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

Two dinuclear iridium (III) complexes D-Ir-Caz and D-Ir-OXD grafting hole or electron transporting π-conjugated bridges, and their corresponding monomer Mono-Ir were successfully synthesized and characterized. Under photo-excitation, all these complexes exhibit similar NIR emission peaked at approximately 698 nm in CH2Cl2. Due to a lower degree of spin-orbit coupling (SOC) in a system with centrosymmetric environment at the ancillary ligand, both dinuclear iridium (III) complexes D-Ir-Caz and D-Ir-OXD exhibited a much lower luminescence quantum yields (ΦL) in comparison with their corresponding monomer complex Mono-Ir. Furthermore, the Mono-Ir-based device shows a EQE of 1.29% at 3.5 mA/cm2, while D-Ir-Caz- and D-Ir-OXD-based devices suffer relatively lower efficiencies of 0.27% and 0.41% accompanied with a negligible efficiency roll-off.183