Efficient Blue Electrophosphorescence and Hyperphosphorescence Generated by Bis-tridentate Iridium(III) Complexes

Ze-Lin Zhu; Premkumar Gnanasekaran; Jie Yan; Zhong Zheng; Chun-Sing Lee; Yun Chi; Xiuwen Zhou

doi:10.1021/acs.inorgchem.2c01026

Efficient Blue Electrophosphorescence and Hyperphosphorescence Generated by Bis-tridentate Iridium(III) Complexes

Inorg Chem. 2022 Jun 13;61(23):8898-8908. doi: 10.1021/acs.inorgchem.2c01026. Epub 2022 May 30.

Authors

Ze-Lin Zhu¹, Premkumar Gnanasekaran², Jie Yan¹, Zhong Zheng¹, Chun-Sing Lee¹, Yun Chi^{1

2}, Xiuwen Zhou³

Affiliations

¹ Department of Materials Science and Engineering, Department of Chemistry, and Center of Super-Diamond Advanced Films, City University of Hong Kong, Kowloon Tong 999077, Hong Kong SAR, China.
² Frontier Research Center on Fundamental and Applied Sciences of Matters and Department of Chemistry, National Tsing Hua University, Hsinchu 30013, Taiwan.
³ School of Mathematics and Physics, The University of Queensland, Brisbane, Queensland 4072, Australia.

PMID: 35635511
DOI: 10.1021/acs.inorgchem.2c01026

Abstract

Four blue-emissive iridium(III) complexes bearing a 3,3'-(1,3-phenylene)bis[1-isopropyl-6-(trifluoromethyl)-3H-imidazo[4,5-b]pyridin-2-ylidene]-based pincer chelate, which are derived from PXn·H₃(PF₆)₂, where n = 1-4, and a cyclometalating chelate given from 9-[6-[5-(trifluoromethyl)-2λ²-pyrazol-3-yl]pyridin-2-yl]-9H-carbazole [(PzpyCz)H₂], were successfully synthesized and employed as both an emissive dopant and a sensitizer in the fabrication of organic light-emitting diode (OLED) devices. These functional chelates around a Ir^III atom occupied two mutually orthogonal coordination arrangements and adopted the so-called bis-tridentate architectures. Theoretical studies confirmed the dominance of the electronic transition by the pincer chelates, while the dianionic PzpyCz chelate was only acting as a spectator group. Phosphorescent OLED devices with [Ir(PX3)(PzpyCz)] (B3) as the dopant gave a maximum external quantum efficiency (EQE) of 21.93% and CIE_xy of (0.144, 0.157) and was subjected to only ∼10% of roll-off in efficiency at a high current density of 1000 cd m^-2. Blue-emissive narrow-band hyperphosphorescence was also obtained using B3 as an assistant sensitizer and ν-DABNA as a terminal emitter, giving both an improved EQE of 26.17% and CIE_xy of (0.116, 0.144), confirming efficient Förster resonance energy transfer in this hyperdevice.