Daengngern, Rathawat

Preferred name

Alternative Name

Daengngern, R.

Main Affiliation

School of Science

rathawat.da@kmitl.ac.th

Now showing 1 - 10 of 33

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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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A theoretical investigation into the demethylation mechanism of dimethylsulfide over the W3O6 cluster
(2025-07-01)
Aziz, Hafiz Aji
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Kungwan, Nawee
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Gleeson, Duangkamol
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Saelee, Tinnakorn
;
Daengngern, Rathawat
Understanding how dimethyl sulfide (DMS) breaks down to form value-added products such as methanol on transition metal oxide catalysts is important for improving desulfurization processes. In this study, the reaction mechanism over a tungsten oxide cluster (W₃O₆) is elucidated using density functional theory (DFT) at the M06-L/LANL2DZ/aug-cc-pVTZ level of theory. Two competing mechanistic pathways were discovered over the W₃O₆ cluster: Pathway A) direct demethylation followed by methanol desorption and Pathway B) a water-assisted concerted demethylation pathway. Pathway A involves sequential steps with a moderate demethylation barrier (49.43 kcal/mol), but a significantly higher barrier (68.78 kcal/mol) for subsequent methanol formation, imposing a kinetic bottleneck. Remarkably, Pathway B, mediated by an explicit water molecule, facilitates a lower-barrier concerted transformation (56.19 kcal/mol), effectively bypassing the high-energy intermediate. Kinetic modeling via Transition State Theory and the Energetic Span Model reveal that despite the very low turnover frequency (TOF = 9.29 × 10−30 s⁻¹), the water-assisted pathway is energetically superior. These findings highlight the important role of water in helping the reaction proceed and offer insight for designing better catalysts for sulfur removal from DMS to methanol over the W₃O₆ cluster.
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Experimental and Theoretical Exploration of Ultrafast Excited State Double Proton Transfer in 2,5-Bis(2-benzimidazolyl)hydroquinone
(2025-07-01)
Prommin, Chanatkran
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Chaihan, Komsun
;
Daengngern, Rathawat
;
Mori, Seiji
;
Akutsu-Suyama, Kazuhiro
The electronic properties and excited-state intramolecular double proton transfer of 2,5-bis(2-benzimidazolyl)hydroquinone (bis-HBI) in a nonpolar solvent were investigated using a combined experimental and theoretical approach. Bis-HBI was successfully synthesized and its characterization was confirmed through 1H NMR and FT-IR. Three distinct emission peaks of bis-HBI were observed at 484, 597, and 730 nm, which were theoretically assigned to the di-enol (EE), mono-keto (EK), and di-keto (KK) species, respectively. The emission peaks at longer wavelengths (597 and 730 nm) are attributed to tautomerization upon photoexcitation and are assigned to the mono-keto and di-keto species, which result from multiple proton transfers. These species exhibit kinetically and thermodynamically favorable behaviors. On-the-fly dynamics simulations reveal that the double proton transfer process occurs ultrafast, within 433 fs. Additionally, both backward and forward proton transfers are observed during the first and second proton transfers, indicating tautomeric equilibria between the three species—EE, EK, and KK—on the excited-state surface. This is consistent with the potential energy surface along the proton transfer coordinate.
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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
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Daengngern, Rathawat
;
Sattayanon, Chanchai
;
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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Bodipy-pyridylhydrazone probe for fluorescence turn-on detection of fe3+ and its bioimaging application
(2021-07-01)
Nootem, Jukkrit
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Sattayanon, Chanchai
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Daengngern, Rathawat
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Kamkaew, Anyanee
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Wattanathana, Worawat
A novel pyridylhydrazone-tethered BODIPY (BODIPY-PH) was synthesized, fully characterized via nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopic (FTIR), and single-crystal X-ray diffraction (SC-XRD) techniques, and developed for the selective detection of Fe3+ through fluorescent enhancement process. This derivative showed 1:1 binding with Fe3+ in an acetonitrile-water mixture (1:9 v/v) with the binding constant (K) of 5.4 × 104 M−1 and the limit of detection of 0.58 µM. The Fe3+ complexation reaction has been proved to be a reversible process and could be effectively repeated up to three cycles. The electronic properties of BODIPY-PH and its Fe3+ complex modeled by the density functional theory (DFT) method suggested the presence of chelation-enhanced fluorescence (CHEF) effect in the Fe3+ binding reaction. The X-ray absorption spectroscopy (XAS) probed at Fe K-edge confirmed the complex formation between BODIPY-PH and the Fe3+ in an octahedral geometry. Finally, bioimaging against human embryonic kidney (Hek293) cell, through confocal fluorescence microscopic technique indicated that the BODIPY-PH displayed good permeability and low toxicity toward the tested cell lines and showed enhanced fluorescent signal in the cells incubated with Fe3+ proving its capability for Fe3+ analysis in cellular matrix.
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STRUCTURAL STABILITY AND SUBSTITUENT EFFECTS ON THE PHOTOPHYSICAL PROPERTIES OF THIOANISOLE EXPLORED BY EXCITED-STATE DYNAMIC SIMULATIONS
(2025-01-01)
Hongthong, Chatnicha
;
Daengngern, Rathawat
The photophysical properties of thioanisole (SCH3) and its derivatives as a representative system for investigating aryl sulfides were explored by TD-DFT using the B3LYP functional. Thioanisole appears in a variety of chemical applications due to its structural and reactive properties such as in dyes, drugs, and materials. Our investigations focus on the structural, photophysical, and dynamic properties influenced by substituents (F and Cl) on absorption and emission spectra. The electronic transition mainly corresponds to S<inf>0→S2</inf> (π→σ*) with excitation energies of 5.11 eV and 5.02 eV for SCH<inf>3F</inf> and SCH<inf>3Cl</inf>, respectively. The dynamic simulations on the first-excited state provide additional insights that complement those obtained from static calculations. The fluorescence spectrum of SCH3F typically shows a blue shift, while the fluorescence spectrum of SCH3Cl displays a red shift compared to SCH3. These findings indicate that the inductive effect plays a crucial role in structural stability, particularly influencing internal conversion during the dynamics, which may lead to a reduced fluorescence intensity.
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Bridging the Gap in Understanding the Mechanism of NH3 Formation During NO Reduction by CO in the Presence of H2O Over Rh/Al2O3 Catalysts: DFT Study
(2026-02-01)
Wangphon, Chanthip
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Khajondetchairit, Patcharaporn
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Rittiruam, Meena
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Ektarawong, Annop
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Alling, Björn
Ammonia (NH<inf>3</inf>) formation from nitric oxide (NO) and carbon monoxide (CO) in the presence of water is a promising pathway for low-temperature NO<inf>x</inf> reduction. In this work, density functional theory (DFT) calculations were used to investigate the mechanism of NH<inf>3</inf> formation on a Rh(111)/γ-Al<inf>2</inf>O<inf>3</inf>(110), in which the Rh(111) and γ-Al<inf>2</inf>O<inf>3</inf>(110) were considered separately. NO readily dissociates on the Rh site, forming N*, which reacts with CO to produce the key intermediate of NCO*. Meanwhile, water dissociates more easily on γ-Al<inf>2</inf>O<inf>3</inf>(110), providing H* species. The hydrolysis of NCO* can proceed via two pathways: on Rh(111), it forms HNCO, while on γ-Al<inf>2</inf>O<inf>3</inf>(110), it forms HNCOH*. Both intermediates subsequently decompose into NH* species, which are then hydrogenated to produce NH<inf>3</inf>. The Rh pathway is more favorable in both kinetics and thermodynamics, while the support mainly supplies hydrogen through water activation. These results suggest a dual-site mechanism in which Rh drives the main transformation, and γ-Al<inf>2</inf>O<inf>3</inf>(110) assists via hydrogen transfer. This work presents the individual roles of Rh and Al<inf>2</inf>O<inf>3</inf> surfaces in NO reduction with CO, producing NH<inf>3</inf>, which is relevant to catalytic behavior under humid conditions.
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Physico-chemical characterization of natural lake pigments obtained from Caesalpinia Sappan Linn. and their composite films for poly(lactic acid)-based packaging materials
(2018-10-01)
Girdthep, Sutinee
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Sirirak, Jitnapa
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Daranarong, Donraporn
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Daengngern, Rathawat
;
Chayabutra, Supanee
A newly colored biodegradable PLA-based film was fabricated from a compatibilized poly(lactic acid) poly(butylene adipate-co-terephthalate) blend (PLA/PBAT/TBT) using the natural lake pigment of Sappan. The natural lake pigment of Sappan was prepared as a Sappan colorant-adsorbed kaolinite (S-KT). S-KT composite in the form of an insoluble pigment and was prepared via co-precipitation and adsorption under basic conditions. It had a pinkish-red color and a maximum absorption of 516 nm. The stability of the natural lake pigment was improved and was confirmed by the improvement of the initial and maximum degradation temperatures from the TGA results, which could be attributed to the electrostatic attraction due to the process of chelation. The chelation that occurred between the Al(III) ion, the oxygen atoms of kaolinite surface and the brazilein molecules was proposed. The influence of S-KT content in the compatibilized blended films, known as S-KT composite films, was investigated by comparison with the KT composite film and the film without fillers. When the content of S-KT increased, the S-KT composite films exhibited a darker pinkish-red color. The mechanical properties in terms of strength increased due to KT acting as a nucleating agent with a 92% increase in the heat of crystallization in the S-KT7 film when compared with the film without fillers. The exfoliated-intercalated structure of S-KT resulted from the KT platelet disaggregation by brazilein adsorption and the intercalating of Al3+cations chelation as a hybrid interaction on the KT surface, which was indicated by the SEM. In addition, S-KT composite film could effectively resist heat at high temperatures with the maximum degradation temperature ranging from 337 to 393° C. This occurred as a result of KT clay acting as a superior insulator. Based on these results, the natural lake pigments presented the potential to be employed in the biodegradable polymer and could be used as a substitute for more toxic pigments. The biodegradable PLA-based colored films described here have a potential to be used in packaging applications. They offer the potential to increase the value-added appeal of products, with the benefit of being considered environmentally friendly by the consumer.
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Theoretical Prediction and Analysis of the UV/Visible Absorption and Emission Spectra of Chiral Carbon Nanorings
(2018-09-20)
Daengngern, Rathawat
;
Camacho, Cristopher
;
Kungwan, Nawee
;
Irle, Stephan
UV/vis absorption and emission spectra of recently synthesized chiral carbon nanorings were simulated using first-principles-based molecular dynamics and time-dependent density functional theory (TD-DFT). The chiral carbon nanorings are derivatives of the [n]cycloparaphenylene ([n]CPP) macrocycles, containing an acene unit such as naphthalene, ([n]CPPN), anthracene ([n]CPPA), and tetracene ([n]CPPT), in addition to n paraphenylene units. In order to study the effect of increasing molecular size on absorption and emission spectra, we investigated the cases where n = 6 and 8. Frontier molecular orbital analysis was carried out to give insight into the degree of excitation delocalization and its relationship to the predicted absorption spectra. The lowest excited singlet state S<inf>1</inf> corresponds to a HOMO-LUMO π-π∗ transition, which is allowed in all chiral carbon nanorings due to lack of molecular symmetry, in contrast to the forbidden HOMO-LUMO transition in the symmetric [n]CPP molecules. The S<inf>1</inf> absorption peak exhibits a blue-shift with increasing number of paraphenylene units in particular for [n]CPPN and [n]CPPA and less so in the case of [n]CPPT. In the case of CPPN and CPPA, the transition density is mainly localized over a semicircle of the macrocycle with the acene unit in its center but is strongly localized on the tetracene unit in the case of CPPT. Molecular dynamics simulations performed on the excited state potential energy surfaces reveal red-shifted emission of these chiral carbon nanorings when the size of the π-conjugated acene units is increased, although the characteristic [n]CPP blue-shift with increasing paraphenylene unit number n remains apparent. The anomalous emission blue-shift is caused by the excited state bending and torsional motions that stabilize the π HOMO and destabilize the π∗ LUMO, resulting in an increasing HOMO-LUMO gap.
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Molecular design of benzo[c][1,2,5]thiadiazole or thieno[3,4-d]pyridazine-based auxiliary acceptors through different anchoring groups in D-π-A-A framework: A DFT/TD-DFT study
(2022-06-01)
Marlina, Lala Adetia
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Haryadi, Winarto
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Daengngern, Rathawat
;
Pranowo, Harno Dwi
Based on density functional theory (DFT) and time-dependent DFT (TD-DFT) methods, a novel series of D-π-A-A porphyrin sensitizers adsorbed on the TiO<inf>2</inf> cluster has been investigated. The D-π-A-A configurations contained a donor of iminodibenzyl, π-linker of Zn-porphyrin, and two kinds of auxiliary acceptors (labeled as BT and TP), as well as five types of anchoring groups. The ground-state geometries, electronics, optics, and charge transfer properties of all free dyes including injection driving force (ΔGinj), regeneration energy (ΔGreg), and light-harvesting efficiency (LHE) were calculated. Additionally, reorganization energy (λ<inf>total</inf>), electron affinity (EA), and ionization potential (IP) were also reported to confirm the transport properties of the designed dye. Furthermore, the interfacial system of dye@(TiO<inf>2</inf>)<inf>48</inf> was further discussed to reveal the complexation energy of the system by considering the adsorption energy (E<inf>ads</inf>) between dyes and (TiO<inf>2</inf>)<inf>48</inf>. The results showed that the insertion of different auxiliary acceptors in the D-π-A-A motif and variations in the anchoring groups resulted in red-shift absorption along with the increase in photovoltaic properties. These results suggested that BT with the rhodanine-3-acetic acid group (BT4) and BT with 2-(1,1-dicyanomethylene)rhodanine group (BT5) and TP with the same rhodanine-3-acetic acid and 2-(1,1-dicyanomethylene)rhodanine groups (TP4 and TP5) had shown better properties among other candidates for DSSCs. BT4-BT5 and TP4-TP5 had pronounce effect on optical and charge transfer properties by showing small HOMO-LUMO gaps, red-shifted spectra (λ<inf>max</inf>), greater LHE and ICT characters, and maximum-negative E<inf>ads</inf>. Thus, our theoretical investigation using these auxiliary moieties can be helpful for the precise structural modifications and design for developing efficient dyes in dye-sensitized solar cells (DSSCs).

Daengngern, Rathawat

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