Hydrogen bonding induces dual porous types with microporous and mesoporous covalent organic frameworks based on bicarbazole units

Abstract

Although the topologies of covalent organic frameworks (COFs) can be controlled mainly by varying the symmetries of the building blocks condensed to form the structures, another approach is to change the structures of blocks but retain the same symmetries. The construction of a single COF featuring pores of different sizes from two symmetrical building blocks remains extremely difficult. In this paper, we report an investigation into the effect of hydrogen bonding on the topological regulation of two-dimensional COFs as a new approach for managing their properties. Our strategy involved introducing pristine and substituted diamine monomers—benzidine (BD) and 1,4-dihydroxybenzidine (DHBD)—into the skeleton of bicarbazole-based COFs. The constructed bicarbazole-based COFs, Cz-BD and Cz-DHBD, were designed using a (C 2 + C 2 ) geometry strategy and synthesized through Schiff-base condensations of bicarbazole-4CHO and the benzidine derivatives. The resulting COFs featured two different topologies: Cz-BD COF possessing a single type of pore having a tetragonal structure, and Cz-DHBD COF possessing a Kagome structure featuring two types of pores (one hexagonal and the other triangular with mesoporous and microporous structure, induced by intramolecular OH ⋯ N hydrogen bonding). These COFs exhibited high crystallinity, great thermal stability, and large surface areas, as well as synergistic structural effects and high-performance CO 2 uptake. • Cz-BD COF possessing a single type of pore having a tetragonal structure. • Cz-DHBD COF possessing a Kagome structure featuring two types of pores. • One hexagonal with mesoporous and the other triangular with microporous structure induced by intramolecular hydrogen bonding. • These COFs exhibited high crystallinity, thermal stability, and large surface areas, and high-performance CO 2 uptake.