Flipping the Molecular Light Switch Off:  Formation of DNA-Bound Heterobimetallic Complexes Using Ru(bpy)₂tpphz²⁺ and Transition Metal Ions

Formation of a DNA-bound heterobimetallic complex involving Ru(bpy)2tpphz2+ (tpphz = tetrapyrido[3,2-a:2‘,3‘-c:3‘ ‘,2‘ ‘-h:2‘ ‘,3‘ ‘-j]phenazine) and Cu2+ is proposed. The monomeric Ru(bpy)2tpphz2+ is highly luminescent in B-DNA at [DNA-P]/[Ru] = 50, 10 μM Ru. Upon addition of Cu2+, luminescence loss and spectral shifts consistent with Cu2+ complexation and strong associational quenching are observed. Formation of a Ru(bpy)2tpphz2+/Cu2+ DNA complex which places one metal center in the major groove and the other in the minor groove on the opposing side of the helical axis is proposed.