Strong luminescent iridium complexes with C∧N-N structure in ligands and their potential in efficient and thermally stable phosphorescent OLEDs

A new Ir complex with the ligand 1,4-bis(phenyl)phthalazine (BPPa) resembling sp ²-hybrid N adjacent to the chelating N atom was developed. The complexes were also studied for their potential in efficient and thermally stable phosphorescent organic light emitting diodes (OLED). The structure of Ir complex shows that the molecule has octahedral geometry, with three BPPa ligands cyclometalated to the central iridium atom. The only difference between the molecular structures of Ir(PPy) ₃ and Ir(PPya) ₃ arises from the atom adjacent to the chelating N in the ligand. Ir(BPPa) ₃ emits a red light peaked at 625 nm in a CH ₂Cl ₂ solution, with a PL quantum yield of 0.20 measured with Rhodamine B as a calibrations standard. The devices with 2, 5, and 10% of Ir(BPPa) ₃ show maximum external quantum efficiencies (EQE) of 4.0, 8.3, and 5.1%.