C-1-Symmetric [Ir(C boolean AND N-1)(C boolean AND N-2)(N boolean AND O)]-tris-heteroleptic Ir(III)-complexes with a horizontal orientation for efficient near-infrared (NIR) polymer light-emitting diodes (PLEDs)

摘要

Using conventional fac-[Ir(C boolean AND N)(3)]-homoleptic or [Ir(C boolean AND N)(2)(L boolean AND X)]-bis-heteroleptic iridium(III)-complexes with NIR-phosphorescence (NIR = near infrared) as dopants, the realization of reliable NIR-OLEDs/PLEDs (organic/polymer light-emitting diodes) with high performance remains a real challenge. In this study, taking Hqibt (1-(benzo[b]-thiophen-2-yl)-isoquinoline) as the HC boolean AND N-1 ligand, Hppy (phenyl-4-yl)pyridine) as the HC boolean AND N-2 ligand and Br-Hpic (5-Br-picolinic acid) or Hpic (picolinic acid) as the N boolean AND O-ancillary, two novel C-1-symmetric [Ir(C boolean AND N-1)(C boolean AND N-2)(N boolean AND O)]-tris-heteroleptic iridium(III)-complexes [Ir(iqbt)(ppy)(pic)] (1) and [Ir(iqbt)(ppy)(Br-pic)] (2) are molecularly designed, respectively, where large TDM (transition dipole moment) and strengthened (MLCT)-M-3 (metal-to-ligand charge transfer) effects are established to afford their good NIR-phosphorescent efficiency (phi(PL) = 0.27 for 1 (lambda(em) = 698 nm); 0.21 for 2 (lambda(em) = 696 nm)). Moreover, in their doped EMLs (emitting layers), a preferentially horizontal orientation of the TDMs is promoted, due to which, the NIR-PLEDs-1-2 exhibit an attractively high efficiency (eta(max)(EQE) = 3.1-4.7%; lambda(em) = 698 nm) as well as an almost negligible (<5%) efficiency roll-off. This finding means the C-1-symmetric [Ir(C boolean AND N-1)(C boolean AND N-2)(N boolean AND O)]-tris-heteroleptic Ir(III)-complexes show potential as low-cost, large-area and scalable NIR-PLEDs.