Synthesis, photophysical, and electrochemical properties of six Ru(II) complexes: asymmetric ligands composed of 6-phenyl substituted 2,2′-bipyridine and 4,5-diazafluorene derivatives

<p>Six asymmetric ligands, 6-[(4,5-diazafluoren-9-ylimino)methyoxyphenyl]-2,2′-bipyridine (L<sup>1</sup>), 4-[(4,5-diazafluoren-9-ylimino)methyoxyphenyl]-6-phenyl-2,2′-bipyridine (L<sup>2</sup>), 6-[4-(4,5-diazafluoren-9-ylimino)phenoxybenzyl]-2,2′-bipyridine (L<sup>3</sup>), 4-[4-(4,5-diazafluoren-9-ylimino)phenoxybenzyl]-6-phenyl-2,2′-bipyridine (L<sup>4</sup>), 6-[2-(4,5-diazafluoren-9-ylimino)phenoxybenzyl]-2,2′-bipyridine (L<sup>5</sup>) and 4-[2-(4,5-diazafluoren-9-ylimino)phenoxybenzyl]-6-phenyl-2,2′-bipyridine (L<sup>6</sup>), and corresponding Ru(II) complexes [(bpy)<sub>2</sub>Ru(L<sup>1–6</sup>)](PF<sub>6</sub>)<sub>2</sub> (bpy = 2,2′-bipyridine) were synthesized. All six ligands have two kinds of nonequivalent chelating sites: one involving the 6-phenyl substituted 2,2′-bipyridine moiety, and the other involving the 4,5-diazafluorene moiety. All six Ru(II) complexes have metal-to-ligand charge transfer absorptions around 447 nm and one Ru(II)-centered oxidation around 1.35 V <i>versus</i> SCE in CH<sub>3</sub>CN solution at room temperature. These complexes are non-emissive in CH<sub>3</sub>CN solution at room temperature. The emission intensities of [(bpy)<sub>2</sub>Ru(L<sup>1</sup>)]<sup>2+</sup> and [(bpy)<sub>2</sub>Ru(L<sup>2</sup>)]<sup>2+</sup> are stronger than that of [(bpy)<sub>2</sub>Ru(L<sup>3–6</sup>)]<sup>2+</sup> in EtOH-MeOH (4 : 1, v/v) glassy matrix at 77 K.</p>