Synthesis and characterization of a series of transition metal polypyridyl complexes and the pH-induced luminescence switch of Zn(II) and Ru(II) complexes

► Synthesis five transition metal complexes with imidazole rings. ► The Zn(II) and Ru(II) complexes show proton-dependent photophysical properties. ► The two complexes act as pH-induced “off-on-off” luminescence switches.