Abstract
<p><meta charset="UTF-8" />Multiple resonance thermally activated delayed fluorescence (MR-TADF) emitters hold promise for efficient organic light-emitting diodes (OLEDs) and wide gamut displays. An azepine donor is introduced into the boron–nitrogen system for the first time. The highly twisted conformation of a seven-ring embedded new molecule, <strong>TAzBN</strong>, increases the intermolecular distances, suppressing self-aggregation emission quenching. Meanwhile, the azepine donor is crucial to achieve a narrow singlet-triplet gap (0.03 eV) as well as boost the reverse intersystem crossing (RISC) rate to 8.50 × 10<small><sup>5</sup></small> s<small><sup>−1</sup></small>. It is noteworthy that <strong>TAzBN</strong> demonstrates an impressive photoluminescence quantum yield of 94%. In addition, its nonsensitized OLED displayed a remarkable external quantum efficiency (EQE<small><sub>max</sub></small>) with values peaking at 27.3%, and an EQE of 21.4% at 500 cd m<small><sup>−2</sup></small>. This finding shows that when <strong>TAzBN</strong> is used at a high concentration of 10 wt%, its device maintains efficiency even at higher brightness levels, highlighting <strong>TAzBN</strong>'s resistance to aggregation quenching. Furthermore, <strong>TAzBN</strong> enantiomers showed circularly polarized photoluminescence characteristics with dissymmetry factors |<em>g</em><small><sub>PL</sub></small>| of up to 1.07 × 10<small><sup>−3</sup></small> in doped films. The curved heptagonal geometry opens an avenue to design the MR-TADF emitters with fast spin-flip and chiroptical properties.</p>