Isomeric 2D and 3D covalent organic frameworks induced by inter-modular hydrogen bonds for photocatalytic CO2 reduction

Abstract

The rational adjustment of conformational polymorphism of building blocks is able to generate isomeric extending frameworks with different two- and three-dimensional (2D and 3D) structures, being available but very challenging. Herein, the hydrogen-bonding locking strategy is proposed to tune the molecular conformations of building block for crystallizing 2D and 3D covalent organic frameworks (COFs). Under the same reaction conditions, the imine condensation of N,N,N′,N′-tetrakis(4-aminophenyl)-1,4-phenylenediamine (TAPD) and dihydroxyterephthalaldehyde isomers generates isomeric COFs with 2D kgm and 3D qtz topology, respectively. Their isomeric structures have been disclosed by investigations of powder X-ray diffraction in combination with high resolution transmission electron microscopy. This is due to that the distinct inter-modular hydrogen bonds induce the conformation change of TAPD. Post-metalation of COFs isomers with either catechol or 2-(benzylideneamino)phenol sites are conducted for the photocatalysis of CO₂ reduction. The cobalt-containing COFs show the CO production rate of up to 7575 µmol g⁻¹h⁻¹ and selectivity of 94 %. This work opens a new gate by introducing hydrogen bonding moieties to simultaneously adjust frameworks structures and functionalities.