B─O‐Bond‐Mediated π‐Extension Enables Concurrent High Efficiency and Spectral Purity Toward BT.2020‐Standard Deep‐Blue MR‐TADF OLEDs

ABSTRACT Deep‐blue multi‐resonance thermally activated delayed fluorescence (MR‐TADF) emitters are crucial for next‐generation ultra‐high‐definition OLED displays, yet the concurrent realization of high color purity, high quantum efficiency, and a fast reverse intersystem crossing (RISC) rate remains elusive. Here, we present a B─O–bond‐mediated π‐extension design that harmonizes these conflicting performance metrics. In this approach, π‐extension effectively narrows the emission bandwidth and reduces the singlet–triplet energy gap (Δ E ST ), while the incorporation of B─O bond mitigates the bathochromic shift typically induced by π‐extension, thereby preserving high emission energy. The resulting doubly and triply borylated emitters, accessible via a lithium‐free one‐shot borylation on a gram scale, exhibit deep‐blue emissions with nearly BT.2020 chromaticity, close‐to‐unity quantum yields, and an order‐of‐magnitude enhancements in their RISC rate constants relative to the parent emitter. Correspondingly, the non‐sensitized OLEDs deliver maximum external quantum efficiencies (EQE max ) of up to 34.7%, blue index values of up to 394, and mitigated efficiency roll‐off. Meanwhile, in a more stable device configuration, LT 90 lifetimes (time to decay to 90% of the initial luminance) of up to 114.6 h at 500 cd m −2 are achieved. This work establishes a molecular design paradigm for constructing efficient, spectrally pure, and durable deep‐blue MR‐TADF emitters, advancing the pathway toward next‐generation display technologies.