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Vibrational Damping Reveals Vibronic Coupling in Thermally Activated Delayed Fluorescence Materials

Hempe, Matthias; Kukhta, Nadzeya A.; Danos, Andrew; Fox, Mark A.; Batsanov, Andrei S.; Monkman, Andrew P.; Bryce, Martin R.

Vibrational Damping Reveals Vibronic Coupling in Thermally Activated Delayed Fluorescence Materials Thumbnail


Authors

Matthias Hempe

Nadzeya A. Kukhta



Abstract

We investigate a series of D–A molecules consisting of spiro[acridan-9,9′-fluorene] as the donor and 2-phenylenepyrimidine as the acceptor. In two of the materials, a spiro center effectively electronically isolates the D unit from (consequently) optically innocent yet structurally influential adamantyl side groups. In a third material, adamantyl groups attached directly to the acceptor strongly influence the electronic properties. Steady-state and time-resolved photophysical studies in solution, Zeonex polymer matrix, and neat films reveal that the substituents impact the efficiency of vibronic coupling between singlet and triplet states relevant to reverse intersystem crossing (rISC) and thermally activated delayed fluorescence (TADF), without significantly changing the singlet–triplet gap in the materials. The adamantyl groups serve to raise the segmental mass and inertia, thereby damping intramolecular motions (both vibrational and rotational). This substitution pattern reveals the role of large-amplitude (primarily D–A dihedral angle rocking) motions on reverse intersystem crossing (rISC), as well as smaller contributions from low-amplitude or dampened vibrations in solid state. We demonstrate that rISC still occurs when the high-amplitude motions are suppressed in Zeonex and discuss various vibronic coupling scenarios that point to an underappreciated role of intersegmental motions that persist in rigid solids. Our results underline the complexity of vibronic couplings in the mediation of rISC and provide a synthetic tool to enable future investigations of vibronic coupling through selective mechanical dampening with no impact on electronic systems.

Citation

Hempe, M., Kukhta, N. A., Danos, A., Fox, M. A., Batsanov, A. S., Monkman, A. P., & Bryce, M. R. (2021). Vibrational Damping Reveals Vibronic Coupling in Thermally Activated Delayed Fluorescence Materials. Chemistry of Materials, 33(9), 3066-3080. https://doi.org/10.1021/acs.chemmater.0c03783

Journal Article Type Article
Online Publication Date Apr 28, 2021
Publication Date 2021-05
Deposit Date May 13, 2021
Publicly Available Date May 14, 2021
Journal Chemistry of Materials
Print ISSN 0897-4756
Electronic ISSN 1520-5002
Publisher American Chemical Society
Peer Reviewed Peer Reviewed
Volume 33
Issue 9
Pages 3066-3080
DOI https://doi.org/10.1021/acs.chemmater.0c03783

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