AIE‐Active Multiresonance TADF Emitters via Quadrupolar Donor–Acceptor–Donor Modification for Blue OLEDs

We report blue aggregation‐induced emission (AIE)‐active multiresonance thermally activated delayed fluorescence (MR‐TADF) emitters that pair a rigid MR core with highly twisted donors, phenoxazine (PXZ) and phenothiazine (PTZ), to yield 2PXZ‐CyDOBNA and 2PTZ‐CyDOBNA , respectively. The quadrupolar donor–acceptor‐donor (D–A–D) modification effectively tunes key optoelectronic parameters, notably increasing the experimentally estimated reverse intersystem‐crossing rate constants to approximately 5 × 10 5 s −1 . However, subtle donor substitutions lead to contrasting luminescence behaviors in the solution and aggregated states. In strongly polar solvents, 2PXZ‐CyDOBNA exhibits pronounced dual emission, arising from both MR‐core fluorescence and PXZ‐mediated D‐to‐A charge–transfer. More strikingly, 2PXZ‐CyDOBNA showed ~40‐fold AIE enhancement while retaining robust TADF, whereas 2PTZ‐CyDOBNA displayed much weaker AIE. Photophysical measurements together with single‐crystal X‐ray analysis reveal that 2PXZ‐CyDOBNA adopts a highly twisted quadrupolar D–A–D geometry and forms dimers without direct face‐to‐face π – π stacking; instead, a network of intra/intermolecular interactions (e.g., hydrogen bonding, CH··· π and π ··· π interactions) stabilizes the dimer and its packing—features that distinguish it from 2PTZ‐CyDOBNA . Furthermore, 2PXZ‐CyDOBNA demonstrated promising OLED performance, with an EQE max of 7.24% and a CIEy of 0.183 in TADF‐sensitized fluorescence OLEDs, indicating deep‐blue emission. Overall, these results clarify the design principles of AIE‐MR‐TADF systems and highlight their potential for use in advanced optoelectronics.