Efficient Circularly Polarized Electroluminescence from Chiral Thermally Activated Delayed Fluorescence Emitters Featuring Symmetrical and Rigid Coplanar Acceptors

Circularly polarized organic light-emitting diodes (CP-OLEDs) that enable circularly polarized luminescence (CPL) are promising for 3D display and photonic applications. However, the device efficiency and CPL character of CP-OLEDs still lag behind the practical requirements. Here, two pairs of axially chiral emitting enantiomers, flexible (R/S)-ODQPXZ and rigid (R/S)-ODPPXZ, are reported by fusing (R/S)-octahydro-binaphthol chiral source, diphenyl quinoxaline (DQ)/dibenzo[a,c]phenazine (DP) acceptors and phenoxazine (PXZ) donors. The symmetrical chiral-acceptor-donor configuration endows them thermally activated delayed fluorescence (TADF) properties with small singlet–triplet energy gaps of 0.16 and 0.07 eV, high photoluminescence quantum yields of 92% and 89% in doped films, and obvious mirror-image CPL characteristics, respectively. The CP-OLEDs based on these TADF enantiomers not only show a maximum external quantum efficiency of 28.3% with yellow emission for (R/S)-ODQPXZ and 20.3% with orange-red emission for (R/S)-ODPPXZ, but also display the CPL with dissymmetry factors (g_EL) of 6.0 × 10⁻⁴ and 2.4 × 10⁻³, respectively. The high efficiency and obvious CPL of (R)-ODPPXZ arise from a synergetic interplay of the TADF skeleton and the rigid coplanar acceptor for efficient chiral induction and suppressed intramolecular rotational quenching.