B‐N Covalent Bond Embedded Double Hetero‐[n]helicenes for Pure Red Narrowband Circularly Polarized Electroluminescence with High Efficiency and Stability

Abstract

AbstractChiral B/N embedded multi‐resonance (MR) emitters open a new paradigm of circularly polarized (CP) organic light‐emitting diodes (OLEDs) owing to their unique narrowband spectra. However, pure‐red CP‐MR emitters and devices remain exclusive in literature. Herein, by introducing a B‐N covalent bond to lower the electron‐withdrawing ability of the para‐positioned B‐π‐B motif, the first pair of pure‐red double hetero‐[n]helicenes (n = 6 and 7) CP‐MR emitter peaking 617 nm with a small full‐width at half‐maximum of 38 nm and a high photoluminescence quantum yield of ≈100% in toluene is developed. The intense mirror‐image CP light produced by the enantiomers is characterized by high photoluminescence dissymmetry factors (gPL) of +1.40/−1.41 × 10−3 from their stable helicenes configuration. The corresponding devices using these enantiomers afford impressive CP electroluminescence dissymmetry factors (gEL) of +1.91/−1.77 × 10−3, maximum external quantum efficiencies of 36.6%/34.4% and Commission Internationale de I’Éclairage coordinates of (0.67, 0.33), exactly satisfying the red‐color requirement specified by National Television Standards Committee (NTSC) standard. Notably a remarkable long LT95 (operational time to 95% of the initial luminance) of ≈400 h at an initial brightness of 10,000 cd m−2 is also observed for the same device, representing the most stable CP‐OLED up to date.