Molecular Ring‐locking Strategy for Narrowband Ultraviolet Organic Electroluminescence with Negligible Efficiency Roll‐Off

Comprehensive Summary

Donor‐acceptor (D‐A) type pure organic fluorophores are pivotal for cost‐effective wide‐color‐gamut displays, yet they often suffer from spectral broadening and efficiency roll‐off, especially in short‐wavelength ultraviolet organic light‐emitting diodes (UV‐OLEDs). Here, we present a ring‐locking strategy for the diphenylbenzimidazole acceptor via intramolecular covalent bonds to rigidify D‐A emitters (mBGCz and mBGtbuCz) with a hybridized local and charge‐transfer state. The resulting emitters exhibit narrowed ultraviolet emission with high photoluminescence quantum yields of 97%, together with extremely low non‐radiative decay rates (<10 ⁷ s ⁻¹ ). The mBGCz‐ and mBGtbuCz‐based devices achieve maximum external quantum efficiencies (EQEs) of 7.88% and 6.71% as well as stable narrowband ultraviolet emission with peak wavelengths at 385 and 389 nm, and color coordinates of (0.166, 0.024) and (0.166, 0.022), respectively. Remarkably, the mBGCz‐based device maintains high EQEs of 7.88% and 7.67% at 500 and 1000 cd·m ⁻² , respectively, and still delivers 7.28% at 1500 cd·m ⁻² , corresponding to negligible efficiency roll‐off. This work provides a viable design strategy to simultaneously overcome the trade‐offs between low luminance, efficiency roll‐off, and color purity in ultraviolet emitters, paving the way for UV‐OLED applications in high‐brightness scenarios.