Capturing Ring Opening in Photoexcited Enolic Acetylacetone upon Hydrogen Bond Dissociation by Ultrafast Electron Diffraction

Valeriu Scutelnic, Denis S. Tikhonov, Sonia Marggi Poullain, E. A. Haugen, A. Attar, L. Barreau, K. Chang, A. P. Fidler, J. D. Gaynor, Y.-C. Lin, J. Yang, Elio Champenois, X. Wang, X. Shen, D. Luo, F. Ji, S. Weathersby, Y. V. Vishnevskiy, M. Schnell, Thomas Wolf, M.-F. Lin, S. R. Leone
May 2025
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Abstract

The study focuses on the structural transformations of acetylacetone (AcAc) after being excited by a laser. In the gas phase, this molecule exists in a stable, ring-like enolic form due to a strong internal hydrogen bond. Using ultrafast electron diffraction (UED) with a time resolution of 160 femtoseconds, the researchers were able to directly observe the molecule’s structural changes. Following photoexcitation, the molecule undergoes several rapid changes, including ring opening, deplanarization, and bond elongation, all occurring within the first 700 femtoseconds. These structural dynamics are primarily associated with the nuclear motion on the S1 potential energy surface, which is reached after a very rapid internal conversion from the S2 state. The experiment provides insight into the timescales of these nuclear motions, which are compared to the previously known electronic transition timescales.

Type
Journal article
Publication
The Journal of Physical Chemistry Letters
Elio Champenois
Elio Champenois
Sr. Staff Systems Scientist, ASML
Thomas Wolf
Thomas Wolf
Staff Scientist

My research is focused on discovering structure-function relationships in ultrafast photochemistry to better understand and eventually control this type of reactions.