학술논문
Origin of vibrational wavepacket dynamics in Fe carbene photosensitizer determined with femtosecond X-ray emission and scattering
Document Type
Working Paper
Author
Kunnus, Kristjan; Vacher, Morgane; Harlang, Tobias C. B.; Kjær, Kasper S.; Haldrup, Kristoffer; Biasin, Elisa; van Driel, Tim B.; Pápa, Mátyás; Chabera, Pavel; Liu, Yizhu; Tatsuno, Hideyuki; Timm, Cornelia; Källman, Erik; Delcey, Mickaël; Hartsock, Robert W.; Reinhard, Marco E.; Koroidov, Sergey; Laursen, Mads G.; Hansen, Frederik B.; Vester, Peter; Christensen, Morten; Sandberg, Lise; Németh, Zoltán; Szemes, Dorottya Sárosiné; Bajnóczi, Éva; Alonso-Mori, Roberto; Glownia, James M.; Nelson, Silke; Sikorski, Marcin; Sokaras, Dimosthenis; Lemke, Henrik T.; Canton, Sophie; Møller, Klaus B.; Nielsen, Martin M.; Vankó, György; Wärnmark, Kenneth; Sundström, Villy; Persson, Petter; Lundberg, Marcus; Uhlig, Jens; Gaffney, Kelly J.
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Abstract
Disentangling the dynamics of electrons and nuclei during nonadiabatic molecular transformations remains a considerable experimental challenge. Here we have investigated photoinduced electron transfer dynamics following a metal-to-ligand charge-transfer (MLCT) excitation of the [Fe(bmip)2]2+ photosensitizer, where bmip = 2,6-bis(3-methyl-imidazole-1- ylidine)-pyridine, with simultaneous femtosecond-resolution Fe K{\alpha} and K\b{eta} X-ray Emission Spectroscopy (XES) and Wide Angle X-ray Scattering (WAXS). This measurement clearly shows temporal oscillations in the XES and WAXS difference signals with the same 278 fs period oscillation. The oscillatory signal originates from an Fe-ligand stretching mode vibrational wavepacket on a triplet metal-centered (3MC) excited state surface. The vibrational wavepacket is created by 40% of the excited population that undergoes electron transfer from the non-equilibrium MLCT excited state to the 3MC excited state with a 110 fs time constant, while the other 60% relaxes to a 3MLCT excited state in parallel. The sensitivity of the K{\alpha} XES spectrum to molecular structure results from core-level vibronic coupling, due to a 0.7% average Fe-ligand bond length difference in the lowest energy geometry of the 1s and 2p core-ionized states. These results highlight the importance of vibronic effects in time-resolved XES experiments and demonstrate the role of metal-centered excited states in the electronic excited state relaxation dynamics of an Fe carbene photosensitizer.