B-O Covalent Bonds Annulated Hot Exciton Molecular Design for High-Performance Narrowband UV-OLEDs

Abstract

Narrowband ultraviolet (UV) emission is highly desirable for numerous advanced applications, including bioimaging, sterilization, and optoelectronic devices, yet the development of high-performance narrowband UV emitters remains a critical challenge due to the difficulty in balancing a large optical bandgap, high emission efficiency, and narrow full-width at half-maximum (FWHM). Herein, we designed and synthesized a UV-emissive hot exciton emitter DOBCzDBO by combining the electron-accepting DOBNA fragment (endowing high photoluminescence quantum yield (PLQY) and thermal stability) with rigid carbazole unit, and precisely regulated its near-ultraviolet emission and color purity via B-O covalent bonds annulation on the carbazole. Theoretical calculations and photophysical investigations confirm that DOBCzDBO possesses typical hybridized local and charge-transfer (HLCT) characteristics/hot exciton behaviors. Notably, DOBCzDBO exhibits significant electroluminescence (EL) performance, achieving intense UV emission at 391 nm with a full-width at half-maximum (FWHM) of 24 nm, a maximum external quantum efficiency (EQEₘₐₓ) of 8.9%, and a CIEᵧ value of 0.020. To the best of our knowledge, its FWHM is among the narrowest reported for HLCT-based UV-OLEDs, providing a promising molecular design strategy to break the bottleneck of high-performance narrowband UV emitters.