Direct pore engineering of 2D imine covalent organic frameworks via sub-stoichiometric synthesis

Two-dimensional covalent organic frameworks (2D COFs) bearing various topologies can be precisely designed based on the symmetry of monomers. Their pore environment can be further regulated via either pre-functionalization of the monomers or post-modification of the skeleton. Among them, sub-stoichiometric synthesis is an efficient method which can mediate uncondensed functional moieties periodically arranged in the COF skeletons. Herein, a series of imine-linked 2D COFs with specifically decorated formyl or amino groups were selectively synthesized via sub-stoichiometric formyl transamination. The molar ratios of the monomers directly determine the structures of the resulting COFs with periodic vertex vacancies. The COF with polar amino sites could efficiently capture CO2 and H2O. This work demonstrates tuning the stoichiometry of the monomers could facilely modulate the functions of the pore channels. It also provides insights into constructing novel COFs with complex structures for targeted applications.