Machine‐Learning‐Guided Discovery of Boron‐Free Narrowband Blue Thermally Activated Delayed Fluorescence Emitters

ABSTRACT Thermally activated delayed fluorescence (TADF) emitters enable color‐pure, energy‐efficient organic light‐emitting diodes (OLEDs), yet many ultra‐narrowband designs rely on synthetically demanding boron incorporation. Here we discover boron‐free emitters that reconcile a robust nitrogen‐only polycyclic scaffold, Rec. 2020‐grade pure‐blue emission, and small singlet–triplet gaps (Δ E ST ) conducive to TADF. We enumerated 19 518 13‐ring carbazole‐containing polycyclic aromatic hydrocarbons (Cz‐PAHs) and obtained quantum‐chemical reference values for ∼1000 molecules: emission energies and Δ E ST at S 1 ‐optimized geometries. A graph neural network enabled library‐wide prediction and revealed a pronounced negative correlation between emission energy and Δ E ST ( R = −0.75), implicating configuration mixing in S 1 and indicating that small‐gap candidates are enriched in the pure‐blue regime. Two selected Cz‐PAH emitters were synthesized and display deep‐blue, exceptionally narrow photoluminescence (full widths at half maximum 17–19 nm) with small experimental Δ E ST (0.13–0.19 eV). OLEDs incorporating these emitters deliver narrowband blue electroluminescence ( λ EL 456 and 481 nm); device A reaches chromaticity coordinates of (0.139, 0.069), close to the Rec. 2020 blue primary, whereas the sensitized device D achieves a maximum external quantum efficiency of 35.2%. Collectively, this work expands the boron‐free TADF design space and establishes an experimentally validated route to discovering high‐color‐purity organic emitters.