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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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Effect of water microsolvation on the excited-state proton transfer of 3-hydroxyflavone enclosed in -cyclodextrin
(2021-02-02)
Kerdpol, Khanittha
;
Daengngern, Rathawat
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Sattayanon, Chanchai
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Namuangruk, Supawadee
;
Rungrotmongkol, Thanyada
The effect of microsolvation on excited-state proton transfer (ESPT) reaction of 3-hydroxyflavone (3HF) and its inclusion complex with -cyclodextrin (-CD) was studied using computational approaches. From molecular dynamics simulations, two possible inclusion complexes formed by the chromone ring (C-ring, Form I) and the phenyl ring (P-ring, Form II) of 3HF insertion to -CD were observed. Form II is likely more stable because of lower fluctuation of 3HF inside the hydrophobic cavity and lower water accessibility to the encapsulated 3HF. Next, the conformation analysis of these models in the ground (S0) and the first excited (S1) states was carried out by density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations, respectively, to reveal the photophysical properties of 3HF influenced by the -CD. The results show that the intermolecular hydrogen bonding (interHB) between 3HF and -CD, and intramolecular hydrogen bonding (intraHB) within 3HF are strengthened in the S1 state confirmed by the shorter interHB and intraHB distances and the red-shift of O-H vibrational modes involving in the ESPT process. The simulated absorption and emission spectra are in good agreement with the experimental data. Significantly, in the S1 state, the keto form of 3HF is stabilized by -CD, explaining the increased quantum yield of keto emission of 3HF when complexing with -CD in the experiment. In the other word, ESPT of 3HF is more favorable in the -CD hydrophobic cavity than in aqueous solution.
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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
;
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
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Prommin, Chanatkran
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Chansen, Warinthon
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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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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
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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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Heteroatom effect on photophysical properties of 2-(2′-hydroxyphenyl)benzimidazole and its derivatives as fluorescent dyes: A TD-DFT study
(2017-08-01)
Manojai, Natthaporn
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Daengngern, Rathawat
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Kerdpol, Khanittha
;
Ngaojampa, Chanisorn
;
Kungwan, Nawee
The effects of hetero nitrogen substitution on the photophysical properties and excited-state intramolecular proton transfer (ESIPT) of HBX derivatives (HBI, HBO and HBT where X=NH, O and S, respectively) were investigated using density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations at B3LYP/6-311+G(d,p) level, which is the suitable method of choice validated from various density functionals. Geometries and absorption spectra of all derivatives as well as emission spectra of selected derivatives were calculated at the same level of theory. The hetero nitrogen substitution of HBX resulted in the red shift emission spectra, which implies that the lone pair of electron in the substituted nitrogen has the effect on the π-conjugated system. In addition, results of frontier molecular orbital analysis show that vertical S<inf>0</inf>→S<inf>1</inf> transition of these molecules corresponds essentially to the excitation from HOMO (π) to LUMO (π*). The potential energy curves (PECs) of selected derivatives were used to investigate the occurrence of ESIPT and the chance was found in this order: HBT>HBI>HBO. The hetero nitrogen substituted on 1,4 and 3,4 position of HBX derivatives could easily facilitate the ESIPT process, because the nitrogen substitution makes O–H bond of selected HBX derivatives weaker than those of other derivatives and the hydrogen bond in N–H becomes stronger in the excited state, resulting in lower PT barrier. The obtained information of the electronic structure, the photophysical property and the chance of ESIPT of hetero nitrogen substituted HBX molecules is useful for molecular design of fluorescent molecular probes.

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