Conformational Isomerization Promotes Balanced Ambipolar Transport for Efficient Narrowband Near-Ultraviolet Fluorophore and Non-doped Device with Low Efficiency Roll-Off

Abstract

Near-ultraviolet (NUV) organic light-emitting diodes have garnered significant attention, yet the unbalanced ambipolar transport in emitters often leads to poor electroluminescence efficiency and serious roll-off in the non-doped device. Here, a novel NUV fluorophore, namely, 3,6-CNCzC3, exhibiting a hybridized local and charge transfer state, was developed by regulating the substitution pattern. The conformational isomerization endows it with balanced electron/hole mobilities in both low and high electric fields, while the suppression of structural relaxation and low-frequency vibronic coupling in the excited state promotes spectral narrowing. Consequently, the non-doped 3,6-CNCzC3-based device not only shows a narrow full width at half-maximum of 44 nm and color coordinates of (0.161, 0.028), but also exhibits a maximum external quantum efficiency of 6.69% and maintains a noteworthy value of 5.95% at 1000 cd m −2 , which is one of the best values among non-doped NUV-OLEDs at a high luminance level.