Intramolecular Charge Transfer and Extended Conjugate Effects in Donor-π-Acceptor-Type Mesoporous Carbon Nitride for Photocatalytic Hydrogen Evolution.

Inspired by donor-acceptor (D-A) polymers in organic solar cell and the extended conjugation effect, a conceptual design of D-π-A-type mesoporous carbon nitride with benzene or thiophene as a π-spacer is proposed as an efficient photocatalyst for hydrogen evolution. The photocatalyst was successfully synthesized by a one-pot thermopolymerization based on nucleophilic substitution and a Schiff-base chemical reaction. On the molecular level, the insertion of an in-plane benzene as a π-spacer by forming covalent bonds C=N (acceptor) and C-N (donor) interrupts the continuity of tri-s-triazine units and maintains the intrinsic π-π conjugated electronic system. Synchronously, the enlarged electron delocalization and the intramolecular charge transfer induced by polarization provide force-directed migration of electrons, leading to boosted optical absorption capability and enhanced photogenerated carrier separation. With the synergistic effects of the mesoporous structure and excellent optical and electronic properties, a fivefold increase in the H2 evolution rate compared with that of pristine g-C3 N4 was achieved with robust performance. In addition, other simple aromatic heterocyclic compounds (e.g., pyridine, thiophene and furan)-based D-π-A structures with a higher hydrogen evolution rate (up to sevenfold increase) were also explored to broaden the application for the design of novel photocatalysts.