Near-Infrared Absorbing and Emitting RuII-PtII Heterodimetallic Complexes of Dpdpz (Dpdpz=2,3-Di(2-pyridyl)-5,6-diphenylpyrazine)

The reaction of 2,3-di(2-pyridy1)-5,6-diphenylpyrazine (dpdpz) with K2PtCl4 in a mixture of acetonitrile and water afforded mono-Pt complex (dpdpz)PtCl2 4 in good yield, with two lateral pyridine nitrogen atoms binding to the metal center. Two types of Ru-II-Pt-II heterodimetallic complexes bridged by dpdpz, namely, [(bpy)(2)Ru(dpdpz)Pt(C CC6H4R)(2+) (7-9, R = H, NMe2, or Cl, respectively) and [(tpy)Ru(dpdpz)Pt(C CPh)](+) (12), were then designed and prepared, where bpy = 2,2'-bipyridine and tpy = 2,2';6',2 ''-terpyridine. In both cases, the platinum atom binds to dpdpz with a (CNN)-N-boolean AND-N-boolean AND tridentate mode. However, the coordination of the ruthenium atom with dpdpz could either be noncyclometalated ((NN)-N-boolean AND bidentate) or cyclometalated ((CNN)-N-boolean AND-N-boolean AND tridentate). The electronic properties of these complexes were subsequently studied and compared by spectroscopic and electrochemical analyses and theoretical calculations. These complexes exhibit substantial absorption in the visible to NIR (near-infrared) region because of mixed MLCT (metal-to-ligand-charge-tranfer) transitions from both the ruthenium and the platinum centers. Complexes 7 and 9 were found to emit NIR light with higher quantum yields than those of the mono-Ru complex [(bpy)(2)Ru(dpdpz)](2+) (5) and bis-Ru complex [(bpy)(2)Ru(dpdpz)Ru(bpy)(2)](4+) (13). However, no emission was detected from complex 8 or 12 at room temperature in acetonitrile.