Rational Molecular Doping of Carbon Nitride With Bis(diaminotriazinyl)‐Substituted Pyridine: Creating Ligand‐Like Cu Coordination Sites for Enhanced Photocatalytic H 2 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 Cu 2+ ‐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.