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

The intrinsic helical π-conjugated skeleton makes helicenes highly promising for circularly polarized electroluminescence (CPEL). Generally, carbon helicenes undergo low external quantum efficiency (EQE), while the incorporation of a multi-resonance thermally activated delayed fluorescence (MR-TADF) BN structure has led to an improvement. However, the reported B,N-embedded helicenes all show low electroluminescence dissymmetry factors (g EL ), typically around 1×10 -3 . Therefore, the development of B,N-embedded helicenes with both a high EQE and g EL value is crucial for achieving highly efficient 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 with a maximum at 578 nm with a high luminescence dissymmetry factor (|g lum |) 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 an emitter show a maximum EQE of 35.5 %, a small full width at half-maximum of 48 nm, and, more importantly, a high |g EL | value of 6.2×10 -3 . The Q-factor (|EQE×g EL |) 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.