Intramolecular-Locking Modification Enables Efficient Asymmetric Donor-Acceptor-Donor’ Type Ultraviolet Emitters for High-Performance OLEDs with Reduced Efficiency Roll-Off and High Color Purity

Abstract

Developing high-performance ultraviolet organic light-emitting diodes with low efficiency roll-off and high color purity remains challenging due to their inherent wide bandgap characteristics. In this work, we present an intramolecular noncovalent bond locking strategy to modulate donor-acceptor-donor’ (D-A-D’) type ultraviolet fluorophores (mPImCZ2F, mPIoCZ2F and mPImCP2F) with a hot-exciton mechanism. Notably, these asymmetric emitters exhibit significantly enhanced bipolar transport capacity and fluorescence efficiency compared to their counterparts. Among them, mPIoCZ2F exhibits more remarkable the intramolecular locking effect due to multiple C−H···F interactions and ortho-substitution induced steric hindrance, which endows it with a higher radiation rate, narrower emission spectrum, and more balanced charge transport. Consequently, mPIoCZ2F-based non-doped device achieves an electroluminescence (EL) peak at 393 nm with a maximum external quantum efficiency (EQE) of 6.62%. Moreover, in the doped device, mPIoCZ2F emits stable ultraviolet light with an EL peak at 391 nm and a full width at half maximum (FWHM) of 40 nm, corresponding to color coordinates of (0.167, 0.025). It also exhibits an exceptionally high EQE of 8.71% and minimal efficiency roll-off (7.95% at 1000 cd m−2), ranking among the best EL efficiencies reported for UV-OLEDs at high brightness levels.