where the triaminoguanidinium cation reacts with an aromatic aldehyde to form the covalent linkages within the framework.¹⁴⁾
3. β-ketoenamine-type COFs can also be derived by synthesizing precursors with urea linkage. After the precursor with highly-reversible urea linkages is formed, the "reconstruction" process transforms it into the final β-ketoenamine COF. Researchers can achieve a significantly higher crystallinity and surface area in the final β-ketoenamine COF by using this "precursor approach" with urea linkages.¹⁵⁾

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Related Products

The following is a list of common reagents that are used as modulators to increase the crystallinity of the resulting COFs and as catalysts for the synthesis of COFs.

Modulators

Catalysts

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Examples of COFs Synthesis

Synthesis of COF-300 ³⁾

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Synthesis of TpPa-1 ⁵⁾

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Synthesis of COF-1 ¹⁰⁾

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Synthesis of Bth-Dma COF ¹³⁾

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Synthesis of RC-COF-3 ¹⁵⁾

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Related Product Category Pages

• Covalent Organic Frameworks (COFs) Linkers

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Product Brochures

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References

• 1) Covalent Organic Frameworks: Organic Chemistry Extended into Two and Three Dimensions
  • S. J. Lyle, P. J. Waller, O. M. Yaghi, Trends Sci. 2019, 1, 172.
• 2) Covalent Organic Frameworks: Structures, Synthesis, and Applications
  • M. S. Lohse, T. Bein, Adv. Funct. Mater. 2018, 28, 1705553.
• 3) A Crystalline Imine-Linked 3-D Porous Covalent Organic Framework
  • F. J. Uribe-Romo, J. R. Hunt, H. Furukawa, C. Klöck, M. O’Keeffe, O. M. Yaghi, J. Am. Chem. Soc. 2009, 131, 4570.
• 4) Covalent Organic Frameworks for Carbon Dioxide Capture from Air
  • H. Lyu, H. Li, N. Hanikel, K. Wang, O. M. Yaghi, J. Am. Chem. Soc. 2022, 144, 12989.
• 5) Construction of Crystalline 2D Covalent Organic Frameworks with Remarkable Chemical (Acid/Base) Stability via a Combined Reversible and Irreversible Route
  • S. Kandambeth, A. Mallick, B. Lukose, M. V. Mane, T. Heine, R. Banerjee, J. Am. Chem. Soc. 2012, 134, 19524.
• 6) A Squaraine-Linked Mesoporous Covalent Organic Framework
  • A. Nagai, X. Chen, X. Feng, X. Ding, Z. Guo, D. Jiang, Angew. Chem. Int. Ed. 2013, 52, 3770.
• 7) Designed synthesis of large-pore crystalline polyimide covalent organic frameworks
  • Q. Fang, Z. Zhuang, S. Gu, R. B. Kaspar, J. Zheng, J. Wang, S. Qiu, Y. Yan, Nat. Commun. 2014, 5, 4503.
• 8) Covalent Organic Framework with Highly Accessible Carbonyls and π-Cation Effect for Advanced Potassium-Ion Batteries
  • X.-X. Luo, W.-H. Li, H.-J. Liang, H.-X. Zhang, K.-D. Du, X.-T. Wang, X.-F. Liu, J.-P. Zhang, X.-L. Wu, Angew. Chem. Int. Ed. 2022, 61, e202117661.
• 9) Synthesis, characterization, and CO2 uptake of mellitic triimide-based covalent organic frameworks
  • H. Veldhuizen, A. Vasileiadis, M. Wagemaker, T. Mahon, D. P. Mainali, L. Zong, S. van der Zwaag, A. Nagai, J. Polym. Sci. Part A: Polym. Chem. 2019, 57, 2373.
• 10) Porous, Crystalline, Covalent Organic Frameworks
  • A. P. Côté, A. I. Benin, N. W. Ockwig, A. J. Matzger, M. O’Keeffe, O. M. Yaghi, Science 2005, 310, 1166.
• 11) Crystalline Covalent Organic Frameworks with Hydrazone Linkages
  • F. J. Uribe-Romo, C. J. Doonan, H. Furukawa, K. Oisaki, O. M. Yaghi, J. Am. Chem. Soc. 2011, 133, 11478.
• 12) Hydrazone-Linked Covalent Organic Frameworks
  • H. Zhuang, C. Guo, J. Huang, L. Wang, Z. Zheng, H.-N. Wang, Y. Chen, Y.-Q. Lan, Angew. Chem. Int. Ed. 2024, 63, e202404941.
• 13) Stable Hydrazone-Linked Covalent Organic Frameworks Containing O,N,O'-Chelating Sites for Fe(III) Detection in Water
  • G. Chen, H.-H. Lan, S.-L. Cai, B. Sun, X.-L. Li, Z.-H. He, S.-R. Zheng, J. Fan, Y. Liu, W.-G. Zhang, ACS Appl. Mater. Interfaces 2019, 11, 12830.
• 14) Cationic Covalent Organic Framework Nanosheets for Fast Li-Ion Conduction
  • H. Chen, H. Tu, C. Hu, Y. Liu, D. Dong, Y. Sun, Y. Dai, S. Wang, H. Qian, Z. Lin, L. Chen, J. Am. Chem. Soc. 2018, 140, 896.
• 15) Reconstructed covalent organic frameworks
  • W. Zhang, L. Chen, S. Dai, C. Zhao, C. Ma, L. Wei, M. Zhu, S. Y. Chong, H. Yang, L. Liu, Y. Bai, M. Yu, Y. Xu, X.-W. Zhu, Q. Zhu, S. An, R. S. Sprick, M. A. Little, X. Wu, S. Jiang, Y. Wu, Y.-B. Zhang, H. Tian, W.-H. Zhu, A. I. Cooper, Nature 2022, 604, 72.

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