Effects of the Methyl Group on the Emission Efficiency of the Red Phosphorescent Iridium(III) Complexes for OLEDs

Novel red phosphorescent iridium(III) complexes, namely (MN-Q)2Ir(tmd), (MN-MQ)2Ir(tmd), (PT-P)2Ir(tmd) and (PT-MP)2Ir(tmd) were synthesized for the red phosphorescent organic lightemitting diodes (phOLEDs). The ligands have sites of both the electron donor and acceptor in a molecule. The main ligands were synthesized by the Suzuki coupling reaction, and comprised an electron donor and an electron acceptor group. Subsequently, the iridium(III) complexes were synthesized by the Nonoyama reaction and their photochemical luminescence properties were investigated by ultraviolet-visible and photoluminescence spectroscopy. The manufactured devices were characterized by current density-voltage-luminance, power efficiency, external quantum efficiency, as well as their electroluminescence spectra. Finally, the effects of the trifluoromethyl group on the emission efficiency of the organic light-emitting diodes were investigated by comparing the energy levels and luminescence efficiency of the three iridium complexes.