Thermodynamic equilibrium between locally excited and charge-transfer states through thermally activated charge transfer in 1-(pyren-2′-yl)-o-carborane

Lei Ji*, Stefan Riese, Alexander Schmiedel, Marco Holzapfel, Maximillian Fest, Jörn Nitsch, Basile F.E. Curchod*, Alexandra Friedrich, Lin Wu, Hamad H. Al Mamari, Sebastian Hammer, Jens Pflaum, Mark A. Fox, David J. Tozer, Maik Finze, Christoph Lambert, Todd B. Marder

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

14 Citations (Scopus)
28 Downloads (Pure)

Abstract

Reversible conversion between excited-states plays an important role in many photophysical phenomena. Using 1-(pyren-2′-yl)-o-carborane as a model, we studied the photoinduced reversible charge-transfer (CT) process and the thermodynamic equilibrium between the locally-excited (LE) state and CT state, by combining steady state, time-resolved, and temperature-dependent fluorescence spectroscopy, fs- and ns-transient absorption, and DFT and LR-TDDFT calculations. Our results show that the energy gaps and energy barriers between the LE, CT, and a non-emissive ‘mixed’ state of 1-(pyren-2′-yl)-o-carborane are very small, and all three excited states are accessible at room temperature. The internal-conversion and reverse internal-conversion between LE and CT states are significantly faster than the radiative decay, and the two states have the same lifetimes and are in thermodynamic equilibrium.

Original languageEnglish
Pages (from-to)5205–5219
Number of pages15
JournalChemical Science
Volume13
Issue number18
Early online date19 Apr 2022
DOIs
Publication statusE-pub ahead of print - 19 Apr 2022

Bibliographical note

Funding Information:
TBM thanks the Julius-Maximilians-Universität Würzburg for support. TBM, CL, and JP thank the Bavarian State Ministry of Science, Research, and the Arts (Collaborative Research Network “Solar Technologies Go Hybrid”) and Deutsche Forschungsgemeinschaft (Grant Number: GRK 2112) for funding. LJ thanks the generous financial support from the Natural Science Foundation of China (Grant No. 62174137 to LJ), Natural Science Foundation of Shaanxi Province (Grant No. 2020GXLH-Z-022 to LJ), and Fundamental Research Funds for the Central Universities. JN thanks the DFG for a Return Fellowship (NI1737/2-1). The authors gratefully acknowledge the computational and data resources provided by the Leibniz Supercomputing Centre ( http://www.lrz.de ). This work was carried out with the support of the Diamond Light Source, UK. The raw data are archived in the Diamond Light Source archive under experiment number MT18456. The authors acknowledge support by Sarah Barnett as the local contact at the Diamond Light Source. We thank Prof. Klaus Müller-Buschbaum for helpful discussions.

Publisher Copyright:
© 2022 The Royal Society of Chemistry.

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