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 (1) (pipipH2 = 2-(4-(1H-phenanthro[9,10-d]imidazol-2-yl)phenyl)-1H- imidazo[4,5-f][1,10] phenanthroline, bpy = 2,2′-bipyridine) has been found to act as a luminescent pH switch with extraordinary sensitivity through protonation and deprotonation of the bis-imidazole-containing ligand pipipH2 in aqueous solution at room temperature.