Versatile Metal-Free Photocatalysts Based on 3D Covalent Organic Frameworks Capable of Reductive and Oxidative Organic Transformations and Polymerizations

There is a need for versatile and effective organic photocatalysts to enable a variety of chemical transformations under mild reaction conditions, and covalent organic frameworks (COFs) are promising crystalline, porous, and sustainable materials for use as heterogeneous photocatalysts. However, prior work with COF photocatalysts has focused primarily on two-dimensional rather than three-dimensional (3D) COF photocatalysts and has not demonstrated the catalysis of both oxidative and reductive transformations. In this work, we investigate the photocatalytic properties of two photoactive 3D COFs. We show that these COFs have broad light absorption and a strong photocurrent response and are effective heterogeneous catalysts for both oxidative and reductive processes, including debromination, chain-growth polymerizations, thiol-ene click reactions, and thiol-ene step-growth polymerizations. Density functional theory calculations demonstrate that these COFs possess strong donor–acceptor and charge carrier separation properties and have appropriate energy level alignments for debromination and thiol oxidation reactions. This work demonstrates the enormous potential of photoactive 3D COFs as both reductive and oxidative photocatalysts.