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T 1 Population as the Driver of Excited‐State Proton‐Transfer in 2‐Thiopyridone
Author(s) -
Eckert Sebastian,
Norell Jesper,
Jay Raphael M.,
Fondell Mattis,
Mitzner Rolf,
Odelius Michael,
Föhlisch Alexander
Publication year - 2019
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201804166
Subject(s) - intersystem crossing , chemistry , excited state , photochemistry , singlet fission , singlet state , ultrafast laser spectroscopy , deprotonation , population , aqueous solution , nanosecond , proton , acetonitrile , triplet state , spectroscopy , atomic physics , physics , ion , laser , demography , organic chemistry , quantum mechanics , sociology , optics , chromatography
Excited‐state proton transfer (ESPT) is a fundamental process in biomolecular photochemistry, but its underlying mediators often evade direct observation. We identify a distinct pathway for ESPT in aqueous 2‐thiopyridone, by employing transient N 1s X‐ray absorption spectroscopy and multi‐configurational spectrum simulations. Photoexcitations to the singlet S 2 and S 4 states both relax promptly through intersystem crossing to the triplet T 1 state. The T 1 state, through its rapid population and near nanosecond lifetime, mediates nitrogen site deprotonation by ESPT in a secondary intersystem crossing to the S 0 potential energy surface. This conclusively establishes a dominant ESPT pathway for the system in aqueous solution, which is also compatible with previous measurements in acetonitrile. Thereby, the hitherto open questions of the pathway for ESPT in the compound, including its possible dependence on excitation wavelength and choice of solvent, are resolved.