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.

Donor-σ-Acceptor Molecules for Green Thermally Activated Delayed Fluorescence by Spatially Approaching Spiro Conformation.

By separating donor/acceptor with a σ linker while keeping them in contact through space interactions, new oxygen-bridged triphenylamine/fluorene-based donor-σ-acceptor (D-σ-A) type thermally activated delayed fluorescence (TADF) emitters are developed. X-ray structural analyses and time-dependent density functional theory reveal that tilted configuration of spiro skeleton, extended delocalization of the highest occupied molecular orbital (HOMO), and lowest triplet state of charge transfer property (3CT) play key roles in the TADF mechanism. OLEDs fabricated with these D-σ-A emitters achieved good external quantum efficiency of 20.4% and long operating durability of 18000 h at 100 cd m-2.