Azobenzene Functionalized Organic Covalent Frameworks: Controlled Morphologies and Photo‐Regulated Adsorption

Abstract Covalent organic frameworks (COFs) containing azobenzene building blocks carry great potential for use in intelligent storage, separation, chemical sensing, and catalysis due to their intriguing photo‐responsiveness. However, azobenzene units are often exploited as the linkers to form the framework of COFs, thereby restricting their molecular motion and photoisomerization. Herein, a simple yet robust template‐free solvothermal strategy is reported to yield azobenzene‐dangled COFs (Azo‐COFs) with their azobenzene moieties suspending within the pores. The crystallinity, specific surface area, and morphology of Azo‐COFs can be conveniently tailored by changing the ratio of amine to aldehyde monomers. Notably, the Azo‐COFs provide sufficient free space for the reversible trans‐to‐cis isomerization of the dangled azobenzene units inside the pores, thus reversibly regulating surface wettability of Azo‐COFs. The adsorption capacity of Azo‐COFs toward organic dye molecules is increased by 3.7‐fold when irradiated with ultraviolet light, which can be ascribed to the intelligent closing/opening of molecular gates rendered by photoisomerization of azobenzene moieties. As such, the ability to photoregulate the adsorption of Azo‐COFs highlights their significance in functioning as smart porous nanomaterials for applications in cargo release, molecular sieves, ion transport, energy conversion systems, and environmental remediation.