A Noble‐Metal‐Free Heterogeneous Photosensitizer‐Relay Catalyst Triad That Catalyzes Water Oxidation under Visible Light

: An entirely earth-abundant chromophore-relay water oxidation catalyst triad system, which is robust and efficient at neutral pH, is presented. The synthesis involves the coordination of a porphyrin derivative to a bridging Fe(CN)5 group, which is then reacted with Co ions to prepare a covalently linked chromophore-Prussian blue analogue assembly. Light-driven water oxidation studies in the presence of an electron scavenger indicate that the triad is active and it maintains a steady activity for at least three hours. Transient absorption experiments and computational studies reveal that the Fe(CN)5 group is more than a linker as it takes part in electron-transfer and co-operates with porphyrin in the charge separation process.