Circularly polarized organic light-emitting diodes with chiral asymmetric [Ir(C1^N1)(C2^N2)(L^X)]-tris-heteroleptic iridium(iii) complexes

Abstract

Circularly polarized luminescence (CPL) has great potential in the field of 3D display, not only in terms of energy utilization but also for the health of human eyes. The trinary heteroleptic Ir(III) complexes can achieve excellent photophysical properties through fine structural modifications of two different primary ligands and the ancillary ligand. Moreover, by introducing chiral groups into the main ligand, these complexes can also directly emit circularly polarized light. In this work, the first pair of chiral ternary heteroleptic Ir(III) complexes known to us, Δ/Λ-Ir(ppy)(S-pppy)(acac) (ppy: 2-phenylpyridine; S-pppy: (5S,7S)-5,6,6,7-tetramethyl-3-phenyl-5,6,7,8-tetrahydroisoquinoline; acac: acetylacetone), were designed and synthesized. Furthermore, in deoxygenated dichloromethane solution, Δ/Λ-Ir(ppy)(S-pppy)(acac) exhibited a maximum emission peak at 524 nm with a high photoluminescence quantum yield (PLQY) of 97% in 2,6-bis(3-(9H-carbazol-9-yl)phenyl)pyridine (26DCzPPy)-doped films (8 wt%) fabricated by evaporation. The enantiomers also showed strong CPL characteristics, with the luminescence dissymmetry factor |g_PL| of 1.92 × 10⁻³ in 8 wt% 26DCzPPy doped films. The organic light-emitting diodes (OLEDs) based on the isomers show a maximum external quantum efficiency (EQE_max) of 22.3% with strong and symmetrical CPEL signals. This novel approach for chiral Ir(III) complexes is highly promising for the future development of CP-OLEDs.