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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
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Inporn, Wutthana
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Chansen, Warinthon
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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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Proton exchange of carbonic acid and methylamine complex accelerated by a single-water molecule via intermolecular hydrogen bonding: A theoretical investigation
(2024-06-01)
Panbo, Pakuna
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Payaka, Apirak
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Salaeh, Rusrina
;
Daengngern, Rathawat
A theoretical investigation of the microsolvation effect on proton exchange (PE) between carbonic acid and methylamine (CA-MTA) has been explored by quantum dynamics simulations. The structural, energy, and dynamic properties of the CA-MTA complex with and without an explicit water molecule are elucidated at the molecular level. The reactions from this study have been clarified into different types: single-step PE (SSPE) and stepwise PE (SWPE). Without the water molecule, the SSPE mechanism is hardly found but observable with a low probability of 0.2. In particular, the water molecule interacting through intermolecular hydrogen-bonded network between CA and MTA in CA-MTA-W<inf>in</inf> could affect PE by showing both SSPE and SWPE mechanisms. In addition, the existing water molecule plays the significant role in shortening intermolecular hydrogen bonding interactions within the complex resulting in increasing the probability of PE up to 0.92 especially in CA-MTA-W<inf>out</inf>. Hence, one water molecule could be used to provide reliable results to represent the significant activity that occurs for the proton exchangeability of the CA and MTA complex.
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Theoretical insights into ultrafast excited state proton transfer coupled with twisted intramolecular charge transfer mechanism in 7-(2ʹ-pyridyl)indole: Effect of hydrogen bonding
(2023-10-15)
Salaeh, Rusrina
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Daengngern, Rathawat
The ultrafast proton transfer (PT) process in the excited state of 7-(2′-pyridyl)indole (abbreviated as 7PyIn) has been elucidated by on-the-fly dynamics simulations using the algebraic-diagrammatic construction scheme of second order (ADC(2)) method under the resolution of identity (RI) approximation. The tautomers of 7PyIn alone and associated with an acetonitrile molecule in the 7PyIn-CH<inf>3</inf>CN complex are most likely found after the excited state intramolecular proton transfer (ESIntraPT) within an ultrafast time scale between 40 and 60 fs. While a methanol molecule in the complex of 7PyIn-CH<inf>3</inf>OH could establish both ESIntraPT and excited-state intermolecular proton transfer (ESInterPT). ESInterPT of 7PyIn-CH<inf>3</inf>OH possibly occurs through a concerted process via the intermolecular hydrogen bonding bridge of the methanol molecule almost twice faster than that of ESIntraPT. This slower circumstance of the ESIntraPT process found in 7PyIn-CH<inf>3</inf>OH may be caused by the competition between formations of the intramolecular and intermolecular hydrogen bonds between 7PyIn and methanol. In addition, after the accomplishment of excited state proton transfer (ESPT), the initiation of conical intersection could be taking place by the structural twist of 7PyIn. The geometries, energies, proton probabilities, and provided mechanisms via the dynamics simulations of 7PyIn and its solvent clusters exhibiting ESIntraPT and ESInterPT are explored to provide the dynamic pictures of the ESPT processes at the molecular level.
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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
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Salaeh, Rusrina
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Saelee, Tinnakorn
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Kerdpol, Khanittha
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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
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Prommin, Chanatkran
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Chansen, Warinthon
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Kerdpol, Khanittha
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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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Theoretical Insights on Solvent Control of Intramolecular and Intermolecular Proton Transfer of 2-(2′-Hydroxyphenyl)benzimidazole
(2017-08-10)
Prommin, Chanatkran
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Kanlayakan, Narissa
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Chansen, Warinthon
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Salaeh, Rusrina
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Kerdpol, Khanittha
Excited-state proton transfer (ESPT) processes of 2-(2′-hydroxyphenyl)benzimidazole (HBI) and its complexation with protic solvents (H<inf>2</inf>O, CH<inf>3</inf>OH, and NH<inf>3</inf>) have been investigated by both static calculations and dynamics simulations using density functional theory (DFT) at B3LYP/TZVP theoretical level for ground state (S<inf>0</inf>) and time-dependent (TD)-DFT at TD-B3LYP/TZVP for excited state (S<inf>1</inf>). For static calculations, absorption and emission spectra, infrared (IR) vibrational spectra of O-H mode, frontier molecular orbitals (MOs), and potential energy curves (PECs) of proton transfer coordinate were analyzed. Simulated absorption and emission spectra show an agreement with available experimental data. The hydrogen bond strengthening in the S<inf>1</inf> state has been proved by the changes of IR vibrational spectra and bond parameters of the hydrogen moiety with those of the S<inf>0</inf> state. The MOs provide the visual electron density redistribution confirming the hydrogen bond strengthening mechanism. The PECs show that the proton transfer (PT) process is easier to occur in the S<inf>1</inf> state than the S<inf>0</inf> state. Moreover, on-the-fly dynamics simulations of all systems were carried out to provide the detailed information on time revolution. The results revealed that the excited-state intermolecular proton transfer for HBI is fast, whereas the excited-state intermolecular proton transfer for HBI with protic solvents are slower than that of HBI because the competition between intra- and intermolecular hydrogen-bonds between HBI and protic solvent. These intermolecular hydrogen-bonds hinder the formation of tautomer, hence explaining the low quantum yield found in the protic solvent experiment. Especially for HBI complexing with methanol, only ESIntraPT occurs with small probability compared to HBI with water and ammonia.
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Theoretical study on influence of geometry controlling over the excited-state intramolecular proton transfer of 10-hydroxybenzo[h]quinoline and its derivatives
(2017-08-01)
Chansen, Warinthon
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Salaeh, Rusrina
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Prommin, Chanatkran
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Kerdpol, Khanittha
;
Daengngern, Rathawat
A structural modification on quinoline as a proton donor of 10-hydroxybenzo[h]quinoline (HBQ) giving different HBQ derivatives greatly affects their photophysical properties. In this study, the excited-state intramolecular proton transfer (ESIPT) reactions of HBQ and its derivatives with different geometries have been systematically investigated using DFT and TD-DFT at B3LYP/TZVP. Calculated absorption and emission spectra are used to describe the photophysical changes in which the absorption spectra of HBQ derivatives are blue-shifted compared with that of HBQ while their emission spectra are blue-shifted except those of 3,4-dihydro indene[1,2-b]pyrrole-8-ol (IPRO) and 2-(4H-pyrrol-2-yl)phenol (PRP) compounds with different proton donor and connecting moiety are red-shifted. From results of potential energy curves along the proton transfer (PT) coordinate, PT is favorable in the excited-state but not in the ground state. On-the-fly dynamics simulations in the excited-state are further employed to determine reaction mechanisms and the time evolution of PT. The ESIPT process easily occurs in most of the compounds except the IPRO with much high PT barrier. The ESIPT times in most compounds take place within 100 fs and PT probability is nicely anti-correlated with the PT barrier. Thus, the geometry changes alter the electronic spectra but do not affect ESIPT of HBQ derivatives. Moreover, once the PT is complete, the internal conversion is initiated by twisted skeleton, leading to lower intensity of tautomer emission.

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