Cyclopalladation of a Covalent Organic Framework for Near-Infrared Light-Driven Photocatalytic Hydrogen Peroxide Production

Covalent organic frameworks (COFs) have been extensively developed as photosensitizers for photocatalytic energy conversion over the past decade. However, current COF photocatalysts have yet to demonstrate the capability to harvest near-infrared (NIR) light (above 760 nm), which constitutes approximately 53% of the solar spectrum, for fuel or chemical conversion. In this work, we introduce a novel post-synthetic functionalization strategy for COFs by incorporating a palladacycle directly into the COF backbone, extending the light absorption of an azobenzene-based COF into the NIR region. This approach enables homogeneous, atomically-distributed Pd functionalization with a high loading amount of 12 wt% and without noticeable formation of Pd nanoparticles. The cyclopalladated COF, TpAzo-CPd, was utilized as a catalyst for photocatalytic hydrogen peroxide production under 810 nm illumination. This study represents the first implementation of COFs for NIR photocatalysis and opens the door to Pd-single-site COF catalysts for a wide range of organic transformations.