pH- and DNA-induced dual molecular light switches based on a novel ruthenium(II) complex

A novel Ru(II) complex, [Ru(bpy)2(btppz)]Cl2, where bpy = 2,2′-bipyridine and btppz = benzo[h]tripyrido[3,2-a:2′,3′-c:2″,3″-j]phenazine, has been synthesized and characterized. The pH effects on UV–visible (UV–vis) absorption and emission spectra of the complex have been studied and ground- and excited-state ionization constants of the complex have been derived. The calf thymus DNA (ct-DNA) binding properties of the complex were investigated with UV–vis absorption and luminescence spectrophotometric titrations, steady-state emission quenching by [Fe(CN)6]4−, DNA competitive binding with ethidium bromide, DNA melting experiments, reverse salt titrations and viscosity measurements. The complex was demonstrated to act as dual molecular switches: pH-induced “on–off” emission switch with an on–off intensity ratio of ∼54 which is favorably compared with those reported for structurally analogous Ru(II) complexes, and a DNA molecular light switch with a luminescence enhancement factor of 22 as it intercalatively bound to the DNA.