Institut für Physik und Astronomie, Universität Potsdam, Karl-Liebknecht-Straße 24/25, 14476, Potsdam, Germany.
Department of Physics, Stockholm University, AlbaNova University Centre, 10691, Stockholm, Sweden.
Chemistry. 2019 Feb 1;25(7):1733-1739. doi: 10.1002/chem.201804166. Epub 2019 Jan 8.
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 and S states both relax promptly through intersystem crossing to the triplet T state. The T state, through its rapid population and near nanosecond lifetime, mediates nitrogen site deprotonation by ESPT in a secondary intersystem crossing to the S 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.
激发态质子转移 (ESPT) 是生物分子光化学中的一个基本过程，但其中介体往往难以直接观察到。我们通过瞬态 N 1s X 射线吸收光谱和多组态光谱模拟，确定了在水相 2-巯基吡啶中存在一种独特的 ESPT 途径。单重态 S 和 S 态的光激发都通过系间窜越迅速弛豫到三重态 T 态。T 态通过快速的布居和近纳秒的寿命，通过二次系间窜越到 S 势能面来介导氮位的质子转移。这明确确立了该体系在水溶液中的主要 ESPT 途径，这也与之前在乙腈中的测量结果相兼容。因此，解决了该化合物中 ESPT 途径的一些悬而未决的问题，包括其对激发波长和溶剂选择的可能依赖性。
