Porous organic cages (POCs) are constructed from purely organic synthons by covalent linkages with intrinsic cavities and have shown potential applications in many areas. However, the majority of POC synthesis methods reported thus far have relied on dynamically reversible imine linkages, which can be metastable and unstable under humid or harsh chemical conditions. This instability significantly hampers their research prospects and practical applications. Consequently, strategies to enhance the chemical stability of POCs by modifying imine bonds and developing robust covalent linkages are imperative for realizing the full potential of these materials.

The stability (e.g., thermal, mechanical, hydrolytic, chemical, or photolytic stability) of materials is fundamental, and chemical stability is one of the most important characteristics of POCs which is deeply influenced by chemical bonds. Thus, there is a growing demand for methods in constructing chemically stable POCs to advance the development of porous materials across various fields. However, few reviews have been conducted on this topic.

In a study published in Chem. Commun., the research group led by Prof. YUAN Daqiang from Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, provided a comprehensive overview of recent advancements in the development and application of stable POCs.

From the perspective of chemical bonds, it offers two strategies for preparing stable POCs: modifying imine linkages to increase the POCs’ stability; using robust covalent linkages to prepare stable POCs. As for the former, to date, the proposed strategies for increasing the stability of imine linkage can be divided into three fundamentally different categories. As for the latter, stable POCs constructed from more robust linkages based on alkyne metathesis, imide formation, nucleophilic aromatic reactions, Knoevenagel reaction, and so on have been recently achieved. It highlights selected significant reports on the efficient synthesis of stable POCs utilizing these strategies. Moreover, an outlook on future suggestions for efficient synthesis of stable POCs, along with the future opportunities that require attention, has also been presented.

Besides, researchers also presented three critical perspectives on synthesizing stable POCs and their advanced applications. Cyclization of imines into imidazole, oxazole, thiazole, indazole, as well as asymmetric addition, multicomponent reactions, and linkage exchange methods. Careful consideration must be given to the shape of the organic synthons used in bond-forming reactions. To broaden POCs practical applications across energy, environment, sensors, catalysis, and other fields, functional groups like benzothiadiazole, phthalocyanine, porphyrin, azobenzene, viologen, triazine, and bipyridine can be incorporated into the stable skeletons of POCs.

This study summarizes recent progress in synthesizing stable POCs with enhanced stability and robust covalent linkages.

Selected stable POCs based on Schiff base reactions and other coupling reactions. (Image by Prof. YUAN’s group)

Contact:

Prof. YUAN Daqiang

Fujian Institute of Research on the Structure of Matter

Chinese Academy of Sciences

Email: ydq@fjirsm.ac.cn