Multifunctional Deep-Blue Electroluminescent Material Featuring Rigid Twisted Structure for Full-Color OLEDs

High-performance full-color displays and white lighting require stable and efficient red, green, and blue emitters; however, they are often limited by wide bandgaps, imbalanced carrier injection/transport, complex device structures, and high material costs. To address these challenges, we designed and synthesized a multifunctional deep-blue molecule (PPI-F-PO) integrating a phenanthroimidazole moiety, a 9,9-diphenylfluorene unit, and a phosphine oxide group. The twisted structure of fluorene, featuring a sp3-hybridized carbon, effectively suppresses conjugation extension and aggregation-caused quenching, whereas the electron-withdrawing phosphine oxide group enhances electron transport. Consequently, it exhibits good thermal stability, high solid-state photoluminescence quantum yield (58.8%), and high triplet energy (ET = 2.54 eV). Non-doped blue OLEDs based on this emitter achieve a maximum external quantum efficiency (EQE) of 2.52% with deep-blue CIE coordinates of (0.16, 0.06). Moreover, using this material as a host, green and orange-red phosphorescent OLEDs exhibit maximum EQEs of 15.4% and 9.7%, respectively, along with low efficiency roll-off. This work demonstrates that a bipolar deep-blue emitter with high triplet energy can act both as a high-efficiency standalone emitter and as a universal host for lower-energy phosphors, thereby simplifying device architecture and reducing material costs for full-color OLEDs.