Unsymmetric Heteroleptic Ir(III) Complexes with 2-Phenylquinoline and Coumarin-Based Ligand Isomers for Tuning Character of Triplet Excited States and Achieving High Electroluminescent Efficiencies.

2-Phenylquinoline () and four coumarin-based ligand isomers with ease of synthesis have been selected to construct the unsymmetric heteroleptic [Ir(CN)(CN)(acac)]-type complex phosphors for organic light-emitting diodes (OLEDs). Six unsymmetric heteroleptic Ir(III) complexes have been obtained by employing four coumarin-based ligand isomers (///) in the [Ir(PQ)(CN)(acac)] structure due to two different coordinating carbon atoms in ligands and to form C-Ir bond. Through adopting unsymmetric heteroleptic [Ir(CN)(CN)(acac)] structure, these Ir(III) complexes can not only achieve impressive absolute quantum yield Φ (ca. 0.5-1.0), higher than that of complex [Ir(PQ)(acac)] (ca. 0.4), but also realize a dual modulation of both emission color from orange (, λ = 578 nm) to red (, λ = 622 nm) and the character of the lowest triplet excited states (T), showing both MLCT character and ILCT (intraligand charge transfer) character in their T states. , , and show MLCT character from Ir(III) center to ligand or and ILCT character in ligand or in their T states, while , , and show MLCT character from Ir(III) center to ligand and ILCT character in ligand in their T states. Moreover, the color-tuning mechanism and the lowest triplet state characters are investigated in detail. and were selected as emitters to evaluate the electroluminescent (EL) performance due to their high Φ of nearly up to unity. Optimal orange-emitting device based on can give a maximum external quantum efficiency (η) of 23.9%, a maximum current efficiency (η) of 70.9 cd A, and a maximum power efficiency (η) of 60.7 lm W. All these impressive results can definitely demonstrate the effectiveness of our simple approach for tuning character of the triplet excited states and achieving high-performance Ir-based phosphors in OLEDs.