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Internal conversion and intersystem crossing dynamics of uracil upon double thionation: a time-resolved photoelectron spectroscopy study in the gas phase
The photophysical properties of 2,4-dithiouracil (2,4-DTU) in the gas phase are studied by time-resolved photoelectron spectroscopy (TRPES) with three different excitation wavelengths in direct extension of previous work on uracil (U), 2-thiouracil (2-TU) and 4-thiouracil (4-TU). Non-radiative deactivation in the canonical nucleobases like uracil mainly occurs via internal conversion (IC) along singlet excited states, although intersystem crossing (ISC) to a long-lived triplet state was confirmed to play a minor role. In thionated uracils, ISC to the triplet state becomes ultrafast and highly efficient with a quantum yield near unity; however, the lifetime of the triplet state is strongly dependent on the position of the sulfur atom. In 2-TU, ISC back to the ground state occurs within a few hundred picoseconds, whereas the population remains trapped in the lowest triplet state in the case of 4-TU. Upon doubling the degree of thionation, ISC remains highly efficient and dominates the photophysics of 2,4-DTU. However, several low-lying excited states contribute to competing IC and ISC pathways and a complex deactivation mechanism, which is evaluated here based on TRPES measurements and discussed in the context of the singly thionated uracils.
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- Award ID(s):
- 1800050
- PAR ID:
- 10191443
- Date Published:
- Journal Name:
- Physical Chemistry Chemical Physics
- Volume:
- 22
- Issue:
- 27
- ISSN:
- 1463-9076
- Page Range / eLocation ID:
- 15608 to 15615
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/D0CP02145H
