Journal
CHEMISTRY-A EUROPEAN JOURNAL
Volume 17, Issue 33, Pages 9180-9187Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.201100317
Keywords
carbenes; iridium; phosphorescence; photochromism; organic light-emitting diodes; thin films
Categories
Funding
- Ministry of Economic Affairs [95-EC-17A-08-S1-042, 98-EC-17A-08-S1-042]
- National Science Council (NSC) of the Republic of China [95-2119M-007-005, 97-3114M-007-002]
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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, C2'; 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 boolean AND N) ligand. Despite the fact that the LUMO levels of these complexes are mainly on the N boolean AND 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'Enclairage (x, y) coordinates (CIEx,y) of (0.14, 0.27), (0.14, 0.18) and (0.14, 0.10), respectively.
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