Circularly Polarized MR‐TADF Emitters with an Asymmetric Spiro‐Carbon‐Locking Architecture for Concentration‐Quenching‐Resistant Narrowband Circularly Polarized Electroluminescence

Highly efficient circularly polarized luminescence (CPL) emitters with narrowband emission are promising for ultra-high-definition (UHD) and three-dimensional (3D) displays. Herein, we put forward an "asymmetric spiro-carbon-locking architecture" strategy to construct chiral multiple resonance thermally activated delayed fluorescence (MR-TADF) emitters. Two pairs of enantiomers, (R/S)-BN-FLCz and (R/S)-BN-FLTPA, are successfully achieved, which show high photoluminescence quantum yields exceeding 95%, narrow full-width at half-maximums (FWHMs) of 24-26 nm (0.11-0.12 eV) and 26-27 nm (0.12 eV) in films over a wide range of dopant concentrations (1-30 wt%), and obvious mirror-image CPL properties in both solution and film states. As a result, the sensitizer-free organic light-emitting diodes (OLEDs) based on BN-FLCz and BN-FLTPA exhibit pure green emission with the FWHMs of 26 nm (0.12 eV) and 27 nm (0.13 eV), Commission International de l'Eclairage (CIE) coordinates of (0.16, 0.72) and (0.18, 0.73), and the record-breaking maximum external quantum efficiencies (EQE_maxs) of 37.9% and 39.8%, respectively. Even at the high doping concentration of 30 wt%, the EQE_maxs for BN-FLCz and BN-FLTPA remain at 35.5% and 36.6% without sacrificing the color fidelity. Furthermore, the circularly polarized organic light-emitting diodes (CP-OLEDs) with (R/S)-BN-FLCz and (R/S)-BN-FLTPA displayed clear circularly polarized electroluminescence (CPEL) signals with electroluminescence dissymmetry factors (g_EL) of +0.85/-1.19 × 10^-3 and +0.84/-1.22 × 10^-3, respectively.