Guest-host interactions investigated by time-resolved X-ray spectroscopies and scattering at MHz rates: Solvation dynamics and photoinduced spin transition in aqueous Fe(bipy)32+

K. Haldrup, G. Vankó, W. Gawelda, A. Galler, G. Doumy, A. M. March, E. P. Kanter, A. Bordage, A. Dohn, T. B. Van Driel, K. S. Kjær, H. T. Lemke, S. E. Canton, J. Uhlig, V. Sundström, L. Young, S. H. Southworth, M. M. Nielsen, C. Bressler

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Abstract

We have studied the photoinduced low spin (LS) to high spin (HS) conversion of [Fe(bipy)3]2+ in aqueous solution. In a laser pump/X-ray probe synchrotron setup permitting simultaneous, time-resolved X-ray diffuse scattering (XDS) and X-ray spectroscopic measurements at a 3.26 MHz repetition rate, we observed the interplay between intramolecular dynamics and the intermolecular caging solvent response with better than 100 ps time resolution. On this time scale, the initial ultrafast spin transition and the associated intramolecular geometric structure changes are long completed, as is the solvent heating due to the initial energy dissipation from the excited HS molecule. Combining information from X-ray emission spectroscopy and scattering, the excitation fraction as well as the temperature and density changes of the solvent can be closely followed on the subnanosecond time scale of the HS lifetime, allowing the detection of an ultrafast change in bulk solvent density. An analysis approach directly utilizing the spectroscopic data in the XDS analysis effectively reduces the number of free parameters, and both combined permit extraction of information about the ultrafast structural dynamics of the caging solvent, in particular, a decrease in the number of water molecules in the first solvation shell is inferred, as predicted by recent theoretical work.

Original languageEnglish
Pages (from-to)9878-9887
Number of pages10
JournalJournal of Physical Chemistry A
Volume116
Issue number40
DOIs
Publication statusPublished - Oct 11 2012

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

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    Haldrup, K., Vankó, G., Gawelda, W., Galler, A., Doumy, G., March, A. M., Kanter, E. P., Bordage, A., Dohn, A., Van Driel, T. B., Kjær, K. S., Lemke, H. T., Canton, S. E., Uhlig, J., Sundström, V., Young, L., Southworth, S. H., Nielsen, M. M., & Bressler, C. (2012). Guest-host interactions investigated by time-resolved X-ray spectroscopies and scattering at MHz rates: Solvation dynamics and photoinduced spin transition in aqueous Fe(bipy)32+. Journal of Physical Chemistry A, 116(40), 9878-9887. https://doi.org/10.1021/jp306917x