Synthesis, characterization and electroluminescence properties of iridium complexes based on pyridazine and phthalazine derivatives with C^NN structure

We reported the synthesis and characterization of three novel tris-cyclometalated iridium(III) complexes with pyridazine and phthalazine derivatives as ligands bearing C^NN structure, namely, Ir(PYA)3, Ir(PHB)3, and Ir(PHC)3. Reactions of the ligands with IrCl3·3H2O directly afforded tris-cyclometalated iridium(III) complexes in 31–39% yields. X-ray analysis revealed that the complexes exhibited the facial configuration, and the Ir–C bond lengths of the complexes are 2.009(3), 2.013(3), 2.019(3) Å for Ir(PYA)3, and 1.993(4), 2.002(4), 2.004(4) Å for Ir(PHB)3, respectively. The iridium complexes-based OLEDs fabricated by spin-coating technique exhibited promising performance. At 4 wt% doping level and a practical luminance of 100 cd m−2, the external quantum efficiencies of the devices using Ir(PYA)3, Ir(PHB)3 and Ir(PHC)3 as dopants reached 9.0, 6.9 and 9.3% photons/electron, respectively.