Molecular Triazine–Heptazine Junctions Promoting Exciton Dissociation for Overall Water Splitting with Visible Light

The Frenkel exciton dissociation efficiency and the subsequent free charge carrier migration rate mainly determine the photocatalytic property of polymeric carbon nitride (PCN). Herein, by postcalcination of heptazine-based PCN in molten salts at mild temperature (673 K), we are able to design a series of crystalline PCNs with a promising triazine–heptazine hybrid structure. The molecular triazine–heptazine junctions promote the exciton splitting, while the ordered in-plane packing structure facilitates the hot charge carrier migration. Accordingly, the optimal triazine–heptazine-based PCN exhibits a dramatically enhanced activity toward one-step excitation photocatalytic overall water splitting to generate H₂ and O₂ with visible light over heptazine-based pristine PCN, by a factor of ∼34 times.