Highly efficient circularly polarized phosphorescent electroluminescence from iridium(iii) complexes with chiral ligands

Abstract

A pair of chiral iridium(III) complexes with only ligand chiral centers were successfully synthesized. Strong intramolecular hydrogen bonds exist in these complexes, which improve their stability and luminescence efficiency. All complexes exhibited good thermal stability with T_d > 396 °C and nearly unitary PLQYs. The HOMOs of these complexes are mostly located on the chiral auxiliary ligands with a proportion exceeding 62%, which can improve their chiral induction ability. Therefore, their CD spectra display perfect mirror symmetry, and their PL spectra also have apparent circular polarization with dissymmetry factors on the order of 10⁻³. The circularly polarized organic light-emitting diodes using these chiral emitters exhibit excellent performances with a maximum external quantum efficiency (EQE_max) of 31.9% and intense circularly polarized electroluminescence signals with a dissymmetry factor (|g_EL|) of up to 3.0 × 10⁻³. This article proposes a simple material design strategy that takes into account both electroluminescence efficiency and asymmetry factors.