Two novel orange cationic iridium(III) complexes with multifunctional ancillary ligands used for polymer light-emitting diodes

Two novel orange cationic iridium complexes (npy)₂Ir(o-phen)]PF₆ and (npy)₂Ir(c-phen)]PF₆ were synthesized. Hnpy: 2-(naphthalen-1-yl)pyridine; o-phen: a 1,10-phenanthroline derivative containing an electron-transporting functional group of 2,5-diphenyl-1,3,4-oxadiazole and a crystallization-resistant tert-butyl functional group; c-phen: a 1,10-phenanthroline derivative containing a hole-transporting functional group of carbazole and a crystallization-resistant 2-ethylhexyl functional group. Both of them are amorphous and possess high thermal stability with 5% weight-reduction temperatures (ΔT_5%) of 386 °C and 383 °C, and glass-transition temperatures (T_g) of 267 °C and 195 °C respectively. They were used as phosphorescent dopants in polymer light-emitting diodes (PLEDs) fabricated by solution-processed technology with configuration of ITO/PEDOT:PSS/PVK:PBD:iridium complex/TPBI/CsF/Al. At the optimal doping concentration of 2.0 wt%, the corresponding PLEDs exhibited the maximum current efficiencies of 9.1 cd A⁻¹ and 10.0 cd A⁻¹, the maximum external quantum efficiencies of 6.5% and 7.1%, and the maximum luminance of 2314 cd m⁻² and 3157 cd m⁻² respectively, with the same CIE coordinates of (0.57, 0.40). The results indicate that cationic iridium complexes are promising candidates for PLED applications when they are designed reasonably.