Stable Enantiomers Displaying Thermally Activated Delayed Fluorescence: Efficient OLEDs with Circularly Polarized Electroluminescence.

Aromatic-imide-based thermally activated delayed fluorescent (TADF) enantiomers, (+)-(S,S)-CAI-Cz and (-)-(R,R)-CAI-Cz, were efficiently synthesized by introducing a chiral 1,2-diaminocyclohexane to the achiral TADF unit. The TADF enantiomers exhibited high PLQYs of up to 98 %, small ΔEST  values of 0.06 eV, as well as obvious temperature-dependent transient PL spectra, thus demonstrating their excellent TADF properties. Moreover, the TADF enantiomers showed mirror-image CD and CPL activities. Notably, the CP-OLEDs with CPEL properties based on the TADF enantiomers not only achieved high EQE values of up to 19.7 and 19.8 %, but also displayed opposite CPEL signals with gEL  values of -1.7×10-3 and 2.3×10-3 , which represents the first CP-OLEDs, based on the enantiomerically pure TADF materials, having both high efficiencies and intense CPEL.