Direct Observation of the <i>ππ*</i> to <i>nπ*</i> Transition in 2-Thiouracil via Time-Resolved NEXAFS Spectroscopy
The photophysics of nucleobases has been the subject of both theoretical and experimental studies over the past decades due to the challenges posed by resolving the steps of their radiationless relaxation dynamics, which cannot be described in the framework of the Born-Oppenheimer approximation (BOA). In this context, the ultrafast dynamics of 2-thiouracil has been investigated with a time-resolved NEXAFS study at the Free Electron Laser FLASH. Near Edge X-ray Absorption Fine Structure spectroscopy (NEXAFS) can be used to observe electronic transitions in ultrafast molecular relaxation. We performed time-resolved UV-pump/X-ray probe absorption measurements at the sulfur 2<i>s</i> (L1) and 2<i>p</i> (L2/3) edges. We are able to identify absorption features corresponding to the S2 (<i>ππ*</i>) and S1 (<i>nπ*</i>) electronic states. We observe a delay of 102 ± 11 fs in the population of the <i>nπ*</i> state with respect to the initial optical excitation and interpret the delay as the time scale for the S2 → S1 internal conversion. We furthermore identify oscillations in the absorption signal that match a similar observation in our previous X-ray photoelectron spectroscopy study on the same molecule.
Authors
- Markus Gühr
- Jan Metje
- S. Düsterer (ORCID: https://orcid.org/0000-0003-4379-1327)
- M. S. Robinson (ORCID: https://orcid.org/0000-0003-3891-6375)
- Richard J. Squibb (ORCID: https://orcid.org/0000-0001-6708-8631)
- Fabiano Lever (ORCID: https://orcid.org/0000-0002-8448-7594)
- S. Ališauskas (ORCID: https://orcid.org/0000-0002-7033-4087)
- David Picconi (ORCID: https://orcid.org/0000-0001-6468-1595)
- Andrea Trabattoni (ORCID: https://orcid.org/0000-0002-0187-9075)
- Peter Saalfrank (ORCID: https://orcid.org/0000-0002-5988-5945)
- Francesca Calegari (ORCID: https://orcid.org/0000-0003-3234-7298)
- R. Feifel (ORCID: https://orcid.org/0000-0001-5234-3935)
- Tommaso Mazza (ORCID: https://orcid.org/0000-0003-0434-8533)
- Thomas Wolf (ORCID: https://orcid.org/0000-0002-0641-1279)
- Dennis Mayer (ORCID: https://orcid.org/0000-0002-1858-6818)
- Matthew R. Ware (ORCID: https://orcid.org/0000-0002-7006-0004)
- Marion Kuhlmann
Institutions
- Leibniz University Hannover (DE)
- University of Potsdam (DE)
- Deutsches Elektronen-Synchrotron DESY (DE)
- SLAC National Accelerator Laboratory (US)
- Hamburg Centre for Ultrafast Imaging
- Heinrich Heine University Düsseldorf (DE)
- University of Gothenburg (SE)
- European X-Ray Free-Electron Laser (DE)
Publication Details
- Journal
- The Journal of Physical Chemistry Letters
- Published
- 2025-04-15
- DOI
- https://doi.org/10.1021/acs.jpclett.5c00544
- Citations
- 1
- Primary Topic
- Advanced Chemical Physics Studies
- Type
- article
- Field-Weighted Citation Impact
- 1.25
Funders
- Deutsche Forschungsgemeinschaft
- Volkswagen Foundation
- Helmholtz Association
- Basic Energy Sciences
- H2020 European Research Council