Near-infrared emission of dinuclear iridium complexes with hole/electron transporting bridging and their monomer in solution processed organic light-emitting diodes

To obtain efficient near-infrared (NIR) emitting materials, a novel iridium (III) complex based on a tri-phenylamine functionalized pyridylpyrene ligand, namely, Mono-Ir, as well as its two corresonding dinuclear iridium (III) complexes possessing pi-conjugated bridging linkages of hole-transporting carbazole (Caz) unit or electron-transporting 2,5-diphenyl-1,3,4-oxadiazole (OXD) unit, namely D-Ir-Caz and D-Ir-OXD, were successfully synthesized and characterized. Under photo-excitation, similar phosphorescence spectrum were obtained for the three complexes with intense NIR emission peak at approximately 698 nm and emission wavelength ranging from 650 to 900 nm. Also, in their single-emissive-layer OLEDs with a device structure of ITO/PEDOT:PSS/TFB/CBP:PBD:complexesam/TmPyPB/Liq/Al, similar NIR electroluminescent (EL) emission peaked at 698 nm with a shoulder at 762 nm were obtained. The Mono-Ir-based device showed an external quantum efficiency (EQE) of 1.29% at low current density of 3.5 mA cm(-2), while a relatively lower efficiency of 0.27% for the D-Ir-Caz-based device and 0.41% for the D-Ir-OXD-based device, accompanied with negligible efficiencies roll-off at high current densities were achieved, respectively. The better device performance should be achieved when coupled with electron transporting bridging, especially at high currents. (C) 2017 Elsevier Ltd. All rights reserved.