Interdependent Electronic Structure, Protonation, and Solvatization of Aqueous 2‑Thiopyridone

2-Thiopyridone (2-TP),
a common model system for excited-state
proton transfer, has been simulated in aqueous solution with ab initio
molecular dynamics. The interplay of electronic structure, protonation,
and solvatization is investigated by comparison of three differently
protonated molecular forms and between the lowest singlet and triplet
electronic states. An interdependence clearly manifests in the mixed-character
T1 state for the 2-TP form, systematic structural distortions
of the 2-mercaptopyridine (2-MP) form, and photobase protolysis of
the 2-TP– form, in the aqueous phase. In comparison,
simplified continuum models for the solvatization are found to be
significantly inaccurate for several of the species. To facilitate
future computational studies, we therefore present a minimal representative
solvatization complex for each stable form and electronic state. Our
findings demonstrate the importance of explicit solvatization of the
compound and sets the stage for including it also in future studies.