Efficient circularly polarized photoluminescence and electroluminescence of chiral spiro-skeleton based thermally activated delayed fluorescence molecules

Chiral thermally activated delayed fluorescence (TADF) molecules showing circularly polarized luminescence (CPL) have great potential in 3D displays. However, the relationships among CPL property, device performance and molecule structure are still not clear. In this article, we develop a strategy to promote dissymmetry factors without sacrifice in device performance and study the impact of molecule structures towards CPL property. Three novel TADF enantiomers are synthesized and studied. (R/S)-SCN with diminutive cyano group as an acceptor shows dissymmetry factor ∣gPL∣ ≈ 1.4×10−3and noticeable organic light-emitting diode (OLED) performances with a maximum external quantum efficiency (EQEmax) of 23.0%. For (R/S)-SPHCN, the prolonged electron withdrawing group benzonitrile enhances ∣gPL∣ up to 3.6×10−3with decreased device EQEmaxof 15.4%. By further replacing benzonitrile with (trifluoromethyl)pyridine, the enantiomers of (R/S)-SCFPY show similar ∣gPL∣ factors of 3.5×10−3and device EQEmaxup to 23.3%, which represents the highest efficiency among sprio-type TADF materials based OLEDs. Furthermore, the OLEDs also show obvious circularly polarized electroluminescence with gELfactors of −1.4/1.8×10−3, −3.6/3.6 ×10−3and −3.7/3.6×10−3, respectively. These results indecate by delicate functional group engineering, high gfactor can be achieved while maintaining decent device performances. Besides, (R/S)-SCFPY represents an impressive TADF emitter, which shows promoted gfactor and recorded high device EQEmaxamong similar molecules.