Electrochemiluminescent dinuclear Ru(II) complexes assembled with 1,1′-(1,2-ethynediyl)- or dimethlyene-bridged bis(bipyridine) ligands: Synthesis and photophysical and electrochemical properties

1,2-Di(2,2′-bipyridin-5-yl)ethane (BL1) and 1,2-di(2,2′-bipyridin-5-yl)ethyne (BL2) were synthesized as new bridging ligands and coordinated to (RuL2(acetone)2)(PF6)2 for the preparation of various [Ru(L)2(BL)Ru(L)2](PF6)4-type dinuclear ruthenium complexes (where BL = BL1, BL2 and L = bpy, o-phen, DTDP). The electrochemical redox potentials, spectroscopic properties, and relative electrochemiluminescence intensity of BL1 and BL2 were characterized and compared to those of well-known tris(1,10-phenanthroline)rutheniun(II) [Ru(o-phen)3](PF6)2] complex as a reference. Dinuclear Ru(II) complexes containing the conjugated bridging ligand (BL2) showed much more intense electrochemiluminescent responses than dinuclear Ru(II) complexes with the non-conjugated bridging ligand (BL1). Among the complexes with conjugated bridging ligands, [(DTDP)2Ru(bpy-CC-bpy)Ru(DTDP)2](PF6)4 exhibited enhanced ECL intensities as high as 3.6 times greater than that of the reference, [Ru(o-phen)3](PF6)2.