Regioselective One‐Step Cyclization and Aromatization towards Directly Amino‐Functionalized Covalent Organic Framework with Stable Benzodiimidazole Linkage

• Published in: Small (Weinheim an der Bergstrasse, Germany) Vol. 19; no. 43; pp. e2303775 - n/a
• Main Authors: Li, Xiaofeng, Jia, Zhimin, Zhang, Jie, Zou, Yingdi, Zhang, Yingdan, Shu, Kewen, Liu, Weijian, Liu, Ning, Li, Yang, Ma, Lijian
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 01.10.2023
• Subjects: amino functionalization; benzodiimidazole linkage; Conjugation; Construction sites; covalent organic frameworks; Crystallinity; Materials science; Nanotechnology; photocatalytic reduction; regioselective reaction; Regioselectivity; Stability; Synthesis; covalent organic frameworks; photocatalytic reduction; benzodiimidazole linkage; regioselective reaction; amino functionalization
• ISSN: 1613-6810; 1613-6829
• DOI: 10.1002/smll.202303775

The compatibility of crystallinity, stability, and functionality in covalent organic frameworks (COFs) is challenging but significant in reticular chemistry and materials science. Herein, it is presented for the first time a strategy to synthesize directly amino‐functionalized COF with stable benzodiimidazole linkage by regioselective one‐step cyclization and aromatization. Bandrowski's base with two types of amino groups is used as a unique monomer, providing not only construction sites for the material framework through specific region‐selective reaction, but also amino active sites for functionality, which is usually difficult to achieve directly in COF synthesis because amino groups are the participants in COF bonding. In addition, the aromatic benzodiimidazole rings and the large conjugated system of the product effectively improve the crystallinity and stability, so that the as‐prepared BBCOF remains unchanged in both acid and base solutions, which is obviously better than the conventional imine‐linked COF. Impressively, the significantly enhanced conjugation degree by the benzodiimidazole structure also endows BBCOF with an efficient photocatalytic reduction of uranyl ion, with removal rate as high as 96.6% in single‐ion system and 95% in multi‐ion system. This study is of great importance to the design and synthesis of functional COFs with a commendable trade‐off among crystallinity, stability, and functionality. A crystalline amino functionalized covalent organic framework (COF) with benzodiimidazole linkage is synthesized using Bandrowski's base that has two types of amino groups with different activities as amino monomer through one‐step regioselective reaction. The benzodiimidazole rings enhance the stability and endow efficient photocatalytic reduction of UO22+ with the removal rate of 96.6%.