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Amorphous Diphenylaminofluorene-Functionalized Iridium Complexes for High-Efficiency Electrophosphorescent Light-Emitting Diodes

Authors

  • W.-Y. Wong,

    1. Department of Chemistry and Centre for Advanced Luminescence Materials, Hong Kong Baptist University, Waterloo Road, Kowloon Tong, Hong Kong, P.R. China
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  • G.-J. Zhou,

    1. Department of Chemistry and Centre for Advanced Luminescence Materials, Hong Kong Baptist University, Waterloo Road, Kowloon Tong, Hong Kong, P.R. China
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  • X.-M. Yu,

    1. Department of Electronic and Electrical Engineering and Centre for Display Research, The Hong Kong University of Science and Technology, Clearwater Bay, Hong Kong, P.R. China
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  • H.-S. Kwok,

    1. Department of Electronic and Electrical Engineering and Centre for Display Research, The Hong Kong University of Science and Technology, Clearwater Bay, Hong Kong, P.R. China
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  • B.-Z. Tang

    1. Department of Chemistry and Centre for Display Research, The Hong Kong University of Science and Technology, Clearwater Bay, Hong Kong, P.R. China
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  • This work was supported by a CERG Grant from the Hong Kong Research Grants Council (HKBU2022/03P) and a Faculty Research Grant from the Hong Kong Baptist University (FRG/04-05/II-59).

Abstract

Two new phosphorescent iridium(III) cyclometalated complexes, [Ir(DPA-Flpy)3] (1) and [Ir(DPA-Flpy)2(acac)] (2) ((DPA-Flpy)H = (9,9-diethyl-7-pyridinylfluoren-2-yl)diphenylamine, Hacac = acetylacetone), have been synthesized and characterized. The incorporation of electron-donating diphenylamino groups to the fluorene skeleton is found to increase the highest occupied molecular orbital (HOMO) levels and add hole-transporting ability to the phosphorescent center. Both complexes are highly amorphous and morphologically stable solids and undergo glass transitions at 160 and 153 °C, respectively. These iridium phosphors emit bright yellow to orange light at room temperature with relatively short lifetimes (< 1 μs) in both solution and the solid state. Organic light-emitting diodes (OLEDs) fabricated using 1 and 2 as phosphorescent dopant emitters constructed with a multilayer configuration show very high efficiencies. The homoleptic iridium complex 1 is shown to be a more efficient electrophosphor than the heteroleptic congener 2. Efficient electrophosphorescence with a maximum external quantum efficiency close to 10 % ph/el (photons per electron), corresponding to a luminance efficiency of ∼ 30 cd A–1 and a power efficiency of ∼ 21 lm W–1, is obtained by using 5 wt.-% 1 as the guest dopant.

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