Homologous Series of Phenylquinoline-Carbazole Main Ligand Based On Red-Emitting Iridium(III) Complexes for Phosphorescent Organic Light-Emitting Diodes

New red-emitting phosphorescent Ir(III) complexes, bis[9-ethyl-2-(4-phenylquinolin-2-yl)-9 H -carbazolato-N,C 2′ ]iridium picolinate- N -oxide [(2-Et-CVz-PhQ) 2 Ir(pic-N-O)] and bis[9-ethyl-3-(4-phenylquinolin-2-yl)-9 H -carbazolato-N,C 2′ ]iridium picolinate- N -oxide (3-Et-CVz-PhQ) 2 Ir(pic-N-O), were synthesized, and their applications in phosphorescent organic light-emitting diodes (PhOLEDs) as well as their photophysical, electrochemical, and electroluminescent (EL) properties were investigated. To tune the performance of PhOLEDs containing these substances, the 9-ethyl-2-(4-phenylquinolin-2-yl)-9 H -carbazole (2-Et-CVz-PhQ) and 9-ethyl-3-(4-phenylquinolin-2-yl)-9 H -carbazole (3-Et-CVz-PhQ) were prepared and used as main ligands for the synthesis of Ir(III) complexes. The solution processed red PhOLEDs with a configuration of ITO/PEDOT:PSS/TCTA/PVK or 3-Et-CVz-PhQ:TPD:OXD-7:Ir complex/cathode were fabricated. The maximum EL emission peaks of (2-Et-CVz-PhQ) 2 Ir(pic-N-O) and (3-Et-CVz-PhQ) 2 Ir(pic-N-O) were observed at 689 and 609 nm, respectively. The PhOLEDs with (2-Et-CVz-PhQ) 2 Ir(pic-N-O) and (3-Et-CVz-PhQ) 2 Ir(pic-N-O) exhibited respective maximum external quantum efficiencies of 4.32% and 8.74% along with CIE (Commission International de l’Eclairage) coordinates of (0.68, 0.28) and (0.62, 0.37), respectively. Furthermore, by introducing a TCTA interlayer, the PhOLEDs showed a slight efficiency roll off of 15% from a low current density (1 mA/cm 2 ) to a high current density (30 mA/cm 2 ). The electro-optical properties and the performance of PhOLEDs, prepared by using the two Ir(III) complexes, were probed through the use of density functional theory (DFT) calculations.