COFs

Covalent Organic Frameworks (COFs) are crystalline, porous polymers built entirely from light elements connected by strong covalent bonds. They form extended two- or three-dimensional networks through reticular chemistry, enabling precise control over pore size and functionality. COFs are distinguished from metal-organic frameworks by the absence of metal nodes; their frameworks arise solely from organic building blocks linked by covalent bonds such as imine, boronate ester, boroxine, hydrazone, or triazine linkages.

Synthesis and structure: COFs are usually assembled under solvothermal or hydrothermal conditions using dynamic covalent chemistry to allow error-correction and crystallization into extended materials. The choice of linkage geometry and building blocks determines dimensionality and porosity; some COFs are 2D layered materials with pillared stacking, while others are inherently three-dimensional. Crystallinity and stability depend on the linkage type and backbone structure; boron- and boroxine-based COFs can be sensitive to moisture, whereas linkages like β-ketoenamine or certain triazine frameworks offer higher chemical stability.

Properties and applications: COFs exhibit permanent porosity with tunable pore sizes and high surface areas, often exceeding 1000 m2/g. Their properties can be tailored through precursor design and post-synthetic modification. Potential applications include gas storage and separation (for example hydrogen and carbon dioxide), catalysis and photocatalysis, energy storage devices, sensing, and drug delivery. Defect engineering and functionalization enable broader utility and performance optimization.

Development and challenges: Since the first COFs were reported in the 2000s by Omar Yaghi and colleagues, research has expanded link chemistries, crystallinity, and stability, while pursuing scalable synthesis and device integration. Ongoing challenges include achieving robust, defect-controlled crystals suitable for practical applications and ensuring stability under operational conditions.