High-performance narrowband blue electroluminescence with EQE approaching 20% based on hybridized local and charge-transfer multi-resonant molecules

Designing multi-resonant (MR) materials that integrate narrowband emission and efficient exciton utilization remains challenging, especially for indolocarbazole (ICz) cores. To address this, two novel ICz-derived MR emitters, 4CzmICz and 4CzpICz, were developed by strategically extending π-conjugation <i>via</i> peripheral carbazole units. This modulates charge-transfer (CT) states while retaining MR character, endowing both molecules with hybridized local and charge transfer (HLCT) properties. The <i>meta</i>-isomer 4CzmICz exhibits exceptional deep-blue emission (430 nm, FWHM = 14 nm in hexane). The <i>para</i>-isomer 4CzpICz achieves record HLCT-OLED performance: a narrowband device (FWHM = 29 nm) with 19.5% external quantum efficiency (EQE). In an exciplex-sensitized configuration, EQE reaches 25.0% without emission broadening. This work pioneers MR-HLCT integration and establishes a roadmap for next-generation OLED materials.