Chlorine‐Enabled Double Borylation Strategy for π‐Extended MR‐TADF Emitters: From Synthetic Challenge to Benchmark OLEDs

Abstract Thermally activated delayed fluorescence (TADF) materials are promising emitters for organic light‐emitting diodes (OLEDs) owing to their ability to harvest both singlet and triplet excitons. However, realizing pure‐green, narrowband emission with simultaneously high efficiency and stability remains a long‐standing challenge for display applications. In this study, we report a concise one‐shot double borylation strategy uniquely enabled by chlorine substituents acting as both directing and functional groups. This dual role not only ensures regioselective synthesis of a π‐extended multiple resonance (MR) framework—previously considered synthetically inaccessible—but also provides versatile handles for late‐stage diversification. The resulting key intermediate, W‐DABNA‐Cl , was obtained in 48% yield and readily converted into a series of structurally diverse MR‐TADF emitters through single‐step derivatizations. These emitters exhibited narrowband emissions from deep green to yellow‐green (FWHM 27–34 nm) with tunable photophysical properties. Notably, TADF‐sensitized fluorescence devices based on W‐DABNA‐Cz achieved an excellent maximum external quantum efficiency (EQE) of 36.1%. More importantly, the device maintained record‐high efficiencies of 34.3% and 29.5% at luminance levels of 1000 and 10 000 cd m −2 , respectively, representing the best efficiency–brightness trade‐off among reported green sensitized OLEDs. This work not only overcomes synthetic bottlenecks in accessing π‐extended MR‐TADF frameworks but also establishes a versatile platform for color‐tunable, high‐performance OLEDs.