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

ABSTRACT 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.