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.