High-efficiency organic light-emitting diodes based on cationic iridium(iii) complexes with double tridentate ligands†

In order to improve the device performance of ionic Ir(III) complexes, multi dentate ligands were used to enhance the rigidity and stability of ionic Ir(III) complexes. Therefore, five cationic Ir(III) complexes with tridentate ligands were prepared. The decomposition temperatures (5% weight loss) of these complexes are between 290 and 441 °C. In polymethyl methacrylate films, these complexes show emission peaks between 488 and 537 nm with quantum efficiencies of 0.28–0.47. The density functional theory calculations indicate that the electron donating substituents on the cyclometalated benzene rings will reduce the proportion of Ir atoms in the frontier orbitals of these bis-tridentate Ir(III) complexes, thereby reducing their luminescence efficiency. Record-high device performance has been achieved with a superior external quantum efficiency over 17%, maximum brightness over 30 000 cd m⁻², and quite small efficiency roll-off. The device efficiencies of complexes with triptycene groups only slowly decrease until 6000 cd cm². These results demonstrate the great potential of ionic bis-tridentate Ir(III) complexes in state-of-the-art optoelectronic device applications.