Enhancing Thermally Activated Delayed Fluorescence by Fine-Tuning the Dendron Donor Strength

Eimantas Duda, David Hall, Sergey Bagnich, Cameron L. Carpenter-Warren, Rishabh Saxena, Michael Y. Wong, David B. Cordes, Alexandra M.Z. Slawin, David Beljonne, Yoann Olivier, Eli Zysman-Colman, Anna Köhler

Research output: Contribution to journalArticlepeer-review

Abstract

Thermally activated delayed fluorescence (TADF) relies on a small energy gap between the emissive singlet and the nonemissive triplet state, obtained by reducing the wave function overlap between donor and acceptor moieties. Efficient emission, however, requires maintaining a good oscillator strength, which is itself based on sufficient overlap of the wave functions between donor and acceptor moieties. We demonstrate an approach to subtly fine-tune the required wave function overlap by employing donor dendrons of changing functionality. We use a carbazolyl-phthalonitrile based donor–acceptor core (2CzPN) as a reference emitter and progressively localize the hole density through substitution at the 3,6-positions of the carbazole donors (Cz) with further carbazole, (4-tert-butylphenyl)amine (tBuDPA), and phenoxazine (PXZ). Using detailed photoluminescence studies, complemented with density functional theory (DFT) calculations, we show that this approach permits a gradual decrease of the singlet–triplet gap, ΔEST, from 300 to around 10 meV in toluene, yet we also demonstrate why a small ΔEST alone is not enough. While sufficient oscillator strength is maintained with the Cz- and tBuDPA-based donor dendrons, this is not the case for the PXZ-based donor dendron, where the wave function overlap is reduced too strongly. Overall, we find the donor dendron extension approach allows successful fine-tuning of the emitter photoluminescence properties.

Original languageEnglish
Pages (from-to)552-562
Number of pages11
JournalJournal of physical chemistry B
Volume126
Issue number2
DOIs
Publication statusPublished - 20 Jan 2022

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