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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.
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Excited-state intramolecular proton transfer reactions of 2,5-bis(2′-benzoxazolyl)hydroquinone and its water cluster exhibiting single and double proton transfer: A TD-DFT dynamics simulation
(2019-07-15)
Daengngern, Rathawat
;
Salaeh, Rusrina
;
Saelee, Tinnakorn
;
Kerdpol, Khanittha
;
Kungwan, Nawee
Detailed pictures of the excited-state intramolecular proton transfer (ESIPT)of 2,5-bis(2′-benzoxazolyl)hydroquinone (BHQ)and its water cluster have been investigated by dynamics simulations on the first lowest-excited energy using time-dependent density functional theory (TD-DFT). We focused on the structural, photophysical and dynamic properties of BHQ in the absence and presence of water molecules through intermolecular hydrogen bonds (interHBs). Our dynamics simulations reveal three possible mechanisms of the ESIPT processes: i)no proton transfer (No PT); ii)single PT (SPT); and iii)double PT (DPT), that could take place within the PT time of 160 fs via intrinsic intramolecular hydrogen bonds (intraHBs). The ESIPT mechanism of isolated BHQ elucidates that back PT is likely to be found at 64% rather than the SPT (32%)and DPT (4%), which is in good agreement with the experiments of dual fluorescence from di-enol and mono-keto emissions. Notably, the results from BHQ with water (BHQ-(H<inf>2</inf>O)<inf>2</inf>)reveal that the participation of water might produce a remarkable effect on promoting the SPT process up to 60% and DPT up to 7 times when compared to conditions of no water. The simulated probability of PT is well related to possible PT mechanisms regarding different tautomers in the fluorescence spectra found in previous experiments. The existence of di-keto tautomer arose from the DPT of BHQ and its water cluster and was not observed in the UV/Vis spectrum.
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The effect of protic solvents on the excited state proton transfer of 3-hydroxyflavone: A TD-DFT static and molecular dynamics study
(2018-02-01)
Salaeh, Rusrina
;
Prommin, Chanatkran
;
Chansen, Warinthon
;
Kerdpol, Khanittha
;
Daengngern, Rathawat
The effect of intermolecular hydrogen bonding played by protic solvents (ammonia, methanol and water) on the excited state proton transfer (ESPT) reaction of 3-hydroxyflavone (3HF) was theoretically investigated using density functional theory (DFT) and time-dependent DFT (TD-DFT). The formation of intermolecular hydrogen bond induced by protic solvents indicates that the intramolecular hydrogen bond may be interrupted in favor of a complex causing low quantum yield of keto emission and exhibiting dual emission (both enol and keto) in experiment. The strengthening of intermolecular hydrogen bond in the S<inf>1</inf> state has been confirmed by the red-shift of IR vibrational spectra and shorter bond distances involving proton transfer (PT) process in comparison with those of the S<inf>0</inf> state. From potential energy curves (PECs) of PT coordinate, PT process is likely to proceed in S<inf>1</inf> state and PT in 3HF(NH<inf>3</inf>) occurs more easily than those of 3HF(CH<inf>3</inf>OH) and 3HF(H<inf>2</inf>O) due to its lower barrier. Moreover, on-the-fly dynamics simulations of all complexes were carried out to provide the detailed information on the PT mechanism. The dynamic results show that ESPT process of 3HF with protic solvent takes place through intermolecular hydrogen bond with slower PT time (259, 117 and 104 fs for 3HF(NH<inf>3</inf>), 3HF(CH<inf>3</inf>OH) and 3HF(H<inf>2</inf>O), respectively) than that of 3HF (76 fs) via intramolecular hydrogen bond. Furthermore, the ultrafast PT time is found to be nicely correlated with polarity of solvent and PT probability is also anti-correlated with PT barrier.

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