B,N‐Embedded Hetero[9]helicene Toward Highly Efficient Circularly Polarized Electroluminescence

The intrinsic helical p‐conjugated skeleton makes helicenes highly promising for circularly polarized electroluminescence (CPEL). Generally, carbon helicenes undergo low external quantum efficiency (EQE), while the incorporation of multi‐resonance thermally activated delayed fluorescence (MR‐TADF) BN structure has achieved an improvement. However, the reported B,N‐embedded helicenes all show low electroluminescence dissymmetry factors (gEL) typically hovering around 1 × 10‐3. Therefore, the development of B,N‐embedded helicenes with both high EQE and gEL value is crucial for achieving highly efficiency CPEL. Herein, a facile approach to synthesize B,N‐embedded hetero[9]helicenes, BN[9]H, is presented. BN[9]H shows a bright photoluminescence peaking at 578 nm with high luminescence dissymmetry factor (|glum|) up to 5.8 × 10‐3, attributed to its inherited MR‐TADF property and intrinsic helical skeleton. Furthermore, circularly polarized OLED devices incorporating BN[9]H as emitter show maximum EQE of 35.5%, a small full width at half‐maximum of 48 nm, and more importantly, a high |gEL| of 6.2 × 10‐3. The Q‐factor (|EQE × gEL|) of CP‐OLEDs is determined to be 2.2 × 10‐3, which is the highest among helicene analogues. This work provides a new approach for the synthesis of higher helicenes and paves a new way for the construction of highly efficient CPEL materials.