Pseudo-Tris(heteroleptic) Red Phosphorescent Iridium(III) Complexes Bearing a Dianionic C, N, C', N'-Tetradentate Ligand

Abstract

1-Phenyl-3-(1-phenyl-1-(pyridin-2-yl)ethyl)isoquinoline (H₂MeL) has been prepared by Pd(N-XantPhos)-catalyzed "deprotonative cross-coupling processes" to synthesize new phosphorescent red iridium(III) emitters (601-732 nm), including the carbonyl derivative Ir(κ⁴-cis-C,C'-cis-N,N'-MeL)Cl(CO) and the acetylacetonate compound Ir(κ⁴-cis-C,C'-cis-N,N'-MeL)(acac). The tetradentate 6e-donor ligand (6tt') of these complexes is formed by two different bidentate units, namely, an orthometalated 2-phenylisoquinoline and an orthometalated 2-benzylpyridine. The link between the bidentate units reduces the number of possible stereoisomers of the structures [6tt' + 3b] (3b = bidentate 3e-donor ligand), with respect to a [3b + 3b' + 3b″] emitter containing three free bidentate units, and it permits a noticeable stereocontrol. Thus, the isomers fac-Ir(κ⁴-cis-C,C'-cis-N,N'-MeL){κ²-C,N-(C₆H₄-py)}, mer-Ir(κ⁴-cis-C,C'-cis-N,N'-MeL){κ²-C,N-(C₆H₃R-py)}, and mer-Ir(κ⁴-trans-C,C'-cis-N,N'-MeL){κ²-C,N-(C₆HR-py)} (R = H, Me) have also been selectively obtained. The new emitters display short lifetimes (0.7-4.6 μs) and quantum yields in a doped poly(methyl methacrylate) film at 5 wt % and 2-methyltetrahydrofuran at room temperature between 0.08 and 0.58. The acetylacetonate complex Ir(κ⁴-cis-C,C'-cis-N,N'-MeL)(acac) has been used as a dopant for a red PhOLED device with an electroluminescence λ_max of 672 nm and an external quantum efficiency of 3.4% at 10 mA/cm².