Synthesis and properties of binaphthyl chiral thermally activated delayed fluorescence molecules using thioxanthone as acceptor

The currently reported axial chiral molecules based on the 3,3′-substitution of the binaphthyl skeleton are limited by intrinsic fluorescence properties, resulting in generally low device efficiencies (EQE < 5%) of related organic light emitting diodes (OLEDs). Herein, we designed and synthesized four pair of chiral binaphthyl enantiomers (R/S-1 − R/S-4) adopting acceptor-donor-donor-acceptor (ADDA) structure by introducing different thioxanthone modification groups on the 3,3′-position of 2,2′-dimethoxy-1,1′-binaphthalene. Among them, emitter R/S-2 and R/S-4 obtained by enhancing intramolecular charge transfer exhibited TADF characteristics due to relatively small ΔEST of 0.12 eV and 0.17 eV, and relatively moderate SOC matrix elements of 0.28 cm−1 and 0.10 cm−1 between the 1CT and 3LE states. The CD spectra of these enantiomers in diluted solutions showed perfect mirror images and reasonable gabs for small organic molecules (10−4–10−3). And the external quantum efficiencies (EQE) of 10.9% and 8.32% for device A and B based on emitter S-2 and S-4 were highest compared with currently reported axial chiral molecules based on the 3,3′-position substitution of binaphthyl skeleton, providing simple molecular design strategies to construct efficient CP-OLED device.