title: Design and synthesis of iridium bis(carbene) complexes for efficient blue electrophosphorescence.
abstract: Five iridium bis(carbene) complexes, [Ir(pmi)(2)(pypz)] (1), [Ir(mpmi)(2)(pypz)] (2), [Ir(fpmi)(2)(pypz)] (3), [Ir(fpmi)(2)(pyim)] (4), and [Ir(fpmi)(2)(tfpypz)] (5) (pmi=1-phenyl-3-methylimdazolin-2-ylidene-C,C(2'); fpmi=1-(4-fluorophenyl)-3-methylimdazolin-2-ylidene-C,C(2'); mpmi=1-(4-methyl-phenyl)-3-methylimdazolin-2-ylidene-C,C(2'); pypz=2-(1H-pyrazol-5-yl)pyridinato; pyim=2-(1H-imidazol-2-yl)pyridinato; and tfpypz=2-(3-(trifluoromethyl)-1H-pyrazol-5-yl)pyridinato), were synthesized and their structures were characterized by NMR spectroscopy, mass spectroscopy and X-ray diffraction. These complexes showed phosphorescent emission with the emission maxima between 453 and 490 nm. Various spectrophotometric measurements, cyclic voltammetric studies, and density functional theory (DFT) calculations show that, unlike most of the phosphorescent cyclometalated iridium complexes, the lowest unoccupied molecular orbital (LUMO) energy and the emissive state of these iridium complexes are mainly controlled by the N,N'-heteroaromatic (N^N) ligand. Despite the fact that the LUMO levels of these complexes are mainly on the N^N ligands, the efficiencies of the electroluminescent (EL) devices are very high. For example, the EL devices using [Ir(mpmi)(2)(pypz)], [Ir(fpmi)(2)(pypz)], and [Ir(fpmi)(2)(tfpypz)] as the dopant emitters exhibited light- to deep-blue electrophosphorescence with external quantum efficiencies of 15.2, 14.1, and 7.6% and Commission Internationale d'Énclairage (x,y) coordinates (CIE(x,y)) of (0.14, 0.27), (0.14, 0.18) and (0.14, 0.10), respectively.
authors: Department of Chemistry, National Tsing Hua University, Hsinchu 30013, Taiwan.
authors: Cheng-Han
authors: CH
authors: Hsieh
authors: Fang-Iy
authors: FI
authors: Wu
authors: Chun-Hsiang
authors: CH
authors: Fan
authors: Min-Jie
authors: MJ
authors: Huang
authors: Kun-Yi
authors: KY
authors: Lu
authors: Pei-Yu
authors: PY
authors: Chou
authors: Yu-Han Ou
authors: YH
authors: Yang
authors: Shih-Hsiang
authors: SH
authors: Wu
authors: I-Chia
authors: IC
authors: Chen
authors: Shu-Hua
authors: SH
authors: Chou
authors: Ken-Tsung
authors: KT
authors: Wong
authors: Chien-Hong
authors: CH
authors: Cheng