B–O covalent bond-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 a narrow full-width at half-maximum (FWHM). Herein, we designed and synthesized a UV-emissive hot exciton emitter (DOBCzDBO) by combining an electron-accepting DOBNA fragment (endowing high photoluminescence quantum yield (PLQY) and thermal stability) with a rigid carbazole unit and precisely regulated its near-ultraviolet emission and color purity via B–O covalent bond 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: specifically, the device with 1 wt% doping exhibits a full-width at half-maximum (FWHM) of 24 nm along with a CIE_y value of 0.020, while the device with 2 wt% doping achieves a maximum external quantum efficiency (EQE_max) of 8.9%. To the best of our knowledge, its FWHM is among the narrowest values reported for HLCT-based UV-OLEDs, providing a promising molecular design strategy to break the bottleneck of high-performance narrowband UV emitters.