Metal-Free Covalent Organic Framework for Synergistic Photocatalytic Selective Semi-Dehydrogenation of 1,2,3,4-Tetraisoquinoline and Coproduction of H2O2 in Water.

Selective and green oxidation is a cornerstone of advancing sustainable chemical transformation. Conventional hydrogenation and dehydrogenation typically rely on stoichiometric oxidants or noble metals, operating under harsh conditions. To address these limitations, here, we present an efficient and recyclable photocatalyst: an acetylene-linked triazine-based covalent organic framework (COF) TTB-BTET. The COF was strategically engineered for the selective semidehydrogenation of 1,2,3,4-tetraisoquinolines (THIQs) to 3,4-dihydroisoquinoline (DHIQs), valuable intermediates in pharmaceutical synthesis. Remarkably, the highly crystalline COF exhibits a large surface area, broad visible-light absorption, well-aligned band positions, and functions efficiently in water without the need for an external oxidant, photosensitizer, or metal cocatalyst. It achieves 83% THIQ conversion with 94% selectivity for DHIQ, while simultaneously producing 3.43 mmol g-1 of hydrogen peroxide (H2O2) in 6 h (AQY of 2.89% at λ = 450 nm). Furthermore, DFT calculations confirm that the formation of DHIQ is more favorable over the highly endergonic fully dehydrogenated product. Mechanistic investigation using in situ EPR and in situ DRIFT reveals that this dual functionality originates from the complementary action of singlet oxygen and superoxide and intermediates, along with the simultaneous release of protons during dehydrogenation, collectively driving the in situ generation of H2O2 from molecular oxygen.