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

Journal Article · · Journal of Physical Chemistry Letters
 [1];  [2];  [3];  [4];  [5];  [1];  [1];  [6];  [1];  [1];  [5];  [5];  [7];  [8];  [8];  [8];  [8];  [9];  [10];  [5] more »;  [8];  [4] « less
  1. University of California, Berkeley, CA (United States)
  2. Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany)
  3. University of California, Berkeley, CA (United States); Complutense Univ. of Madrid (Spain)
  4. University of California, Berkeley, CA (United States); Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
  5. SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States). Photon Ultrafast Laser Science and Engineering Institute (PULSE)
  6. Naval Research Laboratory (NRL), Washington, DC (United States)
  7. SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States); Universität Duisburg Essen, Bochum (Germany); Technische Universität Dortmund, Bochum (Germany)
  8. SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)
  9. Bielefeld University (Germany)
  10. Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany); Christian-Albrechts-Universität zu Kiel (Germany)
+ Show Author Affiliations
Photoinduced biological and chemical reactions are often based on key structural transformations of a molecule driven across multiple electronic states. Acetylacetone (AcAc) is a prototypical system for complex chemical pathways involving several conical intersections (CI) and singlet–triplet intersystem crossings (ISC) characterized by distinct geometries. In the gas phase, AcAc is predominantly in a planar ring-like enolic form stabilized by a strong intramolecular O–H···O hydrogen bond. Following excitation into the S2 (ππ*) state at 266 nm, acetylacetone undergoes rapid internal conversion followed by intersystem crossing. Such relaxation pathways are associated with structural changes including ring opening, deplanarization, and bond elongation. In this work, ultrafast electron diffraction (UED) at the SLAC MeV-UED setup is employed as a direct structural probe with a time resolution of 160 fs. Together with trajectory surface hopping simulations, analysis of the UED data provides a new perspective on the early time nuclear dynamics in acetylacetone. Specifically, AcAc is observed to undergo ring opening, deplanarization, and bond elongation all within the first 700 fs after photoexcitation. The monitored dynamics is associated mainly with the nuclear motion on the S1 potential energy surface, formed after very rapid transfer from S2 to S1, allowing AcAc to reach the conical intersection to intersystem crossing. Such time scales of nuclear motion are contrasted with the time scales of electronic transitions in AcAc that were previously characterized with spectroscopic methods, specifically internal conversion (<100 fs) and intersystem crossing (∼1.5 ps).
Research Organization:
Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States); SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)
Sponsoring Organization:
Marie Sklodowska-Curie Actions (MSCA); National Science Foundation (NSF); US Department of Energy; USDOE Office of Science (SC), Basic Energy Sciences (BES); USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22), Chemical Sciences, Geosciences & Biosciences Division (SC-22.1); USDOE Office of Science (SC), Basic Energy Sciences (BES). Chemical Sciences, Geosciences & Biosciences Division (CSGB)
Grant/Contract Number:
AC02-05CH11231; AC02-76SF00515
OSTI ID:
2566299
Alternate ID(s):
OSTI ID: 2570155
OSTI ID: 2574642
Journal Information:
Journal of Physical Chemistry Letters, Journal Name: Journal of Physical Chemistry Letters Journal Issue: 20 Vol. 16; ISSN 1948-7185
Publisher:
American Chemical SocietyCopyright Statement
Country of Publication:
United States
Language:
English

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37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
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