Cationic Ir(III) Complexes with 4-Fluoro-4′-pyrazolyl-(1,1′-biphenyl)-2-carbonitrile as the Cyclometalating Ligand: Synthesis, Characterizations, and Application to Ultrahigh-Efficiency Light-Emitting Electrochemical Cells

Light-emitting electrochemical cells (LECs) promise low-cost, large-area luminescence applications with air-stabilized electrodes and a versatile fabrication that enables the use of solution processes. Nevertheless, the commercialization of LECs is still encountering many obstacles, such as low electroluminescence (EL) efficiencies of the ionic materials. In this paper, we propose five blue to yellow ionic Ir complexes possessing 4-fluoro-4′-pyrazolyl-(1,1′-biphenyl)-2-carbonitrile (ppfn) as a novel cyclometalating ligand and use them in LECs. In particular, the device within di[4-fluoro-4′-pyrazolyl-(1,1′-biphenyl)-2-carbonitrile]-4,4′-di-tert-butyl-2,2′-bipyridyl iridium(III) hexafluorophosphate (DTBP) shows a remarkable photoluminescence quantum yield (PLQY) of 70%, and by adjusting the emissive-layer thickness, the maximal external quantum efficiency (EQE) reaches 22.15% at 532 nm under the thickness of 0.51 μm, showing the state-of-the-art value for the reported blue-green LECs.

Cyclometalated dinuclear iridium complexes with the general formula (C^N)2Ir(μ-Cl)2Ir(C^N)2 were prepared according to literature procedures. 1 Suitable crystal was sealed in thin-walled glass capillaries under a nitrogen atmosphere and mounted on a Bruker AXS SMART 1000 diffractometer.The absorption correction was based on the symmetry equivalent reflections using the SADABS program.The space group determination was based on a check of the Laue symmetry and systematic absences and was confirmed using the structure solution.The structure was solved by direct methods using a SHELXTL package.All non-H atoms were located from successive Fourier maps, and hydrogen atoms were refined using a riding model.Anisotropic thermal parameters were used for all non-H atoms, and fixed isotropic parameters were used for H atoms.
After being cooled to room temperature, the mixture was extracted with ethyl acetate.

Synthesis of [Ir2(ppfn)4Cl2
]. ppfn (0.88 g, 3.4 mmol) was dissolved in 2-ethoxyethanol (40 mL) in a round-bottom flask.Subsequently, Ir(III) chloride hydrate (0.50 g, 1.7 mmol) and 10 mL of water were added to the flask.The reaction mixture was refluxed for 24 h and then cooled to room temperature.The resulting precipitate was collected, washed with water, and dried under vacuum to obtain chloro-bridged Ir dimer [Ir2(ppfn)4Cl2] (1.1 g, 89%) as a gray solid, which was used directly without the need for further purification.

a)
Calculated excitation energies for the triplet states in MeCN solution; b) H and L denote the HOMO and LUMO, respectively; data in parentheses are the contributions of the excitation.

Figure S18 .
Figure S18.T1 excited state geometry of complex DTBP-DFBP obtained in MeCN of

Figure S25 .
Figure S25.EL spectra of the LECs based on complex DTBP with emissive layer

Table S1 .
Crystal data of complex DTBP.