Design of Photothermal Covalent Organic Frameworks by Radical Immobilization

Abstract

Covalent organic frameworks (COFs) characterized by structural diversity, face-to-face stacking and open channels exhibit unique advantages as photothermal materials but have rarely been applied in solar-driven water evaporation due to complicated framework design, tedious synthesis, and low solar-to-vapor efficiency. Herein, we report a materials design strategy to produce efficient and robust photothermal COF by anchoring nonemissive radicals to the pore surface by a [2+2] cycloaddition–retroelectrocyclization reaction. The radical COF not only possesses the features of COFs such as crystallinity, porosity, and chemical robustness, but also the characteristics of radicals including high spin density and extended absorption to the near-infrared region, which endow the radical COF with outstanding photothermal properties. The radical COF achieves exceptional temperature increment and good photostability upon irradiation with an 808-nm laser, exhibits solar-to-vapor efficiency up to 90.7%, and is adaptable for efficient seawater desalination. Our results provide a new design strategy for the facile production of COF-based photothermal materials.