Symmetric Deep‐Blue Hot Exciton Emitter Dominated by Locally Excited State Anti‐Kasha Emission

Abstract The advancement of deep‐blue luminophores with high efficiency, color purity, and stable characteristics remains hindered by the absence of effective molecular design methodologies. Herein, a proof‐of‐concept deep blue hot exciton emitter, namely 2ANAC is designed and synthesized, featuring a rod‐like, symmetric π‐donor‐σ‐donor‐π (π‐D‐σ‐D‐π) molecular architecture to address the above challenges. The symmetric molecular structure endows numerous degenerate excited state characteristics, facilitating intersystem crossing between energy closely singlet and triplet states. Owing to nearly perpendicular conformation between the D‐π moieties, the formed low‐lying singlet excited (S 1 to S 4 ) states exhibit minimal oscillator strengths. In contrast, the fifth singlet excited (S 5 ) state boasts a significantly higher oscillator strength. This indicates the potential for anti‐Kasha emission behavior, thus promoting the highly emissive deep‐blue luminescence from the locally excited state with a relatively small full width at half maximum. Furthermore, the long‐axial molecular architecture confers as high as 90% of the horizontal dipole ratio. The corresponding non‐doped deep‐blue OLED based on 2ANAC exhibits an outstanding maximum external quantum efficiency of 10.8% with minimal efficiency roll‐off, representing one of the highest reported values for deep‐blue hot exciton OLEDs.