Efficient and Stable\nNarrowband Pure-Red Light-Emitting\nDiodes with Electroluminescence Efficiencies Exceeding 43%

Advanced multiresonance-induced thermally activated delayed\nfluorescence\n(MR-TADF) materials exhibit exceptional promise for applications in\nstate-of-the-art organic light-emitting diodes (OLEDs) owing to their\nunique narrowband emissions and high luminescent efficiencies. Despite\nsubstantial progress with blue and green MR-TADF materials, the development\nof pure-red MR-TADF emitters has lagged behind, thereby hindering\nthe advancement toward high-performance ultrahigh-definition OLED\ndisplays. Here, we propose an effective approach for designing pure-red\nMR-TADF molecules based on the integration of secondary electron-donating\nunits and π-skeleton extension into MR cores, which enables\nnot only a redshift of narrowband emission but also an acceleration\nof reverse intersystem crossing (RISC) rate. The proof-of-the-concept\nemitter BNTPA showcases a bright and saturated red emission centered\nat 613 nm with a full-width at half-maximum of 0.14 eV, together with\na more than twofold increase in the RISC rate. As a result, TADF OLEDs\nbased on BNTPA achieved a record maximum external quantum efficiency\n(EQ<i>E</i><sub>max</sub>) of up to 35.2% with Commission\nInternationale de l’Eclairage (CIE) coordinates of (0.657,\n0.343), approaching the coordinates of the National Television Standards\nCommittee (NTSC) red standard. Moreover, phosphor-assisted fluorescence\ndevices exploiting BNTPA as a terminal emitter exhibit an exceptional\nEQ<i>E</i><sub>max</sub> of 43.3%, accompanied by improved\noperational stability.