Novel heteroleptic iridium(III) complexes with a 2-(1H-pyrazol-5-yl)pyridine derivative containing a carbazole group as ancillary ligand: Synthesis and application for polymer light-emitting diodes

A novel organic compound 9-(2-ethylhexyl)-3-(5-(pyridin-2-yl)-1H-pyrazol-3-yl)-9H-carbazole (PPC) was synthesized and used as ancillary ligand in heteroleptic iridium(III) complexes (npy)2Ir(PPC), (ppy)2Ir(PPC) and (dfppy)2Ir(PPC) (npy: 2-(naphthalen-1-yl)pyridine; ppy: 2-phenylpyridine; dfppy: 2-(2,4-difluorophenyl)pyridine). All of the iridium(III) complexes are amorphous and have high thermal stability. Their glass-transition temperatures are 171 °C, 172 °C and 165 °C, and 5% weight-reduction temperatures are 411 °C, 406 °C and 433 °C, respectively. The polymer light-emitting diodes using the iridium(III) complexes as phosphorescent dopants exhibited good EL performance, the maximum luminances of (npy)2Ir(PPC), (ppy)2Ir(PPC) and (dfppy)2Ir(PPC) are 4948 cd m−2, 11215 cd m−2 and 4696 cd m−2, and the maximum current efficiencies are 11.6 cd A−1, 25.2 cd A−1 and 16.4 cd A−1, respectively. The CIEs of their devices are around (0.59, 0.40), (0.31, 0.57) and (0.32, 0.54), respectively.