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Author: search.filters.author.Kungwan, NaweeSubject: search.filters.subject.Dynamics simulation

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    Tautomeric enhancement of 2-(1H-pyrazol-5-yl)pyridine in photoinduced proton transfer by water-assisted molecules
    (2024-09-20)
    Salaeh, Rusrina
    ;
    Inporn, Wutthana
    ;
    Chansen, Warinthon
    ;
    Kungwan, Nawee
    ;
    Daengngern, Rathawat
    Theoretical insight of excited state proton transfer (ESPT) in 2-(1H-pyrazol-5-yl)pyridine abbreviated as PPP interacting with water wires: PPP(H<inf>2</inf>O)<inf>n</inf> where n = 1–3 has been presented in both static and dynamics studies. Explicit water molecules placed around PPP have been simulated to elucidate the intermolecular hydrogen bonding interactions between them. Hydrogen bond strengthening in the excited state (S<inf>1</inf>) has been verified by shorter bond distances and redshift of IR vibrational spectra involving the proton transfer (PT) process. Furthermore, on-the-fly excited state dynamics simulations of all complexes have been performed to provide detailed information on the PT mechanism. The dynamic results show that one water molecule added to the neighboring PPP as an intermolecular hydrogen bonding bridge can promote double excited state intermolecular proton transfer up to 36% compared with its intrinsic intramolecular hydrogen bond of the PPP system. Meanwhile adding a second or third water molecule could decrease the probabilities of PT. Especially in PPP(H<inf>2</inf>O)<inf>3</inf>, a rearrangement of water molecules is observed that PT occurs via one water molecule. Hence, the models with explicit water molecules interacting with PPP as intermolecular hydrogen bonding bridge are a great representative role played by water molecules of the PT process at the molecular level.
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    Dynamics simulation of excited-state proton transfer reactions of 8-hydroxyquinoline with water clusters: A TD-DFT study
    (2023-08-01)
    Kerdpol, Khanittha
    ;
    Daengngern, Rathawat
    ;
    Kungwan, Nawee
    Detailed pictures of the excited-state proton transfer reactions of 8-hydroxyquinoline (8HQ) and its small clusters of water have been systematically investigated using density functional theory (DFT) and time-dependent DFT (TD-DFT) methods at B3LYP/TZVP and TD-B3LYP/TZVP level of theory, respectively. Intramolecular hydrogen bond (intraHB) and intermolecular hydrogen bond (interHB) interactions between 8HQ and water cluster become stronger in the first excited state (S<inf>1</inf>), confirmed by hydrogen bond distances and topological analysis. In addition, TD-B3LYP dynamics simulations have been elucidated and revealed that excited-state intramolecular proton transfer (ESIntraPT) and multiply excited-state intermolecular proton transfer (ESInterPT) reactions of these complexes can take place in the ultrafast time scale of femtoseconds. Increasing the number of water molecules may give rise to a barrier energy that is anti-correlated to the probability of tautomer species from phototautomerization, especially in 8HQ-W<inf>1</inf> and 8HQ-W<inf>1+1</inf>. Moreover, water molecules initiate multiple proton transfer occurring through two- and three-step ESInterPT namely excited-state double proton transfer (ESDPT) and excited-state triple proton transfer (ESTPT) in which the interHBs are formed by rearrangement of water molecules of 8HQ-W<inf>2</inf>. This circumstance takes a longer time (up to 470 fs) compared to that of ESIntraPT. Thus, the simulated results from this study could provide insight into ESIntraPT and ESInterPT of phototautomerization and the significant photodynamics which could not be found from the experimental aspects of 8HQ and its solvent clusters.