General Acetal‐Protected Aldehyde Strategy for Facile Synthesis of Covalent Organic Frameworks with Splendid Crystallinity and Uniform Morphology

Crystallinity and morphology are critical factors that closely related to the properties and applications of covalent organic frameworks (COFs). However, the controlled synthesis of COFs with both high crystallinity and uniform morphology remains a significant challenge due to uncontrollable polymerization and complex reaction conditions. In this work, we present a general acetal-protected aldehyde protocol for the facile synthesis of imine-linked COFs, which enables the simultaneous optimization of crystallinity and morphology. Of the acetal-protected aldehydes explored, ethanediol-protected terephthalaldehyde (Tp-E) emerged as the most effective, balancing stability and reactivity to yield highly crystalline Py-COF-E with a well-defined hollow spherical morphology and a significantly enhanced BET surface area compared to its aldehyde-based counterpart Py-COF. This synthetic approach demonstrates broad adaptability across various framework topologies, precursor species, and synthetic solvent systems, simplifying the typically laborious solvent screening process in COF synthesis. Furthermore, Py-DBT-COF-E showed superior photocatalytic H₂ evolution performance relative to Py-DBT-COF, despite their identical chemical compositions, emphasizing the critical role of crystallinity and morphology in determining functional performance. Overall, this study provides a versatile methodology for the controlled synthesis of COFs and offers valuable insights into the interconnected roles of morphology, crystallinity, and material performance.