Rational Molecular Doping of Carbon Nitride With Bis(diaminotriazinyl)-Substituted Pyridine: Creating Ligand-Like Cu Coordination Sites for Enhanced Photocatalytic H2 Production.

Graphitic carbon nitride (g-CN) is a potent photocatalyst for photochemical HER, but in its pristine form it suffers from poor carrier transport, rapid recombination, and the absence of defined catalytic sites. Herein, a ligand-inspired molecular doping approach is reported for embedding a terpyridine-like coordination environment directly within the carbon nitride backbone. A bis(diaminotriazinyl)-substituted pyridine derivative (Pyridine-2,6-DAT) was utilized as a dopant due to its diaminotriazine units being polymerizable and compatible with heptazine formation, while its 2,6-substituted-pyridine core preserved a terpyridine-like metal-coordinating site. Pyridine-2,6-DAT preserves a ligand-like nitrogen arrangement post-polymerization, unlike other pyridine-doping approaches that lack geometric control. Copolymerizing Pyridine-2,6-DAT with melamine yielded a ligand-embedded carbon nitride (g-CN_Py), which upon subsequent postmetalation with Cu2+-ions yielded g-CN_Py_Cu. The postmetalation approach greatly facilitated Cu incorporation at the embedded ligand environments while limiting uncontrolled deposition or clustering. The resulting Cu-integrated photocatalyst exhibited substantial improvement in photocatalytic HER activity compared to pristine g-CN, by improving charge separation and utilization and suppressing radiative recombination. Also, this work represents rational molecular doping as an important route to construct catalytically active ligand-directed semiconductor architectures for sustainable photocatalytic hydrogen production by bridging the molecular precision of homogeneous ligand environments with the robustness and scalability of heterogeneous carbon nitride photocatalysts.