Molecular engineering in thizolo[5,4-d]thiazole-based donor-acceptor covalent organic framework Induced high-efficient photosynthesis of H₂O₂

Covalent organic frameworks (COFs), as a newly emerging kind of porous and crystalline materials, serve as an ideal template for hydrogen peroxide (H₂O₂) photosynthesis. However, the vision of achieving high efficiency and selectivity in H₂O₂ photosynthesis is greatly hindered by the large exciton binding energy and limited charge separation efficiency influenced by the molecular structure of the building blocks. Herein, we developed three newly designed COFs with a donor–acceptor (D-A) structure and incorporated regulatory units (fluorine, F, and methoxyl, OCH₃) in the D-A pathway through molecular engineering to optimize electronic structure, the availability of activate sites, charge kinetics and O₂ activation capacity. Due to electron-donating effect, OCH₃-functionalization (NIES-COF-3) can strengthen the intramolecular electron transfer and interaction with O₂. This results in a reduction of the energy barrier of the rate-determining step (*O₂ → *OOH) and excellent O₂-to-H₂O₂ photocatalytic activity under visible light irradiation, delivering an H₂O₂ production rate of 3238.4 μmol g⁻¹h⁻¹ and a high apparent quantum yield of 3.17 %. In addition, F-functionalization (NIES-COF-2) primarily reduces the band-gap energy and improve the O₂ adsorption capacity compared to unfunctionalized NIES-COF-1. This work unveils insight into the catalytic activity-optimization mechanism of molecular engineering in the D-A structure and provides important references for photocatalysts.