TADF dendronized polymer with vibrationally enhanced direct spin-flip between charge-transfer states for efficient non-doped solution-processed OLEDs

Li, Chensen; Harrison, Alastair K.; Liu, Yuchao; Zhao, Zhennan; Dias, Fernando B.; Zeng, Cheng; Yan, Shouke; Bryce, Martin R.; Ren, Zhongjie

Abstract

A novel type of thermally activated delayed fluorescence (TADF) dendronized polymer was designed and synthesized. Firstly, one side of the asymmetric TADF unit was encapsulated by 3,6-di-tert-butylcarbazole via a conjugated linkage with strong twisted intramolecular charge transfer (TICT) to minimize the energy gap between 1CT and 3CT, and then the peripheral dicarbazole connects in a non-conjugated way on the other side, showing weak TICT and high-lying 3LE&3CT state; finally, a linear dendronized polymer, PDCDC, was obtained by introducing the alkyl polymer backbone as main chains. As far as we know, this is the first blue or greenish-blue-emitting TADF dendronized polymer. For PDCDC, the spin-forbidden 1CT ↔ 3CT transitions are activated by molecular vibrations, which combine with a small energy gap and reorganization energy to enable 1CT ↔ 3CT spin-flip transition rates reaching 106 s−1 with negligible role of a second triplet state. Films of PDCDC show a double exponential decay (prompt fluorescence and delayed fluorescence) in the presence of oxygen due to a low oxygen permeability ascribed to the entangled polymeric backbone which increases film density. Besides, obvious aggregation-enhanced emission (AEE) property can minimize the exciton quenching in aggregated states. A maximum external quantum efficiency of 9.0% for non-doped PDCDC-based organic light-emitting diodes (OLEDs) can be obtained. To the best of our knowledge, these are the most efficient dendronized polymer devices with blue or greenish-blue emission.

Citation

Li, C., Harrison, A. K., Liu, Y., Zhao, Z., Dias, F. B., Zeng, C., …Ren, Z. (2022). TADF dendronized polymer with vibrationally enhanced direct spin-flip between charge-transfer states for efficient non-doped solution-processed OLEDs. Chemical Engineering Journal, 435, Article 134924. https://doi.org/10.1016/j.cej.2022.134924

• Journal Article Type: Article
• Acceptance Date: Jan 22, 2022
• Online Publication Date: Feb 11, 2022
• Publication Date: 2022-05
• Deposit Date: May 26, 2022
• Publicly Available Date: May 26, 2022
• Journal: Chemical Engineering Journal
• Print ISSN: 1385-8947
• Publisher: Elsevier
• Peer Reviewed: Peer Reviewed
• Volume: 435
• Article Number: 134924
• DOI: https://doi.org/10.1016/j.cej.2022.134924
• Public URL: https://durham-repository.worktribe.com/output/1205683