Near-IR Light-Driven Photocatalytic H₂O₂ Production by Viologen-Based Conjugated Microporous Polymer

Near-infrared (NIR) light-driven photocatalytic H₂O₂ generation represents a promising yet underexplored strategy for sustainable solar energy utilisation, offering key advantages such as low energy consumption, suppression of unwanted side reactions, and a superior penetration depth into the material. Herein, we report a vinylene-linked diquat-conjugated microporous polymer (Bpy-2D), synthesised via acid-catalysed Knoevenagel condensation of Bpy and TFB. The synergistic combination of the electron-deficient viologen moiety and the vinylene linkage affords a narrow optical band gap of 1.16 eV and broad NIR absorption extending to ∼1400 nm. Interestingly, the polymer exhibited an exceptionally high electrical conductivity of 1.8 × 10^{- 2} S m^{- 1} in the pristine state. Under NIR light irradiation using a red LED strip (wavelength range of 620-660 nm), an IR lamp (650 and 850 nm), and a 12-IR LED board (850 nm), Bpy-2D achieved a high H₂O₂ production rate of 3.31, 4.01 and 0.48 mmol g^{- 1} h^{- 1}, respectively, with an overall production rate of 5.73 mmol g^{- 1} h^{- 1} under xenon light irradiation. The polymer retained approximately 87% of its initial activity over four consecutive cycles, establishing viologen-based vinylene-linked CMP as a promising class of metal-free NIR-active photocatalyst for sustainable H₂O₂ production.