Intramolecular Charge Transfer and Extended Conjugate Effect in Donor-π-acceptor Type Mesoporous Carbon Nitride for Synergistically Enhanced Photocatalytic Hydrogen Evolution.

Inspired by D-A polymers in organic solar cell and extended conjugate effect, a conceptual design of D-π-A type mesoporous carbon nitride with benzene or thiophene as π-spacer is proposed as an efficient photocatalyst for hydrogen evolution and successfully synthesized in one-pot thermopolymerization based on nucleophilic substitution and Schiff base chemical reaction. On the molecular level, the inserted in-plane benzene as π-spacer by forming covalent bonds C=N (acceptor) and C-N (donor) interrupts the continuity of 3, s-triazine units while it 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 for electrons, leading to boosted optical absorption capability and enhanced photo-generated carrier separation. With the synergistic effects in mesoporous structure, excellent optical and electronic properties, the H2 evolution rate achieves a fivefold increase compared to that of pristine g-C3N4 with robust performance. In addition, other simple aromatic heterocyclic compounds (i.e. pyridine, thiophene and furan) based D-π-A structures with higher hydrogen evolution rate (up to sevenfold increase) are also explored to broaden the application in designing novel photocatalysts.