Bis-tridentate IrIII Phosphors Bearing Two Fused Five-Six-Membered Metallacycles: A Strategy to Improved Photostability of Blue Emitters

Ling-Yang Hsu; Qiumin Liang; Zhiheng Wang; Hsin-Hung Kuo; Wun-Shan Tai; Shi-Jian Su; Xiuwen Zhou; Yi Yuan; Yun Chi

doi:10.1002/chem.201903707

Bis-tridentate Ir^III Phosphors Bearing Two Fused Five-Six-Membered Metallacycles: A Strategy to Improved Photostability of Blue Emitters

Chemistry. 2019 Dec 2;25(67):15375-15386. doi: 10.1002/chem.201903707. Epub 2019 Nov 6.

Authors

Ling-Yang Hsu¹, Qiumin Liang², Zhiheng Wang², Hsin-Hung Kuo¹, Wun-Shan Tai¹, Shi-Jian Su², Xiuwen Zhou³, Yi Yuan⁴, Yun Chi^{1

4}

Affiliations

¹ Department of Chemistry and Frontier Research Center on, Fundamental and Applied Sciences of Matter, National Tsing Hua University, Hsinchu, 30013, Taiwan.
² State Key Laboratory of Luminescent Materials and Devices, and Institute of Polymer Optoelectronic Materials and Devices, South China University of Technology, Guangzhou, 510640, P.R. China.
³ School of Mathematics and Physics, The University of Queensland, Brisbane, Queensland, 4072, Australia.
⁴ Department of Materials Science and Engineering, and Department of Chemistry, City University of Hong Kong, Hong Kong, SAR.

PMID: 31573110
DOI: 10.1002/chem.201903707

Abstract

Iridium complexes bearing chelating cyclometalates are popular choices as dopant emitters in the fabrication of organic light-emitting diodes (OLEDs). In this contribution, we report a series of blue-emitting, bis-tridentate Ir^III complexes bearing chelates with two fused five-six-membered metallacycles, which are in sharp contrast to the traditional designs of tridentate chelates that form the alternative, fused five-five metallacycles. Five Ir^III complexes, Px-21-23, Cz-4, and Cz-5, have been synthesized that contain a coordinated dicarbene pincer chelate incorporating a methylene spacer and a dianionic chromophoric chelate possessing either a phenoxy or carbazolyl appendage to tune the coordination arrangement. All these tridentate chelates afford peripheral ligand-metal-ligand bite angles of 166-170°, which are larger than the typical bite angle of 153-155° observed for their five-five-coordinated tridentate counterparts, thereby leading to reduced geometrical distortion in the octahedral frameworks. Photophysical measurements and TD-DFT studies verified the inherent transition characteristics that give rise to high emission efficiency, and photodegradation experiments confirmed the improved stability in comparison with the benchmark fac-[Ir(ppy)₃ ] in degassed toluene at room temperature. Phosphorescent OLED devices were also fabricated, among which the carbazolyl-functionalized emitter Cz-5 exhibited the best performance among all the studied bis-tridentate phosphors, showing a maximum external quantum efficiency (EQE_max ) of 18.7 % and CIE_x,y coordinates of (0.145, 0.218), with a slightly reduced EQE of 13.7 % at 100 cd m^-2 due to efficiency roll-off.

Keywords: chelates; iridium; ligand design; luminescence; organic light-emitting diodes.

Abstract

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