Aza‐Heptagon Heterocycle Embedded B,N‐Hetero[8]Helicene Toward Efficient Narrowband Circularly Polarized Electroluminescence

Abstract Helicene‐based emitters for high‐efficiency circularly polarized organic light‐emitting diodes (CP‐OLEDs) still present several unresolved challenges of suboptimal color purity in higher‐ordered helicenes and serious efficiency roll‐off. Herein, a pair of chiral [8]helicenes ( P/M ‐ BN8H ) are successfully constructed by fusing B,N‐embedded polycyclic aromatic hydrocarbon with carbazole and indolocarbazole units via an aza‐heptagon heterocycle. The strategy of incorporating twisted heterocycles effectively modulates both the electronic structure and geometric configuration of the helicene backbone. This approach simultaneously suppresses intermolecular interactions while preserves the intrinsic multiple resonance thermally activated delayed fluorescence characteristics of the target molecule. Moreover, the presense of aza‐heptagon heterocycle promotes spin‐orbit coupling between the locally excited triplet states and the simple state, facilitating the reverse intersystem crossing process thereby suppressing efficiency roll‐off. Furthermore, the π‐extended [8]helicene conjugation structure effectively stabilizes the chiral configuration, enabling helical enantiomer robust circularly polarized luminescence properties. The CP‐OLEDs fabricated with P / M ‐ BN8H achieved narrowband emission with a small full width at half maximum of 37 nm and a maximum external quantum efficiency of up to 30.0% with low efficiency roll‐off, and also demonstrated significant circularly polarized electroluminescence signals.