title: Solvent effects on the ultrafast nonradiative deactivation mechanisms of thymine in aqueous solution: excited-state QM/MM molecular dynamics simulations.
abstract: On-the-fly excited-state quantum mechanics/molecular mechanics molecular dynamics (QM/MM-MD) simulations of thymine in aqueous solution are performed to investigate the role of solvent water molecules on the nonradiative deactivation process. The complete active space second-order perturbation theory (CASPT2) method is employed for a thymine molecule as the QM part in order to provide a reliable description of the excited-state potential energies. It is found that, in addition to the previously reported deactivation pathway involving the twisting of the C-C double bond in the pyrimidine ring, another efficient deactivation pathway leading to conical intersections that accompanies the out-of-plane displacement of the carbonyl group is observed in aqueous solution. Decay through this pathway is not observed in the gas phase simulations, and our analysis indicates that the hydrogen bonds with solvent water molecules play a key role in stabilizing the potential energies of thymine in this additional decay pathway.
authors: Department of Chemistry, Faculty of Science, Hokkaido University, Sapporo 060-0810, Japan.
authors: Akira
authors: A
authors: Nakayama
authors: Gaku
authors: G
authors: Arai
authors: Shohei
authors: S
authors: Yamazaki
authors: Tetsuya
authors: T
authors: Taketsugu
mesh_terms: D005740:Gases / Q000737:chemistry; D056004:Molecular Dynamics Simulation; D011789:Quantum Theory; D013816:Thermodynamics; D013941:Thymine / Q000737:chemistry*; D014867:Water / Q000737:chemistry*
chemical_list: D005740:Gases; D014867:Water; D013941:Thymine