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∣ ≈ 1.4×10−3 and 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 3.6×10−3 with decreased device EQEmax of 15.4%. By further replacing benzonitrile with (trifluoromethyl)pyridine, the enantiomers of (R/S)-SCFPY show similar ∣gPL∣ factors of 3.5×10−3 and device EQEmax up 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 gEL factors of −1.4/1.8×10−3, −3.6/3.6 ×10−3 and −3.7/3.6×10−3, respectively. These results indecate by delicate functional group engineering, high g factor can be achieved while maintaining decent device performances. Besides, (R/S)-SCFPY represents an impressive TADF emitter, which shows promoted g factor and recorded high device EQEmax among similar molecules.