Azine-linked covalent organic frameworks: recent developments in synthesis and functional applications

Covalent organic frameworks (COFs) have emerged as a unique class of crystalline porous materials assembled from light elements <i>via</i> dynamic covalent linkages, offering exceptional tunability, stability, and functionality. Among various COF linkages, azine-linked COFs, derived from Schiff-base condensation between aldehydes and hydrazine derivatives, have gained significant consideration owing to their enhanced chemical robustness, π-conjugation, and hydrolytic stability compared to conventional imine-based COFs. Additionally, azine linked COFs possess well-ordered pore structure, high porosity, good crystallinity, large accessible surface area, and tunable pore chemistry. These attributes make them promising candidates for various applications such as CO₂ capture, hydrogen evolution, organic transformations, and removal of pollutants or ions even at high temperatures. This review highlights the recent advancements in the design strategies, synthetic methods, and structural features of azine-linked COFs, along with their emerging applications in CO₂ capture, hydrogen evolution, organic transformations, and pollutant degradation. In addition, a brief overview of general COF linkages and synthetic approaches is provided to establish a broader context. Finally, current limitations and future perspectives are investigated to guide the continued development of Schiff-base-derived azine linkage COFs as versatile platforms for sustainable functional materials.