Synthesis and characterization of blue-emitting Ir(III) complexes with multi-functional ancillary ligands for solution-processed phosphorescent organic light-emitting diodes

A series of Ir(III) complexes, (dfpmpy)(2)Ir(pic), (dfpmpy)(2)Ir(EO2-pic), (dfpmpy)(2)Ir(pic-N-O), and (dfpmpy)(2)Ir(EO2-pic-N-O), containing 2-(2,4-difluorophenyl)-4-methylpyridine (dfpmpy) based main ligand with varying ancillary ligands such as picolinic acid (pic), 4-(2-ethoxyethoxy)picolinic acid (EO2-pic), picolinic acid N-oxide (pic-N-O), and 4-(2-ethoxyethoxy) picolinic acid N-oxide (EO2-pic-N-O), respectively were successfully synthesized for highly efficient blue phosphorescent organic light-emitting diodes (PhOLEDs). The photophysical, electrochemical, and electroluminescent (EL) properties were systematically correlated. The solubilizing 2-ethoxyethanol (EO2-) group was attached to the ancillary ligand through tandem reaction. All of the Ir(III) complexes show high thermal stability and good photoluminescence quantum yields (Phi(pl)) in film state. Solution-processed PhOLEDs were fabricated using these Ir(III) complexes as dopants and achieved a maximum external quantum efficiency (EQE) of 10.9% and current efficiency of 21.15 cd/A for (dfpmpy)(2)Ir(EO2-pic). All the Ir(III) complexes emitted blue light with color purity at the Commission Internationale de L'Eclairage (CIE) coordinates of (0.15, 0.31). (C) 2014 Elsevier B.V. All rights reserved.