Indolocarbazole Fused B,N‐Embedded [9]Helicene Exhibiting Fast Reverse Intersystem Crossing for Efficient Circularly Polarized Electroluminescence

Abstract Recently, B,N‐embedded helicenes have emerged as promising candidates for high‐performance circularly polarized electroluminescence (CPEL). However, their intrinsically long delayed fluorescence lifetimes and slow reverse intersystem crossing (RISC) severely limit exciton utilization, resulting in serious efficiency roll‐off under high current density. To address this issue, an indolocarbazole fused B,N‐embedded [9]helicene ( IBN9H ) is designed and synthesized. It is found that IBN9H showed significantly accelerated RISC process and suppressed triplet exciton accumulation. Consequently, IBN9H exhibits intense emission at 526 nm with full width at half maximum (FWHM) of 0.11 eV, a short delayed fluorescence lifetime of 7.2 µs, and a high RISC rate of 3.96 × 10 5 s −1 , which represents the highest among reported B,N‐embedded helicenes. Notably, CP‐OLEDs based on IBN9H shows a maximum external quantum efficiency (EQE max ) of 33.5% with low efficiency roll‐off (EQE > 24.0% at 10,000 cd m − 2 ), a maximum luminance over 100,000 cd m − 2 , and intense CPEL with | g EL | of 2.7 × 10 −3 . This work presents a rational molecular design strategy to reduce the efficiency roll‐off in B,N‐embedded helicenes, and provides a promising CPEL material with excellent overall performances.