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Thermally Activated Delayed Fluorescence and Room-Temperature Phosphorescence in Asymmetric Phenoxazine-Quinoline (D2-A) Conjugates and Dual Electroluminescence
Dey S., Hasan M., Shukla A., Acharya N., Upadhyay M., Lo S.-C., Namdas E.B.,
Published in American Chemical Society
Volume: 126
Issue: 12
Pages: 5649 - 5657
Triplet energy harvesting via either thermally activated delayed fluorescence (TADF) or room-temperature phosphorescence (RTP) from pure organic systems has attracted great attention in the field of organic light-emitting diodes, sensing, and bioimaging. However, the realization of dual electroluminescence via TADF and RTP in single molecules remains elusive. Herein, we report two phenoxazine-quinoline conjugates (DPQ and DPQM) in which two phenoxazine donors are covalently attached to the 6,8-positions of 2,4-diphenylquinoline and/or 7-methyl-2,4-diphenylquinoline acceptors. Experimental and quantum chemistry calculations combining reference compounds (o-PQP, p-PQP, Phox, and QPP) reveal that both conjugates show TADF (with different rate constants of reverse intersystem crossing, krISC= 0.43-1.30 × 106s-1) via reverse intersystem crossing from the charge transfer triplet (3CT) to singlet (1CT) states mediated by vibronic coupling among 1CT, local triplet (3LE), and 3CT states due to close energy gaps. Further, RTP with quantum yields (φP) of ca. 21-24% features was also observed due to the radiative decay of 3LE states. Phosphorescence measurements of DPQM at low temperatures (T = 77, 10 K) ensure a distinct zero-field splitting of T1(CT) into substates. Both compounds showed dual electroluminescence with external quantum efficiencies of ca. 11-12% due to the efficient triplet harvesting from both TADF and RTP channels. © 2022 American Chemical Society. All rights reserved.
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