Manipulating Grain Boundary Defects in π‐Conjugated Covalent Organic Frameworks Enabling Intrinsic Radical Generation for Photothermal Conversion

Defects are prevalent in covalent organic frameworks (COFs) constructed based on reversible covalent chemistries. However, manipulating defects in COFs to achieve functionalities remains a significant challenge. Herein, a facial method is provided to regulate the boundary unreacted defects in π‐conjugated COFs to generate distinct and stable paramagnetic radicals, which endow the COFs with a bulk ferromagnetic transition behavior at low temperature, and the efficient photothermal conversion with application in solar vapor generation and seawater desalination. This work not only provides new insights to tailor and control the physicochemical properties of COFs by defect engineering but also enriches the applications of COFs in solar energy utilization.