Exploring the Early Time Behavior of the Excited States of an Archetype Thermally Activated Delayed Fluorescence Molecule

Franca, Larissa G.; Danos, Andrew; Saxena, Rishabh; Kuila, Suman; Stavrou, Kleitos; Li, Chunyong; Wedler, Stefan; Köhler, Anna; Monkman, Andrew P.

Abstract

Optical pump–probe techniques allow for an in-depth study of dark excited states. Here, we utilize them to map and gain insights into the excited states involved in the thermally activated delayed fluorescence (TADF) mechanism of a benchmark TADF emitter DMAC-TRZ. The results identify different electronic excited states involved in the key TADF transitions and their nature by combining pump–probe and photoluminescence measurements. The photoinduced absorption signals are highly dependent on polarity, affecting the transition oscillator strength but not their relative energy positions. In methylcyclohexane, a strong and vibronically structured local triplet excited state absorption (3LE → 3LE n ) is observed, which is quenched in higher polarity solvents as 3CT becomes the lowest triplet state. Furthermore, ultrafast transient absorption (fsTA) confirms the presence of two stable conformers of DMAC-TRZ: (1) quasi-axial (QA) interconverting within 20 ps into (2) quasi-equatorial (QE) in the excited state. Moreover, fsTA highlights how sensitive excited state couplings are to the environment and the molecular conformation.

Citation

Franca, L., Danos, A., Saxena, R., Kuila, S., Stavrou, K., Li, C., …Monkman, A. P. (2024). Exploring the Early Time Behavior of the Excited States of an Archetype Thermally Activated Delayed Fluorescence Molecule. Journal of Physical Chemistry Letters, 15(6), 1734-1740. https://doi.org/10.1021/acs.jpclett.4c00030

• Journal Article Type: Article
• Acceptance Date: Feb 2, 2024
• Online Publication Date: Feb 7, 2024
• Publication Date: Feb 15, 2024
• Deposit Date: Mar 14, 2024
• Publicly Available Date: Mar 14, 2024
• Journal: The Journal of Physical Chemistry Letters
• Publisher: American Chemical Society
• Peer Reviewed: Peer Reviewed
• Volume: 15
• Issue: 6
• Pages: 1734-1740
• DOI: https://doi.org/10.1021/acs.jpclett.4c00030
• Public URL: https://durham-repository.worktribe.com/output/2257953