Progress in Azobenzene Porous Organic Polymers: Innovative Structure Evolutions and Applications

Porous polymers with azobenzene skeleton (Azo-POPs), which possess good chemical stability, high specific surface area, and easy functionalization and modification, have shown great application prospects in a number of fields and attracted much attention. In this review, we firstly sorted out the ways of introducing azobenzene structural elements into porous polymer skeletons in recent years, including the condensation polymerization of polyaminoaromatics and poly(nitroso)aromatics, the oxidative coupling polymerization of polyaminoaromatics, the reductive coupling polymerization of poly(nitroso)aromatics and the coupling polymerization of electron-rich aromatics with polydiazonium salts,etc. It is pointed out that the coupling polymerization of electron-rich aromatic hydrocarbons with polydiazonium salts has mild conditions, high polymerization efficiency and good functional group tolerance. The examples and characteristics of functional Azo-POPs is briefly described. The electron cloud, polar dipole interactions and alkalinity provided by amino or hydroxyl groups in Azo-POPs, can significantly improve the adsorption capacity of porous polymers for metal ions, polar compounds and CO2. Then the paper analyzes and demonstrates the irreversible isomerization of tris(beta-hydroxyazo)benzene structure to tris(beta-keto-hydrazone)cyclohexane structure, and analyzes and summarizes the applications of Azo-POPs in the fields of gas and vapor adsorption and storage, multiphase catalysis, removal of pollutants in water,gas membrane separation and electrochemistry. Finally, the challenges to the development of Azo-POPs are analyzed and pointed out, and the future development direction and prospect of Azo-POPs are discussed in the light of the existing research reports.