Novel phenanthrooxazole acceptor affording an efficient ultraviolet emitter and OLED with minimal roll-off via constitutional isomerization

Abstract

Developing efficient ultraviolet organic electroluminescence materials and devices with an emission wavelength below 400 nm while minimizing efficiency roll-off remains a formidable challenge. Herein, three isomers (p-POBCz, m-POBCz and 3-POBCz) with a hybridized local and charge-transfer (HLCT) excited state characteristic have been developed by strategically incorporating electron-donating unit, phenylcarbazole, into novel rigid phenanthrooxazole acceptor at different attachment sites. Their photophysical and electronic properties can be precisely regulated through molecular isomer manipulation. A maximum external quantum efficiency (EQE) of 6.02 % is achieved in the 3-POBCz-based device, corresponding to color coordinates of (0.159, 0.048), which closely approximates the blue standard for 4K/8K ultrahigh-definition displays. Notably, the device that employs meta-substituted m-POBCz as an emitter, emits stable ultraviolet light with a peak wavelength of 392 nm due to its confined molecular conjugation length. It not only attains an impressive EQE of 6.35 % but also maintains a robust EQE of 6.16 % even at a high luminance of 1000 cd m⁻², demonstrating minimal efficiency roll-off. These findings underscore the promising potential of phenanthrooxazole as an acceptor moiety in the design and synthesis of HLCT materials, thereby opening avenues for the advancement of high-performance wide bandgap emitters and their associated devices.