Molecularly Tunable Heterostructured Co-Polymers Containing Electron-Deficient and -Rich Moieties for Visible-Light and Sacrificial-Agent-Free HO Photosynthesis.

As an alternative to hydrogen peroxide (HO) production by complex anthraquinone oxidation process, photosynthesis of HO from water and oxygen without sacrificial agents is highly demanded. Herein, a covalently connected molecular heterostructure is synthesized via sequential C-H arylation and Knoevenagel polymerization reactions for visible-light and sacrificial-agent-free HO synthesis. The subsequent copolymerization of the electron-deficient benzodithiophene-4,8-dione (BTD) and the electron-rich biphenyl (B) and p-phenylenediacetonitrile (CN) not only expands the π-conjugated domain but also increases the molecular dipole moment, which largely promotes the separation and transfer of the photoinduced charge carriers. The optimal heterostructured BTDB-CN manifested an impressive photocatalytic HO production rate of 1920 μmol g h, which is 2.2 and 11.6 times that of BTDB and BTDCN. As revealed by the femtosecond transient absorption (fs-TA) and theoretical calculations, the linkage serves as a channel for the rapid transfer of photogenerated charge carriers, enhancing the photocatalytic efficiency. Further, in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) uncovers that the oxygen reduction reaction occurs through the step one-electron pathway and the mutual conversion between C=O and C-OH with the anchoring of H during the catalysis favored the formation of HO. This work provides a novel perspective for the design of efficient organic photocatalysts.