Vibrational wavepacket dynamics in Fe carbene photosensitizer determined with femtosecond X-ray emission and scattering
Kristjan Kunnus, Morgane Vacher, Tobias C. B. Harlang, Kasper S. Kjær, Kristoffer Haldrup, Elisa Biasin, Tim B. van Driel, Mátyás Pápai, Pavel Chabera, Yizhu Liu, Hideyuki Tatsuno, Cornelia Timm, Erik Källman, Mickaël Delcey, Robert W. Hartsock, Marco E. Reinhard, Sergey Koroidov, Mads G. Laursen, Frederik B. Hansen, Peter Vester, Morten Christensen, Lise Sandberg, Zoltán Németh, Dorottya Sárosiné Szemes, Éva Bajnóczi, Roberto Alonso-Mori, James M. Glownia, Silke Nelson, Marcin Sikorski, Dimosthenis Sokaras, Henrik T. Lemke, Sophie E. Canton, Klaus B. Møller, Martin M. Nielsen, György Vankó, Kenneth Wärnmark, Villy Sundström, Petter Persson, Marcus Lundberg, Jens Uhlig, Kelly J. Gaffney
Abstract
Abstract The non-equilibrium dynamics of electrons and nuclei govern the function of photoactive materials. Disentangling these dynamics remains a critical goal for understanding photoactive materials. Here we investigate the photoinduced dynamics of the [Fe(bmip) 2 ] 2+ photosensitizer, where bmip = 2,6-bis(3-methyl-imidazole-1-ylidine)-pyridine, with simultaneous femtosecond-resolution Fe Kα and Kβ X-ray emission spectroscopy (XES) and X-ray solution scattering (XSS). This measurement shows temporal oscillations in the XES and XSS difference signals with the same 278 fs period oscillation. These oscillations originate from an Fe-ligand stretching vibrational wavepacket on a triplet metal-centered ( 3 MC) excited state surface. This 3 MC state is populated with a 110 fs time constant by 40% of the excited molecules while the rest relax to a 3 MLCT excited state. The sensitivity of the Kα XES to molecular structure results from a 0.7% average Fe-ligand bond length shift between the 1 s and 2p core-ionized states surfaces.