Engineering Localized Aromaticity in Amine‐Embedded Polycyclic Aromatic Hydrocarbons for Narrowband Fluorescence Emitter

The development of narrowband fluorescent emitters remains a long-standing challenge in organic optoelectronics. Herein, we present an aromaticity engineering approach based on a perylene core to construct highly efficient narrowband fluorescent emitters. Replacement of one naphthalene unit with a carbazole moiety enhances the localization of aromaticity, while extension of the π-conjugation further attenuates the aromaticity of the remaining naphthalene ring. This dual modulation effectively suppresses emission shoulder bands, yielding spectrally pure fluorescence. Consequently, the centrosymmetric c-NaDTCz and the axially symmetric a-NaDTCz exhibit sharp emissions at 536 and 600 nm, with narrow full widths at half-maximum (FWHM) of 17 and 30 nm, respectively. When applied in OLEDs, the c-NaDTCz-based device displays sharp yellow emission peaking at 548 nm with a high external quantum efficiency (EQE) of 26.1%, while a-NaDTCz delivers narrowband red electroluminescence at 610 nm, achieving a record-high EQE of 27.8% for conventional red fluorescent emitters.