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

ABSTRACT 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 (LT 95 ≈ 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.