期刊
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
卷 140, 期 47, 页码 16087-16093出版社
AMER CHEMICAL SOC
DOI: 10.1021/jacs.8b07057
关键词
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资金
- European Research Council Advanced Grant STRATUS [291198]
- Marie Curie actions (FP7-PEOPLE-IEF-2012)
- H2020 Grant [765266]
- Fapemig
- CNPq
- CAPES
We combined sub-30 fs broadband transient absorption spectroscopy in the ultraviolet with state-of-the-art quantum mechanics/molecular mechanics simulations to study the ultrafast excited-state dynamics of the sulfur-substituted nucleobase 4-thiouracil. We observed a clear mismatch between the time scales for the decay of the stimulated emission from the bright pi pi* state (76 +/- 16 fs, experimentally elusive until now) and the buildup of the photoinduced absorption of the triplet state (225 +/- 30 fs). These data provide evidence that the intersystem crossing occurs via a dark state, which is intermediately populated on the sub-100 fs time scale. Nonlinear spectroscopy simulations, extrapolated from a detailed CASPT2/MM decay path topology of the solvated system together with an excited state mixed quantum-classical nonadiabatic dynamics, reproduce the experimental results and explain the experimentally observed vibrational coherences. The theoretical analysis rationalizes the observed different triplet buildup times of 4- and 2-thiouracil.
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