Pyrazine-fused polycyclic aromatic hydrocarbons towards efficient multiple-resonance narrowband deep-blue emission

Developing organic multiple-resonance (MR) deep-blue emitters with narrow full widths at half maximum (FWHMs) is crucial for enhancing the color purity of organic light-emitting diodes (OLEDs). However, the exploration of new MR cores remains very limited to date. Furthermore, redshifting the emission color of MR emitters is also a formidable challenge. Pyrazine, characterized by its planar and rigid structure, exhibits a strong electronegativity, which may make it a promising candidate for constructing MR emitters with a red shifted emission compared to indolo[3,2,1-jk]carbazole (ICz)-based MR molecules. Herein, a series of polycyclic aromatic hydrocarbons (PAHs) with MR characteristics are designed and synthesized by integrating a pyrazine core with various electron-donating segments, which exhibit the narrowband deep-blue emission peaks ranging from 423 to 459 nm with FWHMs < 50 nm in toluene. It is demonstrated that increasing donor strength and changing meta- to para-oriented nitrogen atom can induce the bathochromic emission. Theoretical investigations reveal that the non-bonding orbital characteristic of pyrazine suppress the undesired stretching vibration and promote resonance effect. The optimized deep-blue OLEDs fabricated with the pyrazine-embedded MR emitters demonstrate a high external quantum efficiency (EQE) of 23.5%, and narrowband emission with an electroluminescence peak at 454 nm.