Synthesis and Characterization of Red-Emitting Iridium(III) Complexes for Solution-Processable Phosphorescent Organic Light-Emitting Diodes

A new series of highly efficient red-emitting phosphorescent Ir(III) complexes, (Et-CVz-PhQ)(2)Ir(pic-N-O), (Et-CVz-PhQ)(2)Ir(pic), (Et-CVz-PhQ)(2)Ir(acac), (EO-CVz-PhQ)(2)Ir(pic-N-O), (EO-CVz-PhQ)(2)Ir(pic), and (EO-CVz-PhQ)(2)Ir(acac), based on carbazole (CVz)-phenylquinoline (PhQ) main ligands and picolinic acid N-oxide (pic-N-O), picolinic acid (pic), and acetylacetone (acac) ancillary ligands, are synthesized for phosphorescent organic light-emitting diodes (PhOLEDs), and their photophysical, electrochemical, and electroluminescent (EL) properties are investigated. All of the Ir(III) complexes have high thermal stability and emit an intense red light with an excellent color purity at CIE coordinates of (0.65,0.34). Remarkably, high-performance solution-processable PhOLEDs were fabricated using Ir(III) complexes with a pic-N-O ancillary ligand with a maximum external quantum efficiency (5.53%) and luminance efficiency (8.89 cd A(-1)). The novel use of pic-N-O ancillary ligand in the synthesis of phosphorescent materials is reported. The performance of PhOLEDs using these Ir(III) complexes correlates well with the results of density functional theory calculations.