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Red‐Emitting Polyfluorenes Grafted with Quinoline‐Based Iridium Complex: “Simple Polymeric Chain, Unexpected High Efficiency”
Author(s) -
Ma Zhihua,
Ding Junqiao,
Zhang Baohua,
Mei Chongyu,
Cheng Yanxiang,
Xie Zhiyuan,
Wang Lixiang,
Jing Xiabin,
Wang Fosong
Publication year - 2010
Publication title -
advanced functional materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 6.069
H-Index - 322
eISSN - 1616-3028
pISSN - 1616-301X
DOI - 10.1002/adfm.200901595
Subject(s) - iridium , phosphorescence , materials science , quinoline , electroluminescence , oled , luminous efficacy , quantum efficiency , photochemistry , polyfluorene , benzothiazole , optoelectronics , fluorescence , nanotechnology , layer (electronics) , chemistry , organic chemistry , physics , optics , catalysis
A series of red‐light emitting electrophosphorescent polyfluorenes (PFs) with varying content of a quinoline‐based iridium complex, (PPQ) 2 Ir(acac) (bis(2,4‐diphenylquinolyl‐N,C 2′ ) iridium(acetylacetonate)), in the side chain are synthesized by Suzuki polycondensation. Because of the efficient Förster energy transfer from the PF main chain to (PPQ) 2 Ir(acac) and direct charge trapping on the complex, the electroluminescent emission from PF is nearly completely quenched, even though the amount of iridium complex incorporated into the polymers is as low as 1 mol %. Based on a single‐layer device configuration, a luminous efficiency of up to 5.0 cd A −1 with a luminance of 2000 cd m −2 and Commission Internationale de L'Eclairage coordinates of (0.63, 0.35) ( x , y ) is realized, which is far superior to that of previously reported red‐light emitting PFs containing benzothiazole‐ and isoquinoline‐based iridium complexes. This result is beyond expectations, especially when considering that the simple polymeric chain involved has no additional charge‐transporting moieties. Noticeably, the device efficiency remains as high as 4.2 cd A −1 with a luminance of 4000 cd m −2 even at current densities of 100 mA cm −2 . Further optimization of the device configuration by incorporating an additional electron‐injection layer leads to improved efficiencies of 8.3 and 7.5 cd A −1 at luminances of 100 and 1000 cd m −2 , respectively. This state‐of‐the‐art performance indicates that covalently attaching quinoline‐based iridium complexes to a PF backbone is a simple and effective strategy to develop high‐efficiency red‐light emitting electrophosphorescent polymers.