Engineering Heterocyclic Linkages to Expand the Structural and Functional Diversity of Covalent Organic Frameworks

Heterocycle-linked covalent organic frameworks (HC-COFs) are a promising class of crystalline porous polymers constructed by linking organic modules into extended structures via heterocyclic moieties. HC-COFs have received considerable attention due to their robust linkages, extended π-conjugation and abundant heteroatomic sites. These intrinsic characteristics endow HC-COFs with high chemical stability, enhanced light-harvesting ability, and tunable redox activity, thus making them promising systems for widespread applications such as separation, catalysis, sensing, luminescence, biomedicine, energy storage, and environmental remediation. This review aims to provide a comprehensive overview of de novo synthesis and post-synthetic modification strategies employed for the production of HC-COFs, along with their physicochemical properties and representative applications. Finally, we highlight the future opportunities and challenges of HC-COFs for next generation functional materials. This review would offer an insightful understanding of the subtle interplay between heterocyclic linkages and overall skeleton, thus providing a useful guidance on how to further solve the COF trilemma regarding crystallinity, stability and functionality.