Master Thesis defense by Lise Ørduk Sandberg – Niels Bohr Institute - University of Copenhagen

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Master Thesis defense by Lise Ørduk Sandberg

Ultrafast Dynamics in
Photoexcited Iron-Carbene Molecules – an X-ray Study

This M.Sc. thesis describes the analysis of time resolved X-ray di↵use scattering data with sub-picosecond time resolution. Through the analysis, I have managed to describe the femtosecond structural dynamics of the iron molecule CAB21, which is a promising photosensitizer candidate due to the very long lifetime of the relevant metal-to-igandcharger-transfer (MLCT) state.

In this project, I have investigated the photoinduced structural changes of CAB2 in solution and it was shown to return to the ground state through the population of two excited states, a 3MLCT state and later a metal centered excited state (3MC) state. I also managed to confirm the DFT simulated structure of the 3MC structure, where the relevant bond lengths change 0.15 °A between ground state and the 3MC state. Furthermore, I was able to obtain a description of the combined solvation cage signal of both excited states through a singular value decomposition of the residual. The photoexcitation energy was shown to transfer very fast from solute to solvent which caused a temperature increase of the solvent at similar rates to the decay of the electronic states.

Finally, I was able to track the photoinduced structural dynamics in the 3MC state in real time. This dynamics was assigned to breathing mode vibrations of the 3MC state. The 3MC structure was varied in a breathing-like mode and fitted independently to each time delay. In this way, the vibrational amplitude was fitted to 0.035±0.003 °A and the oscillation period was found to be 290±6 fs, which is in excellent agreement with the theoretical estimate of 297 fs.

1[bis(2,6-bis(3-methylimidazol-1-ylidene)pyridine)iron(II)]2+