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 x 10(-4) and 2.4 x 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.

Automated summary

This study reports two pairs of axially chiral emitting enantiomers with flexible and rigid structures, exhibiting thermally activated delayed fluorescence properties and obvious mirror-image circularly polarized luminescence characteristics. The CP-OLEDs based on these enantiomers demonstrate high efficiency and significant CPL effects.