Molecular Conformation‐Locking for Eye Care and Highly Efficient Narrowband Deep‐Blue Organic Electroluminescence

The advancement of high-color-purity displays demands deep-blue emitters that fulfil stringent colorimetric standards while minimizing photobiological risks to eye health. We propose a skeletal rigidity strategy by fusing a five-membered oxa-heterocycle into a classical MR-TADF skeleton (ν-DABNA), which simultaneously introduces rigidity enhancement via aromatic fusion and conformational locking. This approach resulted in an increased optical bandgap and the formation of intramolecular C-H···O secondary interactions, and thus a systematic blue-shift and narrowing emission spectrum. In toluene solution, the proof-of-concept molecule, v-DABNA-O, exhibits a narrowband deep-blue emission peaking at 460.4 nm, with an ultra-narrow full-width at half maximum (FWHM) of 12.0/69.8 nm/meV. As a result, the ν-DABNA-based device with a sensitizer achieves a maximum external quantum efficiency of 36.1%, a narrow electroluminescence spectrum with an FWHM of 17.9/95.4 nm/meV, and a Commission Internationale de l'Éclairage coordinate of (0.135, 0.091). Crucially, the device achieves a sharp suppression of high-energy emission below 450 nm, directly addressing the imperative for visual safety. This work successfully addresses the trilemma in deep-blue emitters by simultaneously achieving an ultra-narrow emission bandwidth, a precisely positioned emission peak, and suppressed spectral intensity below 450 nm.