Bipolar Heteroleptic Green Iridium Dendrimers Containing Oligocarbazole and Oxadiazole Dendrons for Bright and Efficient Nondoped Electrophosphorescent Devices

Authors

  • Lingcheng Chen,

    1. State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022 (P. R. China), Fax: (+86) 431-85685653
    2. Graduate School of Chinese Academy of Sciences, Beijing 100039 (P. R. China)
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  • Dr. Junqiao Ding,

    Corresponding author
    1. State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022 (P. R. China), Fax: (+86) 431-85685653
    • State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022 (P. R. China), Fax: (+86) 431-85685653

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  • Prof. Yanxiang Cheng,

    1. State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022 (P. R. China), Fax: (+86) 431-85685653
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  • Prof. Zhiyuan Xie,

    1. State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022 (P. R. China), Fax: (+86) 431-85685653
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  • Prof. Lixiang Wang,

    Corresponding author
    1. State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022 (P. R. China), Fax: (+86) 431-85685653
    • State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022 (P. R. China), Fax: (+86) 431-85685653

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  • Prof. Xiabin Jing,

    1. State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022 (P. R. China), Fax: (+86) 431-85685653
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  • Prof. Fosong Wang

    1. State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022 (P. R. China), Fax: (+86) 431-85685653
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Abstract

Bipolar heteroleptic green light-emitting iridium (Ir) dendrimers and have been designed and synthesized under mild conditions in high yields, in which the first C^N and second O^O ligands are functionalized with oligocarbazole- and oxadiazole-based dendrons, respectively. To avoid affecting the optical properties of the emissive iridium core, all the functional moieties are attached to the ligands through a flexible spacer. Compared with the unipolar dendrimer G(acac), dendrimers and exhibit the close emission maxima of 511–512 nm and photoluminescence quantum yield of 0.39–0.40 in a solution of toluene. Moreover, on going from to and , we have found that the introduction of oxadiazole fragments decreases the lowest unoccupied molecular orbital (LUMO) energy levels to facilitate the electron injection and electron transporting, while their highest occupied molecular orbital (HOMO) energy levels remain unchanged. This means that, we can individually tune the HOMO and LUMO energy levels based on the heteroleptic structure to ensure the relative independence between the hole and electron in the emitting layer (EML), which is a favorable feature for bipolar optoelectronic materials. As a result, a bilayer nondoped electrophosphorescent device with as the EML gives a maximum luminous efficiency of 25.5 cd A−1 (ηext: 7.4 %) and a brightness of 33 880 cd m−2. In comparison to (17.2 cd A−1, 17 680 cd m−2), both the efficiency and brightness are improved by about 1.5 and 2 times, respectively. These state-of-the-art performances indicate the potential of these bipolar heteroleptic iridium dendrimers as solution-processible emitting materials for nondoped device applications.

Abstract

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