Deep-blue organic light-emitting diodes for ultrahigh-definition displays

Multiple-resonance thermally activated delayed fluorescence materials have emerged as promising candidates for next-generation ultrahigh-definition displays due to their narrowband emission and triplet-harvesting capability. However, achieving optimal colour purity and device efficiency for blue multiple-resonance thermally activated delayed fluorescence emitters has presented challenges. Here we demonstrate an effective approach to attain superior deep-blue molecules by constructing twisted-boron-/nitrogen-/oxygen-embedded higher-order fused-ring frameworks with fully resonating structures. The optimized emitter exhibits high rigidity and minimized bonding/antibonding character for ultrasharp emission, along with a small singlet-triplet gap and large spin-orbit couplings for rapid spin flip. This combination results in deep-blue emission at 458 nm with a narrow full-width at half-maximum of 12 nm in solution and a reverse intersystem crossing rate constant of 2.29 x 106 s-1, on par with those of heavy-atom-based multiple-resonance thermally activated delayed fluorescence molecules. The related single-unit organic light-emitting diode achieves an external quantum efficiency of 39.2% with colour coordinates of (0.141, 0.050) and a narrow full-width at half-maximum of 14 nm. Furthermore, a two-unit stacked tandem hyperfluorescence organic light-emitting diode achieves an ultrahigh external quantum efficiency of 74.5% with low efficiency roll-off at high luminance values. This performance represents a remarkable balance between efficiency and colour purity in the deep-blue region, marking an important step towards power-efficient ultrawide-colour-gamut displays. Highly twisted multi-boron-based multiple-resonance thermally activated delayed fluorescence emitters enable deep-blue organic light-emitting diodes with high colour purity, a narrow full-width at half-maximum of 14 nm and a peak external quantum efficiency of 39.2%.