Aromaticity Localization Effects in Polycyclic Aromatic Hydrocarbons for Discovering Narrowband Fluorescence Materials
Yimin Wu, Junjie Liu, Ge Yang, Zhengyang Bin, Jingsong You
Abstract
Achieving narrowband fluorescence in polycyclic aromatic hydrocarbons (PAHs) is crucial for ultrahigh-definition organic light-emitting diodes (UD-OLEDs), yet the underlying structure–property relationships that dictate emission bandwidth remain insufficiently understood. In this study, we introduce aromaticity localization as a predictive framework for identifying narrowband emitters. Using nucleus-independent chemical shift (NICS) analysis, we uncover a strong correlation between localized aromaticity and reduced vibrational coupling, demonstrating that restricting π-electron delocalization effectively suppresses shoulder peaks, thereby minimizing spectral broadening. To validate this concept, we designed a new class of imine-amine-type PAHs (IA-PAHs) that integrates electron-deficient imine and electron-rich amine units, generating a multiple-resonance-type electronic structure. Building on a steric-hindrance-guided C–H activation strategy, we precisely controlled the regioselectivity of pyridine fusion within the triphenylamine framework, leading to the discovery of narrowband red-emitting II-b and green-emitting III-c featuring localized aromaticity. Notably, II-b exhibited an exceptionally narrowband red emission at 660 nm with a full width at half-maximum of only 35 nm (0.10 eV). OLEDs incorporating II-b demonstrated high efficiency with minimal roll-off and fully met the stringent BT.2020 red standard, with Commission Internationale de l’Eclairage (CIE) coordinates of [0.71, 0.29]. This work not only establishes aromaticity localization as an empirical and intuitive design principle for narrowband fluorophores but also represents a significant advancement in deep-red narrowband OLED technology, setting a new benchmark for conventional fluorescent emitters.