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

Abstract

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 (ΦPL = 0.18 for 1 (λem = 703 nm), 0.26 for 2 (λem = 715 nm) or 0.28 for 3 (λem = 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 λem = 715 nm, a high performance (ηEQEᴹᵃˣ = 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 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.