Zhang Fuli, Ma Dongxin, Duan Lian, Qiao Juan, Dong Guifang, Wang Liduo, Qiu Yong
College of Chemistry and Chemical Engineering, Shangqiu Normal University , Shangqiu 476000, P. R. China.
Inorg Chem. 2014 Jul 7;53(13):6596-606. doi: 10.1021/ic5001733. Epub 2014 Jun 10.
The development of pure-blue-to-deep-blue-emitting ionic phosphors is an ultimate challenge for full-color displays and white-light sources. Herein we report two series of short-wavelength light-emitting cationic iridium(III) complexes with nonconjugated ancillary and cyclometalating ligands, respectively. In the first series, nonconjugated 1-[(diphenylphosphino)methyl]-3-methylimidazolin-2-ylidene-C,C2' (dppmmi) is used as the ancillary ligand and 2-phenylpyridine (ppy), 2-(2,4-difluorophenyl)pyridine (dfppy), and 1-(2,4-difluorophenyl)-1H-pyrazole (dfppz) are used as cyclometalating ligands. In the second one, nonconjugated 2,4-difluorobenzyl-N-pyrazole (dfbpz) is used as the cyclometalating ligand and 3-methyl-1-(2-pyridyl)benzimidazolin-2-ylidene-C,C(2)' (pymbi) as the ancillary ligand. The synthesis and photophysical and electrochemical properties, together with the X-ray crystal structures of these complexes, have been investigated. At room temperature, blue-emitting complexes [Ir(ppy)2(dppmmi)]PF6 (1) and [Ir(dfppy)2(dppmmi)]PF6 (2; PF6(-) is hexafluorophosphate) show much larger photoluminescence quantum yields of 24% and 46%, respectively. On the contrary, for complexes [Ir(dfppz)2(dppmmi)]PF6 (3) and [Ir(dfbpz)2(pymbi)]PF6 (4), deep-blue luminescence is only observed at low temperature (77 K). Density functional theory calculations are used to rationalize the differences in the photophysical behavior observed upon changes of the ligands. It is shown that the electronic transition dipoles of cationic iridium complexes 1 and 2 are mainly confined to cyclometalated ligands ((3)MLCT and LC (3)π-π*) and those of complex 3 are confined to all of the ligands ((3)MLCT, LC (3)π-π*, and (3)LLCT) because of the high LUMO energy level of dfppz. The emission of 4 mainly originates from the central iridium(III) ion and cyclometalated ligand to ancillary ligand charge transfer ((3)MLCT and (3)LLCT), in contrast to commonly designed cationic complexes using carbene-type ancillary ligands, where emission originates from the cyclometalated main ligands. Solution-processed organic light-emitting diodes based on complexes 1 and 2 gave blue-green (498 nm) and blue (478 nm) electroluminescence with maximum current efficiencies of 3.8 and 3.4 cd A(-1), respectively. The results indicate that introducing nonconjugated ligands into cationic iridium complexes is an effective means of achieving short-wavelength light-emitting phosphors.
开发纯蓝色至深蓝色发光的离子型磷光体是全彩色显示器和白色光源面临的一项终极挑战。在此，我们报道了分别具有非共轭辅助配体和环金属化配体的两个系列的短波长发光阳离子铱（III）配合物。在第一个系列中，非共轭的1-[(二苯基膦基)甲基]-3-甲基咪唑啉-2-亚基-C,C2'（dppmmi）用作辅助配体，2-苯基吡啶（ppy）、2-(2,4-二氟苯基)吡啶（dfppy）和1-(2,4-二氟苯基)-1H-吡唑（dfppz）用作环金属化配体。在第二个系列中，非共轭的2,4-二氟苄基-N-吡唑（dfbpz）用作环金属化配体，3-甲基-1-(2-吡啶基)苯并咪唑啉-2-亚基-C,C(2)'（pymbi）用作辅助配体。对这些配合物的合成、光物理和电化学性质以及X射线晶体结构进行了研究。在室温下，蓝色发光配合物[Ir(ppy)2(dppmmi)]PF6（1）和[Ir(dfppy)2(dppmmi)]PF6（2；PF6(-)为六氟磷酸盐）的光致发光量子产率分别高达24%和46%。相反，对于配合物[Ir(dfppz)2(dppmmi)]PF6（3）和[Ir(dfbpz)2(pymbi)]PF6（4），仅在低温（77 K）下观察到深蓝色发光。采用密度泛函理论计算来合理解释配体变化时观察到的光物理行为差异。结果表明，阳离子铱配合物1和2的电子跃迁偶极主要局限于环金属化配体（(3)MLCT和LC(3)π-π*），而配合物3的则局限于所有配体（(3)MLCT、LC(3)π-π*和(3)LLCT），这是由于dfppz的LUMO能级较高。与通常使用卡宾型辅助配体设计的阳离子配合物不同，4的发射主要源于中心铱（III）离子以及环金属化配体到辅助配体的电荷转移（(3)MLCT和(3)LLCT），在后者中发射源于环金属化主配体。基于配合物1和2的溶液处理有机发光二极管分别发出蓝绿色（498 nm）和蓝色（478 nm）电致发光，最大电流效率分别为3.8和3.4 cd A(-1)。结果表明，将非共轭配体引入阳离子铱配合物是实现短波长发光磷光体的有效手段。
