Ultrafast spin and charge dynamics in molecular magnets
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Ultrafast spin and charge dynamics in molecular magnets
Wed, 19/02/2020 - 13:30 to 14:30
Location:
Speaker:
Dr Olof Johansson
Affiliation:
University of Edinburgh
Synopsis:
During the last 20 years, ultrafast transient absorption measurements of transition metal complexes have altered the understanding of how fast the spin-state of a molecule can change in the excited state. Notably, Fe(II) complexes can be switched from low-spin S = 0 to high-spin S = 2 in in less than 200 fs after absorbing only one photon [1–3], and similar processes have been observed in Cr(acac)3 [4,5]. We have studied a range of large transition metal complexes with exchange-coupled electrons, ranging from single-molecule magnets to magnetic coordination polymers, to explore ultrafast spin dynamics in molecules with several magnetic centres. We report the first ultrafast magneto-optical (MO) study of a molecule-based magnet [6]. Thin films of the V-Cr Prussian blue analogue were studied and the MO measurements could detect a change in the super-exchange interaction taking place as a result of a spin flip occurring via intersystem crossing in less than 250 fs after the absorption of a pump photon. We have also carried out measurements on a tri-nuclear Mn(III)-based single-molecule magnet, whose magnetic anisotropy is closely related to the Jahn-Teller (JT) distortion. Ultrafast transient absorption spectroscopy in solution reveals oscillations superimposed on the decay traces with corresponding energies around 200 cm−1, coinciding with a vibrational mode along the JT axis. The oscillations arise due to a wave packet forming as the molecule adjust to the new JT geometry in the excited state [7].
[1] J. E. Monat and J. K. McCusker, J. Am. Chem. Soc. 122, 4092 (2000).
[2] G. Auböck and M. Chergui, Nat. Chem. 7, 629 (2015).
[3] H. T. Lemke, K. S. Kjær, R. Hartsock, T. B. van Driel, M. Chollet, J. M. Glownia, S. Song, D. Zhu, E. Pace, S. F. Matar, M. M. Nielsen, M. Benfatto, K. J. Gaffney, E. Collet, and M. Cammarata, Nat. Commun. 8, 15342 (2017).
[4] E. A. Juban and J. K. McCusker, J. Am. Chem. Soc. 127, 6857 (2005).
[5] J. N. Schrauben, K. L. Dillman, W. F. Beck, and J. K. McCusker, Chem. Sci. 1, 405 (2010).
[6] J. O. Johansson, J.-W. Kim, E. Allwright, D. M. Rogers, N. Robertson, and J.-Y. Bigot, Chem. Sci. 7, 7061 (2016).
[7] F. Liedy, J. Eng, R. McNab, R. Inglis, T. Penfold, E. K. Brechin, and J. O. Johansson, ChemRxiv (2019).