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Deep-Blue-Emitting Heteroleptic Iridium(III) Complexes Suited for Highly Efficient Phosphorescent OLEDs

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Physikalisches Institut and Center for Nanotechnology (CeNTech), Westfälische Wilhelms-Universität Münster, Heisenbergstrasse 11, 48149 Münster, Germany
BASF SE, 67056 Ludwigshafen, Germany
§ Organisch-Chemisches Institut, Westfälische Wilhelms-Universität Münster, Corrensstrasse 40, 48149 Münster, Germany
Cite this: Chem. Mater. 2012, 24, 19, 3684–3695
Publication Date (Web):August 25, 2012
https://doi.org/10.1021/cm3010453
Copyright © 2012 American Chemical Society

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    Abstract

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    We report on the design, synthesis, and characterization of four new heteroleptic iridium(III) complexes bearing 2′,6′-difluoro-2,3′-bipyridine and pyridyl-azole ligands. The photophysical properties and cyclic voltammetry of the complexes were also investigated. All compounds display highly efficient genuine blue phosphorescence (λmax ca. 440 nm), at room temperature in solution and in thin film, with quantum yield in the range 0.77–0.87 and 0.62–0.93, respectively. We found that introduction of the bulky tert-butyl substituents on the cyclometalated or azolated chelates can effectively reduce detrimental aggregation, which results in a loss of color purity. Comprehensive density functional theory (DFT) and time-dependent DFT (TD-DFT) approaches have been performed on the ground and excited states of the here reported complexes, in order to gain deeper insights into their structural and electronic features as well as to ascertain the nature of the excited states involved into the electronic absorption processes. Moreover, electron spin density analysis and total electron density difference at the lowest-lying triplet state (T1) were performed for shedding light onto the nature of the emitting excited state. Finally, the fabrication of the organic light-emitting diodes (OLEDs), employing the bulkiest derivative among the here reported phosphorescent dopants, was successfully made. The devices exhibit remarkable maximum external quantum efficiency (EQE) as high as 7.0%, in nonoptimized devices, and power efficiency (PE) of 4.14 lm W–1, together with a true-blue chromaticity CIEx,y = 0.159, 0.185 recorded at 300 cd m–2.

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    X-ray crystallographic data file (CIF) for complexes 1 and 4. ORTEP diagram of 4 and crystal data and structure refinement parameters for complexes 1 and 4. Emission spectra of complex 3 and 4 in thin film. Isodensity surface plots, comparison between experimental and theoretical absorption spectra, geometrical parameters, energy of selected molecular orbital and list of the optical computed vertical transitions for all the complexes. Cyclic voltammograms of complexes 14 recorded in acetonitrile. EL spectra of the devices using complex 1 and 4. This material is available free of charge via the Internet at http://pubs.acs.org.

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