Preparation and Photophysical Properties of Bis(tridentate) Iridium(III) Emitters: Pincer Coordination of 2,6-Di(2-pyridyl)phenyl

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The way to prepare molecular emitters [5t + 4t′] of iridium(III) with a 5t ligand derived from the abstraction of the hydrogen atom at position 2 of the aryl group of 1,3-di(2-pyridyl)benzene (dpybH) is shown. In addition, the photophysical properties of the new emitters are compared with those of their counterparts resulting from the deprotonation of 1,3-di(2-pyridyl)-4,6-dimethylbenzene (dpyMebH), at the same position, which are also synthesized. Treatment of 0.5 equiv of the dimer [Ir(μ-Cl)(η 2 -COE) 2 ] 2 (COE = cyclooctene) with 1.0 equiv of Hg(dpyb)Cl leads to the iridium(III) derivative IrCl 2 {κ 3 - N, C, N -(dpyb)}(η 2 -COE) ( 3 ), which reacts with 2-(1 H -imidazol-2-yl)-6-phenylpyridine (HNImpyC 6 H 5 ) and 2-(1 H -benzimidazol-2-yl)-6-phenylpyridine (HNBzimpyC 6 H 5 ) in the presence of Na 2 CO 3 to give Ir{κ 3 - C, N, N -(NImpyC 6 H 4 )}{κ 3 - N, C, N -(dpyb)} ( 4 ) and Ir{κ 3 - C, N, N -(NBzimpyC 6 H 4 )}{κ 3 - N, C, N -(dpyb)} ( 5 ), respectively. Similar reactions of the Williams’s dimer [IrCl(μ-Cl){κ 3 - N, C, N -(dpyMeb)}] 2 with HNImpyC 6 H 5 and HNBzimpyC 6 H 5 in the presence of Na 2 CO 3 afford the dimethylated counterparts Ir{κ 3 - C, N, N -(NImpyC 6 H 4 )}{κ 3 - N, C, N -(dpyMeb)} ( 6 ) and Ir{κ 3 - C, N, N -(NBzimpyC 6 H 4 )}{κ 3 - N, C, N -(dpyMeb)} ( 7 ), whereas 2-(6-phenylpyridine-2-yl)-1 H -indole (HIndpyC 6 H 5 ) initially gives IrH{κ 2 - N, N -(IndpyC 6 H 5 )}{κ 3 - N, C, N -(dpyMeb)} ( 8 ) and subsequently Ir{κ 3 - C, N, N -(IndpyC 6 H 4 )}{κ 3 - N, C, N -(dpyMeb)} ( 9 ). Complexes 4 – 7 are phosphorescent green emitters (λ em 490–550 nm), whereas 9 is greenish yellow emissive (λ em 547–624 nm). They display lifetimes in the range 0.5–9.7 μs and quantum yields in both doped poly(methyl)methacrylate films and in 2-methyltetrahydrofuran at room temperature depending upon the ligands: 0.5–0.7 for 6 and 7, about 0.4 for 4 and 5, and 0.3–0.2 for 9 .