Donor to Acceptor Charge Transfer in Carbazole-based Conjugated Microporous Polymers for Enhanced Visible-Light-Driven Photocatalytic Water Splitting

Nowadays, conjugated microporous polymers (CMPs) of the donor-acceptor (D-A) type show excellent photocatalytic performance in water splitting due to their efficient isolation of light-induced excitons. The key to this activity lies in the appropriate selection of electron donor and acceptor units. In this paper, we synthesized three D-A carbazole-based CMPs and investigated the influence of planarity, electronic structure, crystallinity, and surface area on their photocatalytic efficiency in hydrogen evolution from water. Our CMPs have excellent light collection ability, fast separation rates, and minimal recombination rates for the electron/hole pairs, so an excellent hydrogen evolution rate (HER) was achieved by water reduction. Moreover, the most efficient semiconductor Cz-4Py CMP, which had the lowest dihedral angle, more suitable LUMO level, semi-crystalline nature, and largest surface area, showed the best HER up to 8813 μmol g⁻¹ h⁻¹ under visible light with an apparent quantum yield (AQY) of 4.51 % at λ=420 nm. While the HERs for Cz-4TPT and Cz-4TzTz CMPs with higher dihedral angle, amorphous nature, and lower surface area were 1702 and 1541 μmol g⁻¹ h⁻¹, respectively. The efficiencies obtained exceed those of many polymeric materials reported for photocatalytic H₂O reduction. This work confirms the importance of the molecular design of CMP photocatalysts to optimize their performance in hydrogen release by water dissociation.