Ir(III)-Based Phosphors with Bipyrazolate Ancillaries; Rational Design, Photophysics, and Applications in Organic Light-Emitting Diodes

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• 作者：Jia-Ling Liao ; Yun Chi ; Zong-Ting Sie ; Chia-Hao Ku ; Chih-Hao Chang ; Mark A. Fox ; Paul J. Low ; Meu-Rurng Tseng ; Gene-Hsiang Lee
• 刊名：Inorganic Chemistry
• 出版年：2015
• 出版时间：November 16, 2015
• 年：2015
• 卷：54
• 期：22
• 页码：10811-10821
• 全文大小：670K
• ISSN：1520-510X

文摘

A series of three charge-neutral Ir(III) complexes bearing both neutral chelating ligands 4,4鈥?di-t-butyl-2,2鈥?bipyridine (dtbbpy) and monoanionic cyclometalated ligands derived from 2-phenylpyridine (ppyH), together with either two monoanionic ligands (i.e., chloride and monodentate pyrazolate) or a single dianionic chelate derived from 5,5鈥?di(trifluoromethyl)-3,3鈥?bipyrazole (bipzH₂) or 5,5鈥?(1-methylethylidene)-bis-(3-trifluoromethyl-1H-pyrazole) (mepzH₂), was successfully synthesized. These complexes are derived from a common, structurally characterized, Ir(III) intermediate complex [Ir(dtbbpy) (ppy)Cl₂] (1), from treatment of IrCl₃路3H₂O with equal amount of the diimine (N^N) and precursor of the cyclometalated (C^N) ligands in a form of one-pot reaction. Treatment of 1 with various functional pyrazoles afforded [Ir(dtbbpy) (ppy) (pz)Cl] (2), [Ir(dtbbpy) (ppy) (bipz)] (3), and [Ir(dtbbpy) (ppy) (mepz)] (4), which display intense room-temperature emission with 位_max spanning the region between 532 and 593 nm in both fluid and solid states. The Ir(III) complexes, 3 and 4, showcase rare examples of three distinctive chelates (i.e., neutral, anionic, and dianionic) assembled around the central Ir(III) cation. Hybrid density functional theory (DFT; B3LYP) electronic structure calculations on 1鈥?b>4 reveal the lowest unoccupied molecular orbital to be 蟺*(bpy) in character for all complexes and highest occupied molecular orbital (HOMO) offering d(Ir)鈭捪€(phenyl) character for 1, 2, and 4 and 蟺(bipz) character for 3. The different HOMO composition of 3 and 4 is also predicted by calculations using pure DFT (BLYP) and wave function (MP2) methods. On the basis of time-dependent DFT calculations, the emissive processes are dominated by the phenyl group-to-bipyridine, ligand_(ppy)-to-ligand_(bpy) charge transfer admixed with metal-to-ligand transition for all Ir(III) complexes. Organic light emitting diodes were successfully fabricated. A double emitting layer design was adopted in the device architecture using Ir(III) metal complexes 3 and 4, attaining peak external quantum efficiencies, luminance efficiencies, and power efficiencies of 18.1% (59.0 cd/A and 38.6 lm/W) and 16.6% (53.3 cd/A and 33.5 lm/W), respectively.