Photo-Active Covalent Organic Frameworks (COFs) for Photochemical Transformations and Environmental Remediation

Fully Conjugated Covalent Organic Frameworks (COFs) are porous, crystalline, all-organic materials with unique photochemical properties. In this work, we demonstrate that photoactive COFs are effective heterogeneous photocatalysts for organic transformations. First, we investigate the photochemical properties of two-dimensional COFs with a donor-acceptor backbone electronic structure containing porphyrin and tetra-biphenyl repeat units. These COFs are crystalline and porous, with a total accessible surface area exceeding 440 m²/g. The COFs additionally exhibit broad absorption spectra spanning from visible to UV-light and can be used as heterogeneous photocatalysts for photoinduced electron transfer-reversible addition-fragmentation chain transfer (PET-RAFT). We found that the photo-active COFs produced well-defined polymeric products with excitation under blue, green and red light sources and at room temperature. The COFs were also effective photocatalysts in aqueous and organic media. Next, we design three-dimensional conjugated COFs containing trigonal planar and square planar pi-conjugated building blocks. We explore one 3D COF system containing a pyrene photoactive unit as a heterogeneous photocatalyst for reductive and oxidative reactions, including debromination reactions, chain-growth polymerization of styrene, acrylates, and methacrylates, and photo-oxidative thiol-ene click reactions. Finally, in the last part of the presentation, I demonstrate how photoactive COFs can be used for environmental remediation taking advantage of their high accessible pore volumes for adsorption and photochemical properties for degradation. We showt hat 2D COFs adsorb and photochemical degrade perfluoroalkyl substances. These studies demonstrate the unique photophysical properties of conjugated COFs and their versatile applications.