The photochemical properties of [Fe CN 6]4- and [Ru bpy 3]2+ differ significantly due to their distinct electronic configurations and coordination geometries.[Fe CN 6]4- complex:In this complex, the central metal ion is Fe II with an electronic configuration of [Ar]3d6. The complex has an octahedral geometry with six cyanide CN- ligands surrounding the Fe II ion. The cyanide ligands are strong-field ligands, which cause a large crystal field splitting in the d-orbitals of Fe II . As a result, the complex has low-energy d-d transitions that are spin-forbidden, making the complex relatively non-emissive and non-photoactive.[Ru bpy 3]2+ complex:In this complex, the central metal ion is Ru II with an electronic configuration of [Kr]4d6. The complex has an octahedral geometry with three bidentate 2,2'-bipyridine bpy ligands surrounding the Ru II ion. The bpy ligands are relatively weaker-field ligands compared to cyanide, leading to a smaller crystal field splitting in the d-orbitals of Ru II . The complex exhibits metal-to-ligand charge transfer MLCT transitions, where an electron is excited from a metal-based d-orbital to a ligand-based * orbital. These MLCT transitions are spin-allowed and have relatively higher energy compared to d-d transitions in [Fe CN 6]4-. As a result, the [Ru bpy 3]2+ complex is highly emissive and photoactive, making it a popular choice for applications in photovoltaics, photocatalysis, and luminescent sensors.In summary, the photochemical properties of [Fe CN 6]4- and [Ru bpy 3]2+ differ due to their distinct electronic configurations and coordination geometries. The [Fe CN 6]4- complex is relatively non-emissive and non-photoactive due to its low-energy, spin-forbidden d-d transitions, while the [Ru bpy 3]2+ complex is highly emissive and photoactive due to its higher-energy, spin-allowed MLCT transitions.