Negatively Curved Diaza-Octagon Heterocycle Fused with Polycyclic Aromatic Hydrocarbons for Ultra-Narrowband Deep-Blue Emission.

Developing new polycyclic aromatic hydrocarbons (PAHs) skeletons with narrowband emission is crucial for advancing ultra-high-definition displays. Inspired by the aesthetic configuration of negatively curved octagonal rings and the multiple resonance (MR) effect, we designed a novel diaza-octagon heterocycle fused with PAHs, abbreviated as 8NN, and its phenyl-substituted derivative 8NNP. Crystal data and theoretical calculations show that their peripheral PAHs exhibit significant rigidity, while the internal diaza-octagon ring confers skeleton flexibility and flipping properties. Notably, owing to the strategic embedding and unique bonding form of nitrogen atoms, their MR effect is significantly enhanced. Finally, 8NN and 8NNP achieve deep-blue emission peaking at 408 and 411 nm, with remarkably narrow full-width at half-maximum (FWHM) of 19 and 17 nm, respectively, and aggregation-enhanced emission characteristics. Additionally, to further tune emission range of this new skeleton, boron-functionalized 8NNB was synthesized, achieving blue emission peaking at 461 nm in toluene, with a FWHM of 31 nm. Finally, the OLEDs based on 8NNP and 8NNB exhibit maximum external quantum efficiencies of 3.47% and 24.24%, with CIE coordinates of (0.172, 0.043) and (0.132, 0.256), respectively. These results validate the rational design of the novel skeleton and facilitate the development of narrowband emission materials.