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Homoleptic Tris(Pyridyl Pyrazolate) Ir III Complexes: En Route to Highly Efficient Phosphorescent OLEDs
Author(s) -
Chen Kellen,
Yang ChengHan,
Chi Yun,
Liu ChaoShiuan,
Chang ChihHao,
Chen ChungChia,
Wu ChungChih,
Chung MinWen,
Cheng YiMing,
Lee GeneHsiang,
Chou PiTai
Publication year - 2010
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200902902
Subject(s) - homoleptic , phosphorescence , chemistry , pyrazole , trifluoromethyl , iridium , oled , crystallography , luminescence , ligand (biochemistry) , single crystal , medicinal chemistry , photochemistry , metal , alkyl , fluorescence , materials science , catalysis , organic chemistry , biochemistry , physics , optoelectronics , receptor , layer (electronics) , quantum mechanics
Treatment of the metal reagent IrCl 3 ⋅ n H 2 O with two equivalents of 2‐pyridyl pyrazole (N^N)H (3‐ tert ‐butyl‐5‐(2‐pyridyl) pyrazole, (bppz)H and 3‐trifluoromethyl‐5‐(2‐pyridyl) pyrazole, (fppz)H), afforded the isomeric Ir III metal complexes with a general formula cis ‐[Ir(bppz) 2 Cl 2 ]H ( 2 a ), trans ‐[Ir(bppz) 2 Cl 2 ]H ( 3 a ), cis ‐[Ir(fppz) 2 Cl 2 ]H ( 2 b ), and trans ‐[Ir(fppz) 2 Cl 2 ]H ( 3 b ). Single‐crystal X‐ray diffraction studies on 2 b and 3 a revealed the coexistence of two pyrazolate chelates and two terminal chloride ligands on the coordination sphere. Subsequent reactivity studies confirmed their intermediacy to the preparation of homoleptic mer ‐[Ir(bppz) 3 ] ( 1 a ) and mer ‐[Ir(fppz) 3 ] ( 1 b ) that showed dual intraligand and ligand‐to‐ligand charge‐transfer phosphorescence at room temperature. To attain bright, room‐temperature phosphorescence further, we then synthesized two isoquinolinyl pyrazolate complexes, mer ‐[Ir(bipz) 3 ] ( 4 a ) and mer ‐[Ir(fipz) 3 ] ( 4 b ) ((bipz)H=3‐ tert ‐butyl‐5‐(1‐isoquinolyl) pyrazole and (fipz)H=3‐trifluoromethyl‐5‐(1‐isoquinolyl) pyrazole). Their orange luminescence is mainly attributed to the mixed MLCT/ππ* transition, and the quantum yields were as high as 86 ( 4 a ) and 50 % ( 4 b ) in degassed CH 2 Cl 2 solution at RT. The organic light‐emitting diodes (OLEDs) were then fabricated by using 4 a as a dopant, giving orange luminescence with CIE x , y =0.55, 0.45 (CIE x , y =the 1931 Commission Internationale de L’Eclairage ( x , y ) coordinates) and peak efficiencies of 14.6 % photon/electron, 34.8 cd A −1 , 26.1 lm W −1 . The device data were then compared with the previously reported heteroleptic complex [Ir(dfpz) 2 (bipz)] ( 5 ) ((dfpz)H=1‐(2,4‐difluorophenyl) pyrazole), revealing the possible effect of the bipz chelate and phosphor design on the overall electrophosphorescent performance, which can be understood by the differences in the carrier‐transport properties.