An Ortho -B−π–B-Fused All-Six-Membered BN[7]Helicene for Narrowband Circularly Polarized Luminescence with Robust Configurational Stability

Abstract

Circularly polarized organic light-emitting diodes (CP-OLEDs) directly generate circularly polarized electroluminescence (CPEL), enabling high-quality optical output with reduced reliance on external polarizing components for advanced display technologies and emerging chiral optoelectronic applications. Helicene-based circularly polarized multiple resonance thermally activated delayed fluorescence (CP-MR-TADF) emitters combine intrinsic chirality with narrowband emission, but extending their emission to longer wavelengths is often accompanied by significant spectral broadening and a loss of configurational stability. Here, we introduce a BN[7]helicene framework that addresses these issues. Using an ortho-B−π–B topology, we construct an all-six-membered-ring-fused structure whose enantiomeric solid powders retain configurational stability and CPL performance after continuous heating at 250 °C for 6 days. The enantiomers ( P / M )-DBN- cp ICz exhibit yellow emission at 558 nm with a full-width at half-maximum (FWHM) of 23 nm, photoluminescence dissymmetry factors of +2.2/–1.9 × 10–3 and an energy barrier of racemization of 48.28 kcal mol–1. CP-OLEDs based on ( P / M )-DBN- cp ICz achieve narrowband CPEL at 572 nm, with FWHM’s of 29–30 nm and dissymmetry factors of +2.1/–2.3 × 10–3. This work establishes a viable route toward long-wavelength, high-color-purity circularly polarized luminescence with enhanced configurational stability for robust chiral MR optoelectronic materials.