C₁-Symmetric [Ir(C^N¹)(C^N²)(O^O)]-Tris-Heteroleptic Iridium(III)-Complexes with the Preferentially Horizontal Orientation for High-Performance Near-Infrared Organic Light-Emitting Diodes

The development of high-efficiency near-infrared (NIR)-emitting Ir(III)-complex-based phosphors for reliable NIR-OLEDs (near-infrared organic light-emitting diodes) is still a formidable challenge. Herein, a molecule-engineered approach is developed to afford three C₁-symmetric [Ir(C^N¹)(C^N²)(O^O)]-tris-heteroleptic Ir(III)-complexes ([Ir(iqbt)(dFppy)(acac)] (1), [Ir(iqbt)(ppy)(acac)] (2), and [Ir(iqbt)(dpqx)(acac)] (3)), whose good NIR-luminescent efficiency (Φ_PL = 0.18 for 1 (λ_em = 703 nm), 0.26 for 2 (λ_em = 715 nm) or 0.28 for 3 (λ_em = 707 nm)) originates from the strengthened ³MLCT contribution (MLCT = metal-to-ligand charge transfer). Moreover, the quantitative molecular orientation determination of their doped emitting layers (EMLs) reveals that the preferentially horizontal orientation of the emitting dipoles is beneficial to their highly efficient NIR-OLEDs with light out-coupling. Especially for the NIR-OLED -2 with λ_em = 715 nm, a high performance (η_EQE^Max = 5.30% and negligible (<2%) efficiency-roll-off) is realized among the reported solution-processed NIR-OLEDs based on Ir(III)-complexes at similar color gamut. This result shows that C₁-symmetric [Ir(C^N¹)(C^N²)(O^O)]-tris-heteroleptic Ir(III)-complexes can provide a new platform to low-cost and large-area scalable NIR-OLEDs.