pH responsive “off-on-off” luminescent switch of a novel ruthenium(II) complex [Ru(bpy)2(pipipH2)]2+

A novel ruthenium(II) complex [Ru(bpy)2(pipipH2)](ClO4)2 · H2O was found to act as a luminescent pH switch through protonation and deprotonation of the bis-imidazole-containing ligand pipipH2 in aqueous solution at room temperature.