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Lookup NU author(s): Dr Julien EngORCiD, Professor Thomas PenfoldORCiD
This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).
The photoinduced Jahn-Teller (JT) switch in Mn(acac)₃ provides a model for how ultrafast structural dynamics can be harnessed to control magnetic anisotropy in singlemolecule magnets (SMMs). However, the role of excitation energy in governing the efficiency and pathway of this transformation remains unclear. Here, ultrafast transient absorption spectroscopy (380-940 nm) probes the excitation-energy dependence of the JT switch. Selective excitation of Q₁, Q₂, and Q₃,₄ states shows that all pathways converge to a long-lived compressed-state photoproduct, but with distinct relaxation timescales, vibrational dynamics, and yields. Vibrational coherence analysis reveals modes at 170, 208, and 254 cm⁻¹, assigned to the elongated, Q₁ excited, and compressed state configurations, respectively. The 208 cm⁻¹ mode is observed only under direct Q₁ excitation, indicating excitation-dependent access to the JT-reactive coordinate. The compressed-state yield exhibits a strong dependence on excitation energy. For excitation into the lowest Q₁ state (940-700 nm), the yield increases and follows a one-dimensional Landau-Zener model, where higher wavepacket velocity along the JT coordinate enhances nonadiabatic transition probability. The yield plateaus between 700-640 nm as the Q₂ state is accessed and excess energy is likely transferred into non-reactive modes. Upon excitation into the Q₃,₄ manifold, the yield increases sharply, reaching a maximum near 470 nm before decreasing at higher energies, revealing the onset of multidimensional dynamics and competing relaxation pathways. These results identify excitation energy as a control parameter for the nonadiabatic structural dynamics, providing design rules for optically steering magnetic anisotropy in SMMs.
Author(s): Paine B, Eng J, Barlow K, Penfold TJ, Johansson JO, Green AE, Phelps R
Publication type: Article
Publication status: Published
Journal: Physical Chemistry Chemical Physics
Year: 2026
Pages: epub ahead of print
Online publication date: 26/08/2026
Acceptance date: 25/08/2026
Date deposited: 01/09/2026
ISSN (print): 1463-9076
ISSN (electronic): 1463-9084
Publisher: Royal Society of Chemistry
URL: https://doi.org/10.1039/D6CP02713J
DOI: 10.1039/D6CP02713J
Data Access Statement: The dataset supporting this paper are openly available from eData the STFC Research Data repository
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