Expanding the horizons of covalent organic frameworks: sub-stoichiometric synthesis as an emerging toolkit for functional COFs

Abstract

Covalent organic frameworks (COFs) are a class of porous materials generated from organic molecules resulting in two-dimensional (2D) or three-dimensional (3D) networks. Multifunctional molecules with defined symmetry react to give all-linked-COFs with pre-determined topologies. COFs and COF-based materials have continuously evolved via the exploration of new linkages, synthesis, and processing methodologies over nearly two decades. Several studies have contributed to the understanding of the formation mechanism and the influence of solvent(s), catalysts, and the reaction environment in the crystallization process. Apart from all-linked COFs with a “fully formed” network, sub-stoichiometric synthesis has been a recent development, where the change in stoichiometry of monomers results in generating unconventional topologies along with active functional groups within the pores of these materials. Thus, the generation and utilization of these “functional” COFs is an interesting challenge for reticular chemists, particularly in terms of the vast possibilities of applications that are not likely to emerge from conventional synthesis.