Sub-Stoichiometric Covalent Organic Frameworks

Covalent organic frameworks (COFs) have garnered significant attention for nearly two decades due to their exceptional structural designs, tunable properties, and wide-ranging applications. Recently, a novel subclass of COFs known as partially condensed, sub-stoichiometric COFs (ss-COFs) has emerged. This presents a promising new avenue for constructing distinct COF structures in contrast to fully condensed, stoichiometric COFs (fc-COFs). ss-COFs are deliberately designed with periodic unreacted functional groups, thereby giving rise to intriguing electronic, optical, and catalytic properties. The deviation from conventional stoichiometric approach opens up new prospects to tailor material properties for unexplored applications. Here, this review focuses on the latest advancements and breakthroughs in ss-COFs, including topological design, structure characterization, synthetic method, and practical applications. From their basic designing principles to cutting-edge properties, it will be explored how ss-COFs are paving the way for COFs research and pushing the boundaries toward new scientific and technological possibilities. © 2024 Wiley-VCH GmbH.