B,N-Embedded Hetero[9]Helicene-Induced Chiral Assemblies for Amplified Circularly Polarized Electroluminescence

Circularly polarized organic light-emitting diodes (CP-OLEDs) based on B,N-embedded heterohelicenes are promising due to their narrowband emission and high electroluminescence efficiency, yet their development has been hindered by intrinsically weak circularly polarized electroluminescence (CPEL) with dissymmetry factor (g_EL) typically only 10^-3, which falls far short of the theoretical limit (±2). Herein, we overcome this limitation via a co-assembly strategy employing B,N-embedded hetero[9]helicene (BN9H) as a dual-role component. Possessing both a chiral scaffold and multi-resonance thermally activated delayed fluorescence (MR-TADF), BN9H is co-assembled with luminescent nematic liquid crystal (PFQ). In this assembly, BN9H acts not only as a chiral inducer, driving the achiral PFQ host into a long-range ordered chiral nematic superstructure, but also as an efficient energy acceptor. The co-assemblies exhibit narrowband emission (FWHM [full width at half maximum] = 34 nm) and a dramatically amplified |g_lum| of 0.18 which nearly two orders of magnitude higher than BN9H itself. Corresponding CP-OLEDs based on those chiral assemblies achieve excellent integrated performance: narrowband green electroluminescence (FWHM = 33 nm), EQE_max of 4.6%, and high |g_EL| of up to 0.11. This work breaks the long-standing |g_EL| bottleneck for chiral MR-TADF molecules and establishes a new paradigm for developing high-performance CPEL devices with balanced efficiency, color purity, and strong chiroptical activity.