Synthesis, characterization of the phenylquinoline-based on iridium(III) complexes for solution processable phosphorescent organic light-emitting diodes

A new series of highly efficient Ir(III) complexes, (DPQ) ₂Ir(pic-N-O), (F₄PPQ)₂Ir(pic-N-O), (FPQ) ₂Ir(pic-N-O), and (CPQ)2Ir(pic-N-O) were synthesized for phosphorescent organic light-emitting diodes (PhOLEDs), and their photophysical, electrochemical, and electroluminescent (EL) properties were investigated. The Ir(III) complexes, including picolinic acid N-oxide (pic-N-O) ancillary ligand, are comprised with the various main ligands such as 2,4-diphenylquinoline (DPQ), 4-phenyl-2-(2,3,4,5-tetrafluorophenyl)quinoline (F4PPQ), 2-(9,9-diethyl-9H- fluoren-2-yl)-4-phenylquinoline (FPQ) and 9-ethyl-3-(4-phenylquinolin-2-yl)-9H- carbazole. Remarkably, high performance PhOLEDs using a solution-processable (DPQ)₂Ir(pic-N-O) doped CBP host emission layer were fabricated to give a high luminance efficiency (LE) of 26.9 cd/A, equivalent to an external quantum efficiency (EQE) of 14.2%. The calculated HOMO-LUMO energy gaps for (DPQ)₂Ir(pic-N-O), (F₄PPQ)₂Ir(pic-N-O), (FPQ)₂Ir(pic-N-O) and (CPQ)2Ir(pic-N-O) were in good agreement with the experimental results.