Achieving Balanced Electrical Performance of Host Material through Dual N–P═O Resonance Linkage for Efficient Electroluminescence

Developing high-performance host materials is one of the biggest challenges for blue and white thermally activated delayed-fluorescence (TADF) organic light-emitting diode (OLED) technology due to the rigorous requirements of both efficient carrier flux ability and high triplet energy (ET) levels in static donor–acceptor molecules. Here, with the aid of a dual-resonance strategy, a host molecule showing dynamic adaption features in the acceptor–resonance–donor–resonance–acceptor (A–r–D–r–A) molecular configuration has been successfully developed through the implantation of two acceptors of diphenylphosphine oxide into electron-donating 5,10-dihydrophenazine with N–P═O resonance linkages. Owing to the dual enantiotropic N+═P–O– resonances, the designed A–r–D–r–A molecule exhibits an extraordinarily balanced charge flux transportation attribute at high ET (2.96 eV). Excitingly, blue and warm-white TADF OLEDs hosted by the A–r–D–r–A molecule exhibit outstanding external quantum efficiencies of 14.7 and 20.3%, respectively. Our studies not only broaden the scope of resonance molecules but also indicate that a resonance structure is an effective linkage to develop optoelectronic materials with dynamically adaptive properties.