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Origin of rare and highly efficient phosphorescent and electroluminescent iridium(III) complexes based on C--N=N
Xiao-Na Li1, Zhi-Jian Wu, Xiao-Juan Liu
1State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, People's Republic of China.
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.
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