Pyridinylphosphorothioate-based blue iridium(iii) complex with double chiral centers for circularly polarized electroluminescence

Abstract

Circularly polarized organic light-emitting diodes (CP-OLEDs) have received considerable attention due to their promising applications in 3D displays. However, up to now, CP-OLEDs using iridium(III) phosphors as emissive dopants exhibited low brightness, insufficient efficiency, serious efficiency roll-off, and especially low electroluminescence dissymmetry factors (g_EL). In this study, a blue Ir(III) complex Ir(dfppy)₂(sdpp) (dfppy is 2-(2,4-difluorophenyl)pyridine, sdpp is pyridinylphosphorothioate) peaking at 466 nm was synthesized, and two pairs of enantiomers containing the λ or δ isomer together with a chiral phosphine center (R or S) were separated into λ-Ir(dfppy)₂(S-sdpp), δ-Ir(dfppy)₂(R-sdpp), λ-Ir(dfppy)₂(R-sdpp) and δ-Ir(dfppy)₂(S-sdpp), respectively. It is the first example to investigate phosphine chirality in an Ir(III) complex, and the electron cloud distribution in the chiral conjugated ancillary ligand and λ/δ chirality of the Ir(III) center induced Ir(dfppy)₂(sdpp) to exhibit decent circularly polarized luminescence (CPL) activities with a dissymmetry factor (|g_PL|) around 1.4 × 10⁻³. The OLEDs based on Ir(dfppy)₂(sdpp) exhibited a maximum external quantum efficiency of 13.8% with mild efficiency roll-off. Notably, the CP-OLEDs based on λ-Ir(dfppy)₂(S-sdpp), δ-Ir(dfppy)₂(R-sdpp), λ-Ir(dfppy)₂(R-sdpp) and δ-Ir(dfppy)₂(S-sdpp) showed obvious circularly polarized electroluminescence (CPEL) signals with a g_EL of −2.1 × 10⁻³, 2.4 × 10⁻³, −2.1 × 10⁻³ and 1.9 × 10⁻³, respectively, thus affording an efficient strategy for the design of chiral blue Ir(III) emitters and their CP-OLEDs.