Record‐High Performance Hyperfluorescent OLEDs Achieved via Electronic Structure Control of Chlorine‐Diversified MR‐TADF Emitters

Multiple-resonance (MR)-type thermally activated delayed fluorescence (TADF) emitters enable highly efficient and narrowband organic light-emitting diodes (OLEDs), yet their electronic tunability has remained limited. Here, we demonstrate that chlorine-enabled late-stage diversification of the MR scaffold ω-DABNA allows systematic control of ionization potential and electron affinity, leading to record-high performance in hyperfluorescent (HF) OLEDs. Three derivatives, ω-DABNA-4TBP, ω-DABNA-4CzP, and ω-DABNA-4CNP, were synthesized via a single-step Suzuki-Miyaura coupling, exhibiting narrowband green emission (FWHM = 23-26 nm) and remarkably high horizontal orientation (Θ_h = 85%-87%). Among them, ω-DABNA-4TBP achieved an external quantum efficiency (EQE_max) of 36.1% and maintained 33.2% at 1000 cd m^-2, together with outstanding operational stability (LT₉₅ ≈ 385 h). This performance represents one of the highest ever reported for HF-OLEDs. The other derivatives exhibited comparable efficiencies but much shorter lifetimes, revealing that subtle modulation of electronic structure critically governs exciton dynamics and device durability. This study establishes chlorine-guided electronic structure control as a versatile platform for developing next-generation MR-TADF emitters combining narrowband emission, record-high efficiency, and long-term operational stability.