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

초록

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 x 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 similar to 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 pi-pi stacking; instead, a network of intra/intermolecular interactions (e.g., hydrogen bonding, C-H center dot center dot center dot pi and pi center dot center dot center dot pi 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.

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