Ultrafast Charge Dynamics in Nitrogen-Rich Covalent Organic Frameworks for Hydrogen Peroxide Photosynthesis

Four new tetrazine-based COFs, DT-COF-n (n = 0-3, indicating the number of & horbar;OH groups), incorporating diamino-bis-tetrazine and hydroxy-functionalized benzo-tri-carbaldehyde monomers are used to explore the link between bonding reversibility in supramolecular chemistry and photocatalytic H2O2 production. DT-COFs exhibit an exceptionally high nitrogen content, with 72 nitrogen atoms per pore structure, accounting for 50.3% of the framework composition-far exceeding previously reported COFs with less than 32% nitrogen. This high nitrogen density, coupled with the strong electron-accepting nature of tetrazine units and an azo linker, promotes charge separation and stabilization, critical for efficient photocatalysis. DT-COF-1, which includes a single hydroxyl group, shows a highly ordered structure and extended conjugation. This led to a H2O2 yield of 4300 mu mol g(-1)h(-1) and an apparent quantum yield of 14.1% at 420 nm under visible light in water. With respect to peroxide yield and quantum yield, DT-COF-1 outperforms most other COFs used to produce peroxide. DT-COF-1 also achieves ultrafast intramolecular electron transfer (<500 fs) and a prolonged excited state lifetime (approximate to 90 ps). In situ electron paramagnetic resonance spectroscopy and DFT calculations suggest a Yeager-type absorption of O-2(center dot-) intermediate, favoring H2O2 production.