A new structural class of mixed-carbene cyclometalated iridium complexes with intense, high-purity blue luminescence are described.

In this work, we describe the emission properties of 12 heteroleptic bis-cyclometalated iridium complexes immobilized in poly­(methyl methacrylate) (PMMA) thin films. The compounds chosen for this study span a range of emission colors covering the visible spectrum and fall into three categories with electronically diverse ancillary ligandsfour cationic bis­(aryl isocyanide) complexes, four with chelating bis­(acyclic diaminocarbene) (bis-ADC) ancillary ligands which can exist in two protonation states, and four neutral compounds with monoanionic, strongly π donating β-ketoiminate (acNac) and β-diketiminate (NacNac) ancillary ligands. Included in this suite of compounds are five new compounds, one with two aryl isocyanide ancillary ligands, two with bis-ADC ancillary ligands, and one each with acNac and NacNac; their syntheses are described, and crystal structures of three are presented. The bulk of the work presented here describes the emission spectra of all 12 compounds, comparing spectral features in solution to those in thin PMMA films (2 wt % of the respective iridium complex). The emission wavelengths and spectral profiles do not change substantially in PMMA films, but in most cases there are dramatic (2-fold to more than 10-fold) increases in photoluminescence quantum yields, with many of the compounds approaching unity quantum yield in PMMA. The increases in quantum yield come from a combination of larger radiative rates and smaller nonradiative rates in the thin film samples, with significant differences between the members of this series of compounds.

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Ligand-centered functionalization reactions offer diverse strategies to prepare luminescent organometallic compounds. These compounds can have unique structures that are not accessible via traditional coordination chemistry and can possess enhanced or unusual photophysical properties. Here we show that bis-cyclometalated iridium bis-isocyanide complexes (1) react with azide (N3 –) to form novel luminescent structures. The fate of the reaction with azide is determined primarily by the substituent on the aryl isocyanide. Those with electron-withdrawing substituents (CF3 or NO2) react with 1 equiv of azide followed by N2 extrusion, forming aryl cyanamido products (2). With electron-donating groups on the aryl isocyanide the reactivity is more diverse, and three outcomes are possible. In two cases, the isocyanide and azide undergo a [3 + 2] cycloaddition to form a C-bound tetrazolato structure (3). In three other cases, 2 equiv of azide are involved in the formation of a previously unobserved structure, where a tetrazolato and aryl cyanamido couple and rearrange to form a chelating ligand comprised of an N-bound tetrazolato and an acyclic diaminocarbene (4). Finally, a bimetallic aryl cyanamido complex (5) is isolated in one case. All compounds are luminescent, some with exceptional photoluminescence quantum yields as high as 0.81 in solution for sky-blue emission, and 0.87 for yellow emission and 0.65 for orange-red emission in polymer films.

In this paper, we report a series of six neutral, bluephosphorescent cyclometalated iridium complexes of the type Ir(C^Y) 2 (CNAr)(CN). The cyclometalating ligands in these compounds (C^Y) are either aryl-substituted 1,2,4-triazole or NHC ligands, known to produce complexes with blue phosphorescence. These cyclometalating ligands are paired with π-acidic, strongly σdonating cyano and aryl isocyanide (CNAr) ancillary ligands, the hypothesis being that these ancillary ligands would destabilize the higher-lying ligand-field (d−d) excited states, allowing efficient blue photoluminescence. The compounds are prepared by substituting the cyanide ancillary ligand onto a chloride precursor and are characterized by NMR, mass spectrometry, infrared spectroscopy, and, for five of the compounds, by X-ray crystallography. Cyclic voltammetry establishes that these compounds have large HOMO− LUMO gaps. The mixed cyano-isocyanide compounds are weakly luminescent in solution, but they phosphoresce with moderate to good efficiency when doped into poly(methyl methacrylate) films, with Commission Internationale de L'Eclairage coordinates that indicate deep blue emission for five of the six compounds. The photophysical studies show that the photoluminescence quantum yields are greatly enhanced in the cyano complexes relative to the chloride precursors, affirming the benefit of strong-field ancillary ligands in the design of blue-phosphorescent complexes. Density functional theory calculations confirm that this enhancement arises from a significant destabilization of the higher-energy ligand-field states in the cyanide complexes relative to the chloride precursors.