Novel blue-phosphorescent platinum(II) ternary complexes with β-diketonate and fluorinated phenylimidazole for organic light-emitting diodes

In this study, the one-pot synthesis of two novel Pt(II) β-diketonate compounds, namely Pt(tpim)(O^∧ O) (1) and Pt(mtpim)(O^∧ O) (2) (tpim = 1-([1,1^′:3^′,1^{′ ′}-terphenyl]-2^′-yl)-2-(4-fluorophenyl)-1H-imidazole, mtpim = 2-(4-fluorophenyl)-1-(5^′-methyl-[1,1^′:3^′,1^{′ ′}-terphenyl]-2^′-yl)-1H-imidazole, and O^∧ O = acetylacetonato), was achieved. Both compounds had a distorted square-planar ge-ometry without direct intermolecular Pt(II) —Pt(II) interactions, which was attributed to the bulky terphenyl group of the C^∧ N chelate as well as strong intermolecular Pt(II)——H(terphenyl/imidazole) interaction. Compounds 1 and 2 exhibited bright sky-blue-phosphorescent emission with a λ_max = 490 nm and photoluminescence quantum yields of 0.50 and 0.47, respectively. The time-dependent density functional theory calculations revealed that the electronic transitions of both compounds were attributed to the combination of intraligand charge transfer (π_{(phenylimidazole)} –π∗_(terphenyl)) and ligand-to-ligand charge transfer (π_(acac) –π∗_(terphenyl)), in addition to a contribution from the metal-to-ligand charge transfer (Pt_d –π∗_(terphenyl)). Compounds 1 and 2, as the dopants, and 3^′-di(9H-carbazol-9-yl)-1,1^′-biphenyl:9-(3’-carbazol-9-yl-5-cyano-biphenyl-3-yl)-9H-carbazole-3-carbonitrile, as the mixed host were used to fabricate multilayer phosphorescent organic light-emitting diodes. Compound 1 doped in the emissive layer at a 10% doping level demonstrated a maximum current efficiency of 21.7 cd A⁻¹ at 100 cd m⁻².