Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 118, Issue 19, Pages -Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.2021714118
Keywords
ultrafast dynamics; femtosecond; X-ray scattering; charge transfer; & nbsp; excited state
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Funding
- US Department of Energy, Office of Science, Basic Energy Sciences [DESC0017995]
- NSF [CHE1953839]
- Engineering and Physical Sciences Research Council (EPSRC) [EP/V006819/1]
- Leverhulme Trust [RPG-2020-208]
- Carnegie Trust PhD Scholarship
- EPSRC PhD Studentship from the University of Edinburgh
- US Department of Energy, Office of Science, Office of Basic Energy Sciences [DEAC0276SF00515]
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The study tracks intramolecular charge transfer in N,N'-dimethylpiperazine using femtosecond gas-phase X-ray scattering, observing distinct charge-localized and charge-delocalized species and determining the molecular structure changes associated with them. The redistribution of electron density plays a key role in the charge transfer process.
Intramolecular charge transfer and the associated changes in molecular structure in N,N '-dimethylpiperazine are tracked using femtosecond gas-phase X-ray scattering. The molecules are optically excited to the 3p state at 200 nm. Following rapid relaxation to the 3s state, distinct charge-localized and charge-delocalized species related by charge transfer are observed. The experiment determines the molecular structure of the two species, with the redistribution of electron density accounted for by a scattering correction factor. The initially dominant charge-localized state has a weakened carbon-carbon bond and reorients one methyl group compared with the ground state. Subsequent charge transfer to the charge-delocalized state elongates the carbon-carbon bond further, creating an extended 1.634 angstrom bond, and also reorients the second methyl group. At the same time, the bond lengths between the nitrogen and the ring-carbon atoms contract from an average of 1.505 to 1.465 angstrom. The experiment determines the overall charge transfer time constant for approaching the equilibrium between charge-localized and charge-delocalized species to 3.0 ps.
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