Stable Enantiomers Displaying Thermally Activated Delayed Fluorescence: Efficient OLEDs with Circularly Polarized Electroluminescence
Meng Li,a Si-Hua Li,b Dongdong Zhang,c Minghan Cai,c Lian Duan,c Man-Keung Fung,*b Chuan-Feng Chen*a
a. CAS Key Laboratory of Molecular Recognition and Function Institute of Chemistry, Chinese Academy of Sciences Beijing 100190, China and University of Chinese Academy of Sciences, Beijing 100049, China.
b. Institute of Functional Nano & Soft Materials Soochow University Suzhou, Jiangsu 215123, China
c. Department of Chemistry, Tsinghua University Beijing 100084, China
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.