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

• Published in: Chemistry : a European journal Vol. 25; no. 67; pp. 15375 - 15386
• Main Authors: Hsu, Ling-Yang, Liang, Qiumin, Wang, Zhiheng, Kuo, Hsin-Hung, Tai, Wun-Shan, Su, Shi-Jian, Zhou, Xiuwen, Yuan, Yi, Chi, Yun
• Format: Journal Article
• Language: English
• Published: Germany 02.12.2019
• Subjects: iridium; chelates; ligand design; luminescence; organic light-emitting diodes
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201903707

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 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 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) ] 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 ) of 18.7 % and CIE coordinates of (0.145, 0.218), with a slightly reduced EQE of 13.7 % at 100 cd m due to efficiency roll-off.