Linkage transformation in covalent organic frameworks from dynamic precursors to robust skeletons

Covalent organic frameworks (COFs) derive their structural precision and porosity from the covalent reticulation of organic building units, yet the direct synthesis of highly crystalline frameworks with robust linkages remains a fundamental challenge. Although reversible bonds such as imines enable error correction during crystallization, the formation of chemically robust linkages is often governed by less reversible reactions that limit long-range ordering. This mismatch between crystallization and formation of robust linkages defines a central synthetic challenge in COF chemistry. Linkage transformation offers a powerful solution by decoupling the generation of long-range order from the installation of robust backbone linkages. In this review, we summarize recent advances in linkage transformation strategies that enable access to robust, structurally well-defined, and in some cases single-crystalline COFs that are difficult or inaccessible by direct synthesis. We discuss dynamic bond exchange, dynamic-to-robust backbone conversion, and chemical reconstruction via monomer release and repolymerization, with emphasis on their synthetic logic, mechanistic features, and structural consequences. We further highlight how these transformations preserve, reorganize, or enhance structural order while reshaping topology, morphology, and pore environments. Finally, we outline emerging opportunities and unresolved challenges in leveraging linkage transformation for the rational synthesis of advanced COFs.