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.

doi:10.1021/acs.jpclett.4c00030

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.

Authors

Larissa G. Franca

Dr Andrew Danos andrew.danos@durham.ac.uk
Senior Experimental Officer

Rishabh Saxena

Suman Kuila suman.kuila@durham.ac.uk
Post Doctoral Research Associate

Kleitos Stavrou kleitos.stavrou@durham.ac.uk
Academic Visitor

Dr Chunyong Li chunyong.li@durham.ac.uk
Laser Science Experimental Officer

Stefan Wedler

Anna Köhler

Professor Andrew Monkman a.p.monkman@durham.ac.uk
Professor

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