Joint experimental and theoretical investigation of excited state vibrational coherences in Mn single molecule magnets Julien Eng 1 , K. Barlow 2 , E. Brechin 2 , J.O. Johansson 2 , T.J. Penfold 1 1 Newcastle University, UK, 2 University of Edinburgh, UK Single molecule magnets (SMM) are typically large poly-metallic molecules with two degenerate magnetic ground states that retain magnetisation under a so-called "blocking temperature". In d-metal molecules, the blocking temperature is very low, rendering most industrial applications impossible. The lowest blocking temperature is observed in the Mn 12 complex that retains magnetisation for months below 2K 1 . Magnetic recording using femtosecond laser pulses has recently been achieved in some dielectric media, showing potential for ultrafast data storage applications 2 . Light control of magnetisation represents a great challenge in the field of data storage as it opens the way for larger and more compact storage arrays. Yet, SMMs remain largely unexplored using ultrafast techniques.
In this work 3,4 , we investigate the photophysics and excited-state relaxation of a trinuclear µ3-oxo-bridged Mn(III) SMM, whose magnetic anisotropy is closely related to the Jahn–Teller distortion. Ultrafast transient absorption spectroscopy in solution reveals oscillations superimposed on the decay traces due to a vibrational wavepacket. A joint experimental and theoretical study on Mn monomers allows to shine light on the origin of the vibrational coherences observed experimentally on the larger Mn3 complex. It is shown to emanate from the µ3-oxo-bridge effectively constraining the wavepacket motions along the Jahn-Teller axis. Our results provide new possibilities for optical control of the magnetisation in SMMs and open up new molecular-design challenges to control the wavepacket behaviour in the excited state of SMMs. References 1. D. Gatteschi and R. Sessoli, Angewandte Chemie 115 (2003) 278-309 2. A. Stupakiewicz, K. Szerenos, D. Afanasiev, A. Kirilyuk and A.V. Kimel, Nature 542 (2017) 71-74 3. F. Liedy, J. Eng, R. McNab, R. Inglis, T.J. Penfold, E.K. Brechin and J.O. Johansson, Nature Chemistry 12 (2020) 452-458 4. K. Barlow, J. Eng, I. Ivalo, M. Coletta, E.K. Brechin, T.J. Penfold and J.O. Johansson, Dalton Transactions 15 (2022) 10751- 10757
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