posted on 2016-11-15, 19:18authored byHui-Ting Mao, Chun-Xiu Zang, Li−Li Wen, Guo-Gang Shan, Hai-Zhu Sun, Wen-Fa Xie, Zhong-Min Su
Five neutral heteroleptic
Ir(III) complexes 1–5 using the same
cyclometalated ligand and different pyridine-1,2,4-triazolyl
derivatives as ancillary ligands with fluorine substituents attached,
were rationally designed and prepared. Their photophysical, electrochemical,
and thermal properties were studied, and theoretical calculations
were performed to understand the emission behaviors as well. Introducing
fluorine atoms has little effect on the photophysical and thermal
properties, but the performances of the resulting devices can be fine-tuned.
Among them, a heavy doping level device employing a phosphor with
five fluorine atoms delivers superior device efficiencies with ηc = 32.6 cd A–1 and ηp =
27.6 lm W–1, respectively, which is higher than
those of other counterparts. Importantly, such a device exhibits almost
negligible roll-off in luminance efficiency. Despite nondoped devices
achieving good EL performance, more fluorine atoms lead to a relatively
higher efficiency roll-off. The results suggest that rational incorporation
of fluorine atoms into the ancillary ligands can significantly improve
the performance of devices with features of high efficiency and small
roll-off.