Circularly Polarized Electroluminescence from Intrinsically Axial Chiral Materials Based on Bidibenzo[b,d]furan/bidibenzo[b,d]thiophene

Abstract Herein, by connecting chiral bidibenzo[b,d]furan/bidibenzo[b,d]thiophene and multi‐resonance thermally activated delayed fluorescence (MR‐TADF) units, two pairs of intrinsically axial chiral MR‐TADF materials (R/S‐BDBF‐BNO and R/S‐BDBT‐BNO) realize mirror‐symmetric circularly polarized luminescence (CPL) and narrowband emission. The chiral moieties effectively engage in frontier molecular orbital distributions through the establishment of covalent bonds with boron atoms. The proportions of (1,1′‐bidibenzo[b,d]furan)‐2,2′‐diol in the highest occupied and lowest unoccupied natural transition orbitals (HONTO/LUNTO) are 25.3% and 64.7%, respectively. In addition, BDBT‐BNO processes a dual‐channel transition mode, thus the (1,1′‐bidibenzo[b,d]thiophene)‐2,2′‐diol constitutes 22.8%, 24.3% and 54.0%, 46.9% of the distributions of HONTO, HONTO‐1 and LUNTO, LUNTO+1, respectively. The high proportions endow R/S‐BDBF‐BNO and R/S‐BDBT‐BNO with good CPL properties with dissymmetry factors (|g_PL|) of 1.7/1.8 × 10⁻³. Correspondingly, the circularly polarized organic light‐emitting diodes based on the enantiomers exhibit mirror symmetrical circularly polarized electroluminescence with |g_EL| factors of 1.5/1.6 × 10⁻³. Furthermore, the introduction of sulphur atoms enables BDBT‐BNO to have a high maximum external quantum efficiency of 35.7% in device.