title: Origin of rare and highly efficient phosphorescent and electroluminescent iridium(III) complexes based on C--N=N ligands, a theoretical explanation.
abstract: The origin of the rare and highly strong phosphorescent (PL) and electroluminescent (EL) Ir(III) complexes with C--N=N ligand, tris[3,6-bis(phenyl)pyridazinato-N(1),C(2)]iridium (Ir(BPPya)(3)) (1), tris[1,4-bis(phenyl)phthalazine]iridium (Ir(BPPa)(3)) (2), and tris[1-(2,6-dimethylphenoxy)-4-(4-chlorophenyl)phthalazine]iridium ((Ir(MPCPPZ)(3)) (3) are investigated theoretically. By changing the conjugation length of the C--N=N ligand from BPPya to BPPa, one can tune the emission color from green in 1 to saturated red in 2. The addition of sterically bulky phenolic substituents in 3 exhibits the highest external quantum efficiency of 20.2% ph el(-1) and luminescence efficiency of 18.4 cd A(-1). Density functional theory (DFT) and time-dependent DFT (TDDFT) methods are used to rationalize these properties. The more promising PL and EL properties of 3 result from the bulky phenolic group, which acts as a pendant at the periphery of the emitting core and protects the emitting core from the hazardous intermolecular interaction of emitters and reduces luminescence quenching.
authors.affiliation: State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, People's Republic of China.
authors.forename: Xiao-Na
authors.initials: XN
authors.lastname: Li
authors.forename: Zhi-Jian
authors.initials: ZJ
authors.lastname: Wu
authors.forename: Xiao-Juan
authors.initials: XJ
authors.lastname: Liu
authors.forename: Hong-Jie
authors.initials: HJ
authors.lastname: Zhang