Donor Optimization Engineering in Triazine–Based D–π–A Conjugated Polymers: Enhancing Spatial Charge Separation for Efficient Photocatalytic H2O2 Generation

The photocatalytic two–electron oxygen reduction reaction (2e - ORR) for hydrogen peroxide (H 2 O 2 ) production offers a green and sustainable alternative to the energy–intensive anthraquinone process. Donor–π–acceptor (D–π–A) conjugated polymer photocatalysts are suitable for this reaction because their electronic structures and visible–light absorption can be readily tuned. However, inefficient charge separation and limited ORR selectivity remain major challenges. Here, we regulate the donor unit in a D–π–A polymer comprising an alkynyl triazine acceptor and an alkynyl π–bridge by replacing the fluorenone (DBF) donor with thienothiophene (DBTT). The stronger electron–donating character of DBTT promotes spatial separation of the highest occupied and lowest unoccupied molecular orbitals, facilitating charge separation and suppressing carrier recombination. Consequently, TEPT–DBTT achieves an H 2 O 2 production rate of 2273 μmol g -1 h -1 under visible light, approximately six times higher than that of TEPT–DBF. This study demonstrates that donor–unit engineering effectively modulates spatial charge separation and enhances photocatalytic H 2 O 2 production, providing a molecular design strategy for efficient triazine–based D–π–A polymer photocatalysts.