Realizing highly efficient electrofluorescence through a co-axial hybrid local and charge-transfer (HLCT) excited state

In this work, we report two high-performance donor-acceptor (D-A) electrofluorescent materials DPXZ-PI and DPXZ-PICN which are designed with novel co-axial hybrid local and charge-transfer (HLCT) excited states. The co-axial HLCT state features the direct bonding of a strong electron donor diphenoxazine (DPXZ) with a weak electron acceptor phenanthroimidazole (PI). This co-axial HLCT state is initially constructed in DPXZ-PI resulting in a high photoluminescence quantum yield (PLQY) of 81.7% and a high maximum external quantum efficiency (EQE) of 14.8% in a doped organic light-emitting diode (OLED), which is among the best results obtained for HLCT emitter-based OLEDs. Notably, the co-axial HLCT state is stable upon the introduction of the strong electron acceptor cyano-benzene, thus allowing an increase in the electron mobility in the OLED and resulting in a high EQE of 11.6% in a non-doped OLED based on DPXZ-PICN. Overall, the co-axial HLCT state facilitates an increase in the PLQY while maintaining exciton utilizing efficiency (EUE) in the OLED, and thus it is an effective instrument for producing highly-efficient electrofluorescent materials and devices.