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 (H ₂MeL) 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(κ ⁴- cis- C, C′- cis- N, N′-MeL)Cl(CO) and the acetylacetonate compound Ir(κ ⁴- 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(κ ⁴- cis- C, C′- cis- N, N′-MeL){κ ²- C, N-(C ₆H ₄-py)}, mer-Ir(κ ⁴- cis- C, C′- cis- N, N′-MeL){κ ²- C, N-(C ₆H ₃R-py)}, and mer-Ir(κ ⁴- trans- C, C′- cis- N, N′-MeL){κ ²- C, N-(C ₆HR-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(κ ⁴- 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/cm ².

Abstract

The proligand 1-phenyl-3-(1-phenyl-1-(pyridine-2-yl)ethyl)isoquinoline is used to generate a new family of neutral phosphorescent red iridium(III) emitters containing a tetradentate ligand, formed by two different bidentate units, and a third bidentate ligand with a good stereocontrol of the resulting [6tt′ + 3b] products. One of the new emitters has been used in the fabrication of an OLED device.