Blue Axially Chiral Biphenyl Based Thermally Activated Delayed Fluorescence Materials for Efficient Circularly Polarized OLEDs

Abstract

Abstract This work presents two axial chiral biphenyl based blue thermally activated delayed fluorescence materials (M‐BPCZ4 and P‐BPCZ4) with four carbazole (CZ) donors and two cyano (CN) acceptors. The rigid CZ‐CN based molecular structures with multiple chromophores result in small gaps among charge transfer states (CTs), and the spin−orbit coupling between CT and locally excited states pushes the reverse intersystem crossing (RISC) process. Besides, this chiral luminescence center strategy with the close distance between chiral units and chiral luminescence region contributes to satisfying circularly polarized luminescence properties with dissymmetry factor | g PL | of 5.0 × 10 −3 for ( R/S )‐M‐BPCZ4 and 4.7 × 10 −3 for ( R/S )‐P‐BPCZ4 enantiomers, respectively. Furthermore, the positions of other two CZ units have great effects on the racemization temperatures and circularly polarized electroluminescence properties of the enantiomers. The chiral dyes doped circularly polarized organic light‐emitting diodes compatibly display good performances with external quantum efficiency of 18.3% with slight efficiency roll‐off and high electroluminescence | g EL | of 5.5 × 10 −3 .