High‐Efficiency Deep‐Blue Narrowband Electroluminescence via Multi‐Sensitization Using a D‐ meta ‐π‐A Sensitizing Host

The strategic integration of thermally activated delayed fluorescence (TADF) sensitizers has emerged as a critical approach for triplet recycling in organic light‐emitting diodes (OLEDs) with multiple resonance (MR) emitters. However, conventional single‐sensitizer systems are frequently limited by slow exciton utilization and thus severe efficiency roll‐off. This study develops a multi‐sensitization strategy through the integrated design of a novel sensitizing host and parallel energy‐transfer pathways to accelerate exciton utilization. The novel D‐ meta ‐π‐A host exhibits a reverse intersystem crossing rate of 3.18 × 10 6 s −1 and a radiative decay rate of 1.94 × 10 7 s −1 , together with balanced charge transport and blue‐shifted photoluminescence in the neat film. Its photophysical behavior is consistent with contributions from both intra‐ and intermolecular charge‐transfer (CT) states. The optimized device demonstrates remarkable electroluminescence performance with a maximum external quantum efficiency (EQE) of 37.1%, a record‐high EQE of 32.4% at 5,000 cd m −2 , a turn‐on voltage (at 1 cd m −2 ) of 2.4 V, and a maximum power efficiency (PE) of 58.0 lm W −1 , exhibiting deep‐blue emission, ultra‐low power consumption, and suppressed efficiency roll‐off. This work provides a viable design paradigm for high‐performance MR‐OLEDs through synergistic exciton management and sensitizer engineering.