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New insights into ESIPT mechanism of three sunscreen compounds in solution: A combined experimental and theoretical study
Abstract
In this present work, we have successfully designed and investigated three flavonoid sunscreen compounds. Based on steady-state spectroscopy and time-dependent density functional theory (TDDFT), the mechanism of excited state intramolecular proton transfer (ESIPT) of sunscreen compounds was studied. The calculated UV-Vis absorption spectra and fluorescence emission spectra are in good agreement with the experimental results in methanol solution. The potential energy curve demonstrates that the ESIPT process can easily occur in the three sunscreen compounds without energy barrier. Therefore, the absorbed excitation energy can get back to the ground state through a non-radiative relaxation process. Light stability tests ensure that the three flavonoids have the potential as sunscreens. This work provides not only an application of the ESIPT process in sunscreen mechanisms, but also a theory basis for the development of novel sunscreen molecules.
... The maxima of the fluorescence (FL) spectra, measured on the same solutions using the excitation wavelength of 370 nm, were found at approximately 480 nm for solutions in methanol and in Tris-HCL buffer, and at 470 nm for solutions in methanolwater. The absorption wavelength of L solutions in methanol was found at 349 nm [9,13] and at 402 nm for solutions in alkaline methanol-water [14]. The FL emission intensity of L solutions has been reported to be very small [14,15]; nonetheless, the FL maxima were found at approximately 420 nm in methanol solution when an excitation wavelength of 355 nm was used [13], and at 520 nm in alkaline methanol-water solution when using an excitation wavelength of 384 nm [14]. ...
... The absorption wavelength of L solutions in methanol was found at 349 nm [9,13] and at 402 nm for solutions in alkaline methanol-water [14]. The FL emission intensity of L solutions has been reported to be very small [14,15]; nonetheless, the FL maxima were found at approximately 420 nm in methanol solution when an excitation wavelength of 355 nm was used [13], and at 520 nm in alkaline methanol-water solution when using an excitation wavelength of 384 nm [14]. ...
... [35], using the B3LYP/CPCM model and aqueous solvent, the λ ab of 358 nm, and λ em of 454 nm for the enol form and of 670 nm for the keto O5 form of the L molecule were found. In calculations carried out in Ref. [13], the B3LYP-D3/PCM method and methanol as a solvent were considered, obtaining the values of 352 nm for λ ab and 417 nm for λ em . ...
Fisetin and Luteolin are important flavonoids produced in plants and known for their antioxidant, anti-inflammatory, neuroprotective, and analgesic properties. They are also good candidates for different types of biosensors. The model used to describe the fluorescence (FL) emission of these flavonoids involves an excited-state intermolecular proton transfer (ESIPT) process that causes a change in the molecule configuration and a corresponding decrease in the emission energy. Due to the different molecular structures of Fisetin and Luteolin, only one possible proton transfer within the molecule is allowed for each of them: transfer of the H3 proton for Fisetin and of the H5 for Luteolin. Here, we compare their calculated emission wavelengths, obtained using TDDFT/M06-2X/6-31++G(d,p), with their FL emission spectra measured on the corresponding powders and solutions and show that the experimental data are consistent with the presence of the ESIPT process. We also compare the emission wavelengths found for Fisetin and Luteolin with those calculated and measured for Quercetin, where, under photoexcitation, the transfers of both H3 and H5 protons are possible. We analyze the difference in the processes associated with the H3 and H5 proton transfers and discuss the reason for the predominance of the H5 proton transfer in Quercetin. Additionally, a new system of notation for flavonoid molecules is developed.
... This enables the calculation of the exact description of the structure, energy, and molecular properties of the compound. Utilizing DFT for excited states, the time-dependent density functional theory (TD-DFT) can obtain the electronic spectra for absorption and study several processes that involve the excited state [17][18][19][20][21][22][23][24]. ...
... Vibrational (frequency) analysis was carried out at the same theoretical level as the geometrical optimizations to confirm the absence of imaginary frequencies. It is essential that the conformation obtained be localized at the minimum energy point with a positive frequency, since negative frequencies show imaginary conformational conditions [24,49]. For the studied compounds, there were no negative frequency implications, showing that the conformational analysis performed using semi-empirical PM6 and DFT methods was adequate and that the conformations were both real and of sufficient quality to advance the study. ...
... These calculations allow us to generate enough data to comprehend the main theoretical electronic states and UV-vis Vibrational (frequency) analysis was carried out at the same theoretical level as the geometrical optimizations to confirm the absence of imaginary frequencies. It is essential that the conformation obtained be localized at the minimum energy point with a positive frequency, since negative frequencies show imaginary conformational conditions [24,49]. For the studied compounds, there were no negative frequency implications, showing that the conformational analysis performed using semi-empirical PM6 and DFT methods was adequate and that the conformations were both real and of sufficient quality to advance the study. ...
As diseases caused by solar radiation have gained great prominence, several methods to prevent them have been developed. Among the most common, the use of sunscreens is customary and accessible. The application of theoretical methods has helped to design new compounds with therapeutic and protective functions. Natural compounds with described photoprotective potential properties (3-O-methylquercetin, gallic acid, aloin, catechin, quercetin, and resveratrol) were selected to perform theoretical studies. Computational methods were applied to predict their absorption spectra, using DFT and TD-DFT methods with functional B3LYP/6−311+g(d,p) basis sets and methanol (IEFPCM) as a solvent. The main electronic transitions of the compounds were evaluated by observing whether the differences in HOMO and LUMO energies that absorb in the UV range are UVA (320–400 nm), UVB (290–320 nm), or UVC (100–290 nm). Experimental validation was carried out for EMC, quercetin, and resveratrol, demonstrating the consistency of the computational method. Results obtained suggest that resveratrol is a candidate for use in sunscreens. The study provided relevant information about the in silico predictive power of natural molecules with the potential for use as photoprotective adjuvants, which may result in fewer time and resource expenditures in the search for photoprotective compounds.
... The quantum-chemical calculations have been carried out not only for the neutral form of the compound but also for its anionic and isomeric forms. In the work, it was also considered that a potential excited state intramolecular proton transfer process (ESIPT) in scutellarein may be present, taking into account that this process is observed in some other flavonoids with similar structure, such as 3-hydroxyflavone [33], 5-hydroxyflavone [34], apigenin [35,36], luteolin [36] and steppogenin [36]. The quantumchemical calculations verify the prediction of ESIPT occurrence in scutellarein. ...
... The quantum-chemical calculations have been carried out not only for the neutral form of the compound but also for its anionic and isomeric forms. In the work, it was also considered that a potential excited state intramolecular proton transfer process (ESIPT) in scutellarein may be present, taking into account that this process is observed in some other flavonoids with similar structure, such as 3-hydroxyflavone [33], 5-hydroxyflavone [34], apigenin [35,36], luteolin [36] and steppogenin [36]. The quantumchemical calculations verify the prediction of ESIPT occurrence in scutellarein. ...
... The quantum-chemical calculations have been carried out not only for the neutral form of the compound but also for its anionic and isomeric forms. In the work, it was also considered that a potential excited state intramolecular proton transfer process (ESIPT) in scutellarein may be present, taking into account that this process is observed in some other flavonoids with similar structure, such as 3-hydroxyflavone [33], 5-hydroxyflavone [34], apigenin [35,36], luteolin [36] and steppogenin [36]. The quantumchemical calculations verify the prediction of ESIPT occurrence in scutellarein. ...
In this work, the spectroscopic properties of scutellarein (6-hydroxyapigenin) were studied in three organic solvents (methanol, acetonitrile and N,N-dimethylformamide) taking into account possible ionization and isomerization (tautomerization) processes. Significant visible colour changes were reported in the case of scutellarein in N,N-dimethylformamide. It was shown that isomerization processes can be one of the reasons for the observed changes in absorption spectrum, because some scutellarein isomers have an absorption band at about 623 nm while other forms of scutellarein show no absorption in this region. Moreover, spectroscopic properties were studied for cases of scutellarein in acetonitrile and methanol. The molar extinction coefficient has been found in the case of methanol solution which could be used to determine scutellarein concentration in this solvent using spectroscopic methods in future studies.
The quantum-chemical calculations were performed for neutral and anionic forms and for two types of possible isomers of scutellarein in each solvent. The results help explain the experimentally observed rising absorption in the 500-750 nm wavelength range. Another important result of the quantum-chemical calculations is a prediction of excited state intramolecular proton transfer (ESIPT) in scutellarein. This result has been obtained for free molecule in vacuum and in the cases of methanol, acetonitrile and N,N-dimethylformamide solution. It was found that the excited state energy of the normal molecular form is higher than the excited state energy of the tautomer form of scutellarein.
... Zhong, Y et al. reported that IHB promotes ESIPT in the S 0 and S 1 states of flavonoids [188]. Furthermore, Feixiang et al. found that the site where ESIPT occurs, is partly determined by IHB [189]. ...
Despite several decades of research, the beneficial effect of flavonoids on health is still enigmatic. Here, we focus on the antioxidant effect of flavonoids, which is elementary to their biological activity. A relatively new strategy for obtaining a more accurate understanding of this effect is to leverage computational chemistry. This review systematically presents various computational chemistry indicators employed over the past five years to investigate the antioxidant activity of flavonoids. We categorize these strategies into five aspects: electronic structure analysis, thermodynamic analysis, kinetic analysis, interaction analysis, and bioavailability analysis. The principles, characteristics, and limitations of these methods are discussed, along with current trends.
... In addition to serving as a theoretical foundation for the creation of new sunscreen compounds, it is a process in sunscreen processes (Fig. 16a). 49 The main environmental element that contributes to erythema, inammation, photoaging, and skin carcinogenesis is exposure to UV radiation. Vicenin-2 (30) is a bioavonoid that has been identied from a number of therapeutic plants. ...
Sunscreen formulations have undergone significant advancements in recent years, with a focus on improving UV radiation protection, photostability, and environmental sustainability. Chromophore compounds and nanoparticles have emerged as key components in these developments. This review highlights the latest research and innovations in chromophore compounds and nanoparticle-based sunscreens. It discusses the role of nanoparticles, such as zinc oxide and titanium dioxide, in scattering and absorbing UV radiation while remaining cosmetically acceptable. Chromophore compounds, encapsulated in nanoparticles, are explored for their potential to enhance UV protection by absorbing specific wavelengths of light. Additionally, advances in photo-stability, broad-spectrum protection, antioxidant inclusion, and biodegradability are discussed. The evolving landscape of sunscreen technology aims to provide more effective and environment-friendly solutions for safeguarding skin from the sun's harmful effects.
... Using natural active ingredients is becoming the focus of a great deal of interest, especially in the pharmaceutical field [1]. Formulations based on natural products, such as plants, and marine organisms, are good candidates for photoprotective formulations [2][3][4]. However, even showing in most cases low toxicity, natural compounds can present disadvantages, such as low solubility, stability, and absorption. ...
... The dual fluorescence and large Stokes shift in salicylic acid was observed by Weller and his co-worker in 1955 [1], and the ESIPT mechanism has been proposed by J. Goodman in 1978 [2]. Researchers have begun to explore the ESIPT process in detail experimentally and theoretically and have uncovered its application in various areas, such as fluorescent probe [3][4][5], bioimaging [6][7][8], sunscreen [9][10][11], and optical materials [12][13][14]. ESIPT reaction occurs between proton donor and acceptor, forming the intramolecular hydrogen bond. ...
1′-hydroxy-2′-acetonaphthone (HAN) is a useful fluorescence probe based on excited state intramolecular proton transfer (ESIPT). A number of experiments had explored the fluorescence properties of HAN in different microenvironments and applied HAN to bioimaging. However, the mechanism of fluorescence properties of HAN in different microenvironments was not been fully reported. Thus, our research aims to investigate the proton transfer (PT) and fluorescence characteristics of HAN in different microenvironments, focusing on revealing the hydrogen bond dynamics in high-polar aqueous solution (HAN-H2O) and low-polar hydrophobic pocket of bovine serum albumin by the density functional theory (DFT) and time-dependent density functional theory (TD-DFT). Explicit water molecules were placed around HAN to simulate the hydrogen bond interactions between HAN and the water molecules in an aqueous solution. The intermolecular hydrogen bonds slightly affect the geometric structures of HAN, but would inhibit the ESIPT process while increasing the charge transfer distance, leading to red shift of fluorescence. Upon photoexcitation, the intramolecular hydrogen bond had been strengthened, providing the driving force of PT, which resulted in HAN and HAN-H2O undergoing ultrafast ESIPT process. Meanwhile, after photoexcitation, the intermolecular hydrogen bonds were significantly enhanced, decreasing the energy of HAN-H2O in the excited state and promoted the radiationless deactivation of HAN-H2O. Therefore, HAN has weak fluorescence in the aqueous solution.
... 19 Moreover, the plant flavonoid compounds with ESIPT properties have been synthesized and investigated to provide a theoretical basis for sunscreen cosmetics. 20 Research on the properties of sunscreen still needs to be deeply explored. ...
Two novel compounds (HQS and HQSe) with excited-state intramolecular proton transfer (ESIPT) properties were designed based on the compound 2-(2-hydroxy-3-ethoxyphenyl)-3H-quinazolin-4-one (HQ). The parameters related to the ESIPT properties and electronic spectra of HQ and its derivatives were calculated using density functional theory and time-dependent density functional theory methods. The obtained geometric configurations, infrared vibrational spectra, and reduced density gradient scatter plots have shown that the intramolecular hydrogen bond O1···H1-N1 has been weakened upon photoexcitation. Moreover, from the scanned potential energy curves, it can be found that the ESIPT processes of the three compounds have no energy barriers. It is noteworthy that HQS and HQSe can strongly absorb light in the UVA region (∼340 nm) and exhibit weak fluorescence emission in the visible light region, which comes from the keto configuration. The special optical properties of HQS and HQSe can promote their application as potential sunscreen agents.
... Some benzoxazole like 2-(2 ′ -hydroxyphenyl)benzoxazole have absorption bands in the region between 300 and 360 nm and, under excitation with ultraviolet light, emit fluorescence between 500 and 600 nm through a photoinduced excited state intramolecular proton transfer (ESIPT). Compounds that exhibit an ESIPT mechanism are capable of absorbing high energy UV radiation and fast dissipate the harmful UV energy due to an intramolecular rearrangement that occurs in the excited state and are very promising as sunscreen compounds (Ignasiak et al., 2015;Ji et al., 2021). Three 2-(2 ′ -hydroxyphenyl)benzoxazole derivative (Fig. 1): 2-(4 ′ -amino-2 ′ -hydroxyphenyl)benzoxazole (4 ′ -oxol) (1), 2-(5 ′ -amino-2 ′ -hydroxyphenyl)benzoxazole (5 ′ -oxol) (2), and N-[3-(1,3-benzoxazol-2-yl)-4-hydroxyphenyl]acetamide (5 ′ -acetylated-oxol) (3) have shown a wide range of appropriate photophysical properties for the development of new sunscreen products, absorbing both UVA and UVB radiations, with λ max ranging between 336 nm and 364 nm and Sun Protection Factor (SPF) values around 39 . ...
Sunscreening chemicals protect against damage caused by sunlight most absorbing UVA or UVB radiations. In this sense, 2-(2′-hydroxyphenyl)benzoxazole derivatives with amino substituents in the 4′ and 5′ positions have an outstandingly high Sun Protection Factor and adequate photostability, but their toxicity is not yet known. This study aimed to evaluate the toxicity of three synthetic 2-(2′-hydroxyphenyl)benzoxazole derivatives for their possible application as sunscreens. In silico tools were used in order to assess potential risks regarding mutagenic, carcinogenic, and skin sensitizing potential. Bioassays were performed in L929 cells to assess cytotoxicity in MTT assay and genotoxic activities in the Comet assay and micronucleus test. Also, the Salmonella/microsome assay was performed to evaluate gene mutations. The in silico predictions indicate a low risk of mutagenicity and carcinogenicity of the compounds while the skin sensitizing potential was low or inconclusive. The 2-(4′-amino-2′-hydroxyphenyl)benzoxazol compound was the most cytotoxic and genotoxic among the compounds evaluated in L929 cells, but none induced mutations in the Salmonella/microsome assay. The amino substituted at the 4′ position of the phenyl ring appears to have greater toxicological risks than substituents at the 5′ position of 2-(phenyl)benzoxazole. The findings warrant further studies of these compounds in cosmetic formulations.
Fisetin attracts intense attention not only due to its antioxidant and anticancer properties but also because of wide applications in fluorescence probes and sensors, which are based on the dual fluorescence induced by excited-state proton transfer (ESPT). However, to date, its ESPT dynamics remains unknown yet. In this study, we give a comprehensive investigation on ESPT dynamics of fisetin in both protic methanol and aprotic acetonitrile by using femtosecond transient absorption spectroscopy combined with timedependent density functional theory calculations. In acetonitrile, the ESPT time constant of fisetin is 1.2 ps. In methanol, two distinct intermolecular hydrogen bonding configurations contribute to a fast (< 90 fs) and slow ESPT (11.1 ps), respectively. The slow ESPT in methanol explains the higher emission intensity of normal species than in acetonitrile. The excited-state relaxation of fisetin involves two main vibrational modes: rotation between B and C rings and butterfly-like motion of C ring. Our results give insight into the effect of solvent-solute hydrogen bonding interaction on the dual fluorescence, providing a fundamental guide-line for the development of fluorescent probes and sensors based on ESPT.
The photophysics of tris(salicylidenealdimines) (TSALs) has been examined, as they offer the possibility of populating multiple emissive species through the excited-state intramolecular proton transfer (ESIPT) reaction, resulting in broad visible spectrum coverage, a desirable property for white organic light-emitting diodes (wOLEDs). In this contribution, the synthesis and photophysical characterization of a new TSAL derivative, C16, are reported. It displays a distinct emission profile compared to previously studied tris(salicylideneanilines), with an inversion of the ESIPT/LE emission intensity ratio, exhibiting almost exclusively tautomer emission upon excitation in less polar solvents. Ab initio calculations suggest that the absence of emission from the locally excited (LE) state in nonpolar solvents may be related to the competition between two processes: ESIPT and N-pyramidalization of the enaminic nitrogen. Conversely, in polar aprotic solvents, the planar LE conformation is stabilized, and dual emission is observed. In protic solvents, however, the ESIPT reaction is suppressed due to competition with intermolecular hydrogen bonding interactions.
The excited-state proton transfer (ESIPT) behavior of organic fluorophores has attracted much attention due to their unique photophysical properties. So far, ESIPT studies have mainly focused on the transfer of hydrogen atoms between N-N, N-O, or O-O. In this work, a brand-new type of ESIPT molecule based on sulfoxide/sulfenic acid tautomerism has been thoroughly investigated. The sulfoxide/sulfenic acid tautomerization process requires one step and two steps in the ground and first excited singlet states, respectively. A range of density functional theory and time-dependent density functional theory methods have been employed to investigate these structures, and the changes in aromaticity may be responsible for obtaining the ESIPT process. This work presents a novel ESIPT process, showcasing molecules that exhibit distinctive properties compared to conventional ESIPT compounds. These findings are expected to expand the horizons of experimental research in ESIPT.
In this work, we investigated the potential UV protection mechanism of the natural compounds hydroxy resveratrol and pterostilbene by combining theoretical calculations and femtosecond transient absorption spectra (FTAS). The UV absorption spectra showed that the two compounds exhibited strong absorption properties and high photostability. We found two molecules will reach the S1 state or an even higher excited state after UV exposure and molecules in S1 will cross a lower energy barrier to reach the conical intersection. The adiabatic trans-cis isomerization process happened and finally return to the ground. Meanwhile, FTAS clarified the time scale of trans-cis isomerization of two molecules was ∼ 10 ps, which also met the requirement of fast energy relaxation. This work also provides theoretical guidance for developing new sunscreen molecules from natural stilbene.
Flavonoids play diverse roles in plants, comprise a non-negligible fraction of net primary photosynthetic production, and impart beneficial effects in human health from a plant-based diet. Absorption spectroscopy is an essential tool for quantitation of flavonoids isolated from complex plant extracts. The absorption spectra of flavonoids typically consist of two major bands, band I (300-380 nm) and band II (240-295 nm), where the former engenders a yellow color; in some flavonoids the absorption tails to 400-450 nm. The absorption spectra of 177 flavonoids and analogues of natural or synthetic origin have been assembled, including molar absorption coefficients (109 from the literature, 68 measured here). The spectral data are in digital form and can be viewed and accessed at http://www.photochemcad.com. The database enables comparison of the absorption spectral features of 12 distinct types of flavonoids including flavan-3-ols (e.g., catechin, epigallocatechin), flavanones (e.g., hesperidin, naringin), 3-hydroxyflavanones (e.g., taxifolin, silybin), isoflavones (e.g., daidzein, genistein), flavones (e.g., diosmin, luteolin), and flavonols (e.g., fisetin, myricetin). The structural features that give rise to shifts in wavelength and intensity are delineated. The availability of digital absorption spectra for diverse flavonoids facilitates analysis and quantitation of these valuable plant secondary metabolites. Four examples are provided of calculations─multicomponent analysis, solar ultraviolet photoprotection, sun protection factor (SPF), and Förster resonance energy transfer (FRET)─for which the spectra and accompanying molar absorption coefficients are sine qua non.
The photoprotection mechanisms of three chalcones (EDDP, EDPO, and EDHP) in the gas phase and glycerol solvent were investigated using density functional theory and quantum mechanics/molecular mechanics methods. The optimized structures confirmed that the intramolecular hydrogen bonds of the three molecules were enhanced in the S1 state, which favored their proton transfer process. According to the scanned potential energy curves in the S1 state, the three molecules can spontaneously undergo proton transfer in the gas phase, and stable keto configurations do not exist in the glycerol solvent due to their unbridgeable energy barriers. Moreover, the absorption spectra of the three molecules covered the entire ultraviolet region, and their fluorescence spectra spread over the visible and infrared regions. Notably, the oscillator strengths of the maximum absorption peaks were far higher than those of the fluorescence peaks, which meets the requirements of sunscreens for molecular photophysical properties. Furthermore, the geometric structure twisting of the three molecules in glycerol solvent consumed part of the energy from ultraviolet light, causing their fluorescence peak strengths to be faint. The interaction force between glycerol solvent and the three molecules was augmented in the S1 state, explaining why their geometric structure twisted in glycerol solvent. In addition, the three molecules passed our toxicity test, and their free radical scavenging activities were upgraded upon photoexcitation. This property is favorable for promoting their after-sun repair abilities. This work will be expected to deepen the understanding of the sunscreen mechanisms of chalcones.
Flavonoids have been proposed to be natural sunscreens that can provide protection against UV-induced damage in plant. In this study, excited state dynamics of luteolin and quercetin, two natural flavonoids with very low fluorescence quantum yields, were studied by combination of femtosecond transient absorption spectroscopy and quantum chemical calculations. We provide the first experimental demonstration of ultrafast ESIPT process in these two non-emissive flavonoids and proposed that rotation between B- and C-ring after ESIPT is the key to the ultrafast non-radiation decay channels in these two molecules, suggesting that they may indeed behave as natural sunscreens.
Investigating the effects of surrounding microenvironments and substituents on the excited‐state proton transfer (ESPT) mechanism have always been a great challenge, especially in protic solvents and solid state. In this work, a detailed theoretical study on ESPT processes of salicylic acid (SA) and its two derivatives (5ASA and 5NSA) in gas, cyclohexane, acetonitrile, ethanol (EtOH), and crystal phases is performed based on the density functional theory (DFT) and time‐dependent DFT as well as the combined quantum mechanics/molecular mechanics (QM/MM) methods. Intramolecular charge transfer‐induced aggregation‐caused quenching phenomenon of 5ASA is unveiled utilizing the hole–electron analysis. Independent gradient model analysis is implemented to reveal the spontaneous forward proton transfer (PT) behavior of 5ASA. Besides, potential energy surfaces are constructed to evaluate the dominant PT pathway in EtOH, and the related transition state structures are also obtained to accurately provide the intra‐ and inter‐PT energy barriers. Eventually, excited‐state ab initio molecular dynamics computation reaffirms that the intra‐PT reaction is predominant for SA. This theoretical work comprehensively explores the ESPT mechanism and luminescent properties of SA and its two derivatives, which provides a reference for developing efficient organic light‐emitting materials based on ESPT chromophores.
In this present work, four novel molecules (BPN, BPNS, BPS, and BPSN), possessing excited-state intramolecular proton transfer (ESIPT) characteristics, were designed to quantify the impacts of substituent effects on their photophysical properties. By exploring the primary geometrical parameters concerning hydrogen bonds, it should be noticed that the intramolecular hydrogen bonds (IHBs) of the studied molecules have been strengthened at S1 state. Infrared vibrational spectra analysis illustrates that adding electron-donating group thiophene to the proton donor side can weaken the IHBs in comparison to the electron-withdrawing group pyridine. Through investigating the absorption and fluorescence spectra, it can be clearly found that the maximum absorption peaks of the studied molecules are all located in the UVA region, and their regions of fluorescence peaks are harmless to human skin. Furthermore, considering the light intensity factor, it can be concluded that BPNS is the most potential to be used as UV absorbers in the studied molecules. This work investigates the effects of the positions and types of substituent groups on photophysical properties of 2-(2'-hydroxyphenyl) benzazoles derivatives, which can help design and exploit novel UV absorbers.
The substituent and solvent effects on the antioxidant activity of 2'-hydroxychalcone (2'Cha) were systematically explored in gas and three solvent phases by designing six novel compounds (2'Cha-3'NH2, 2'Cha-4'NH2, 2'Cha-5'NH2, 2'Cha-3'CN, 2'Cha-4'CN, and 2'Cha-5'CN) based on the density functional theory (DFT) approach. Significant parameters involved in three primary antioxidant mechanisms, namely the hydrogen atom transfer (HAT), single electron transfer followed by proton transfer (SET-PT), and sequential proton loss electron transfer (SPLET) were computed to confirm the thermodynamically preferred reaction pathway in different media. Besides, 4'-hydroxychalcone (4'Cha) was introduced to unveil the intramolecular hydrogen bond (IHB) effect on the radical scavenging capacity of 2'Cha utilizing the DFT and 2,2-Diphenyl-1-picrylhydrazyl (DPPH) ultraviolet-visible (UV-Vis) spectroscopic methods. Energy barriers and kinetic parameters for HAT reaction of 2'Cha and 4'Cha with hydroperoxyl (HOO•) radical were calculated to further compare the radical-trapping process. The photophysical properties of 2'Cha in benzene, chlorobenzene and ethanol are in good agreement with the measured experimental data and the excited-state antiradical capacity improving mechanism was also confirmed experimentally. The current work not only provides valuable guidance for synthesizing high-efficiency antioxidants but also exploits the potential application fields for 2'Cha.
A fluorescent probe Pi with the excited-state intramolecular proton transfer (ESIPT) properties was synthesized and used to detect the phosgene in solution and gas phases. However, the detection mechanism of the fluorescent probe needs to be further studied. Herein, the density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods were adopted to explore the molecular structures and electronic spectra properties of probe and its product Pio after reacting with phosgene. Through analysis for molecular structure parameters and infrared vibrations accompanied with the hydrogen bond of Pi, it is confirmed that the intramolecular hydrogen bond of Pi is enhanced under light excitation, which illustrates the occurrence of ESIPT reaction combined with the scanned potential energy curves. It can be seen from the simulated spectra that Pi shows double fluorescence through ESIPT process, while the fluorescent product Pio exhibits the single fluorescence due to the disappearance of intramolecular hydrogen bond. Through the study on the structure and optical properties of Pi and Pio, it can be helpful to deeply understand the intrinsic mechanism of the detection of phosgene by the Pi molecule probe, which also supplies a reference to the further study about the fluorescence probe.
In this work, the process of the Excited State Intramolecular Proton Transfer (ESIPT) competition of Kaempferol and Quercetin in methanol was studied by means of the Density Functional Theory (DFT) and the Time-Dependent Density Functional Theory (TDDFT) method. Two different ESIPT reaction pathways were analyzed by the variation trend of the 3D potential energy surfaces (PESs) with the change of the intramolecular hydroxyl bond length through the PESs of the two molecules of the ground state (S0) and the first excited (S1) state. The ESIPT process only occurred between O25–H28 and O22–H28 and was completed within 33.1fs by molecular excited state dynamics simulation. It is demonstrated that when there are two kinds of hydrogen bonds in the molecule, the ESIPT prefers the six-membered ring hydrogen bonds to the five-membered ring hydrogen bonds.
The excited-state intramolecular proton transfer (ESIPT) process is sometimes non-fluorescent owing to interference from other non-radiative processes. Thus, effectively lighting up the “invisible” ESIPT state is crucial. In this work, quinoline–pyrazole (QP) derivatives containing fused and non-fused aromatic frameworks (QP1, QP2, and QP3) were used as model compounds to explore the effects of hydrogen bond (HB) distance and orientation on ESIPT. Analysis of the electronic structures and HB interactions revealed that the HB in fused six-membered ring QP2 was significantly enhanced upon photoexcitation, which making the ESIPT process occur more readily. In contrast, the ESIPT process was less favorable for the more flexible non-fused six-membered ring in QP3 owing to HB weakening in the S1 state. Furthermore, analysis of the potential energy curves indicated that the ESIPT fluorescence of QP1 and QP3 was quenched by intersystem crossing. Remarkably, the dark ESIPT state was successfully illuminated in QP2. Our findings demonstrate that targeted modifications to the molecular structure in the region of HBs can serve as a control knob to effectively regulate the ESIPT fluorescence, providing a route toward potential photoelectric applications.
Recently we have developed a multi-layer energy-based fragment (MLEBF) method to describe excited states of large systems in which photochemically active and inert regions are separately treated with multi-configurational and single-reference electronic structure method and their mutual polarization effects are naturally described within many-body expansion framework. This MLEBF method has been demonstrated to provide highly accurate energies and gradients. In this work, we have further derived the MLEBF method with which highly accurate excited-state hessian matrices of large systems are efficiently constructed. Moreover, in combination with recently proposed embedded atom neutral network (EANN) model we have developed a machine learning (ML) accelerated MLEBF method (i.e. ML-MLEBF) in which photochemically inert region is entirely replaced with trained ML models. ML-MLEBF is found to improve computational efficiency of hessian matrices in particular for large systems. Furthermore, both MLEBF and ML-MLEBF methods are highly parallel and exhibit low-scaling computational cost with multiple CPUs. The present developments could motivate combining various ML techniques with fragment-based electronic structure methods to explore hessian matrix based excited-state properties of large systems.
This work reports this first synthesis of 1D orthomorphic NH4PbI3 perovskite nanocrystals (NCs) considering the role of inorganic ammonium ions at the nanoscale. The addition of bromide ions at the halogen site did not improve the photoluminescence properties. Furthermore, the 3D cubic phase of (NH4)0.5Cs0.5Pb(I0.5Br0.5)3 NCs with bright photoluminescence was synthesized by adding Cs ions into the crystal lattice of (NH4)Pb(I0.5Br0.5)3. Moreover, the photophysical properties of different phase structures were studied using femtosecond transient absorption (FTA) spectroscopy. The ultrafast trap state capture process is a key factor in the change of photoluminescence properties and the cubic phase may be the best structure for photoluminescence. These results suggest that the ammonium ion perovskite (AIP) nanocrystals could be potential materials for optoelectronic applications through A‐site cation substitution.
The unusual large bathochromic shift from a novel near-infrared (NIR)-emitting molecule, 2-[3-(benzo[d]thiazol-2-yl)-2-hydroxy-5-methylstyr-yl]-3-ehtylbenzo[d]thiazol-3-ium iodide (named cyanine 1) with combination of intramolecular charge transfer (ICT) and intramolecular proton transfer (IPT) process in one molecular framework, is systematically investigated using ultrafast transient absorption (TA) spectroscopy and quantum chemical calculations. In order to understand the synergetic coupling effect of the excited state intramolecular proton/charge transfers (ESIPT/ESICT) for the intense near-infrared emission of cyanine 1, an analogue non-ESIPT molecule, 2-[5-(benzo[d]thiazol-2-yl)-2-hydroxystyryl]-3-ehtylbenzo[d]thiazol-3-ium iodide (named cyanine 2) has also been investigated as comparison. Steady-state spectra and theoretical calculations suggest that the large Stokes shift and high fluorescence quantum yield in cyanine 1 originate from the ultrafast ESIPT, which leads to the efficient extension of π-conjugation in the molecular backbone in its excited states. Femtosecond transient absorption spectra further confirm above-mentioned conclusion that an extremely fast ESIPT process occurs in cyanine 1 upon excitation, followed by a solvent reorganization process (ca. 1.5 ps). This solvation is obviously slower compared to cyanine 2 (ca. 0.8 ps), indicating the extent of ESICT concerned ESIPT in keto* form of cyanine 1 is slightly weaker than that of ESICT in cyanine 2, where the fast ESIPT plays an important role in extending the efficient π-conjugation in the molecular backbone by adjusting the electronic charge distribution in keto* form. Such an effect can reduce the radiationless transition due to weak solvation process in keto* form, and then promotes the quantum yield of the large red-shifted fluorescence in cyanine 1.
A complete minimum-energy structural search was carried out for the adsorption of C2H2 molecule on the copper nanoclusters with special attention paid to the most favored adsorption sites. At first, DFT functionals were calibrated with different basis sets including LANL2DZ, 6-31+G*, 6-311+G* and cc-pVTZ in order to calculate the geometry and electronic properties of pure and interacting copper nanoclusters [Cun
and Cun
C2H2 (n ≤ 9)]. The accuracy of the DFT calculations was assessed by comparing them with the experimental values as well as MP2 and CCSD(T). The results showed that TPSSTPSS functional of DFT performed better than all other functionals. The accepted basis sets for the pure and interacting copper nanoclusters were LANL2DZ and “LANL2DZ+aug-cc-pVTZ,” respectively. A relationship between the size of the copper nanoclusters and the chemical reactivity was also established. For this purpose, the adiabatic ionization, adiabatic electron affinity, chemical hardness, electronic chemical potential and electrophilicity were evaluated. According to the obtained results, the C2H2 adsorption on the copper nanoclusters was selective in the terminal coordination. Furthermore, the favored adsorption sites were dominated by the local orientation of the relevant frontier orbitals as well as the distribution of the overall electrostatic potential surfaces of the copper nanoclusters.
With the development of nanotechnology and the wide use of iron oxide nanoparticles, it has become necessary to assess the potential adverse biological effects of magnetite. This study investigated the cytotoxicity, genotoxicity and oxidative damage of different concentrations of magnetite (0 to 1000 mg/L) in human whole blood cultures. After supplementation of magnetite, the blood samples were incubated for 72 h. Cell viability was assessed by the 3-(4,5-dimethylthiazol-2-yl) 2,5-diphenyltetrazolium bromide (MTT) and lactate dehydrogenase (LDH) release assays. The total antioxidant capacity (TAC) and total oxidant status (TOS) were determined to evaluate the dose-dependent effects of magnetite on the oxidant/antioxidant balance and to evaluate the potential oxidative injury due to increased oxidative stress. Genotoxicity was estimated by by the sister chromatid exchange (SCE), micronuclei (MN) and chromosome aberration (CA) assays and determination of 8-oxo-2-deoxyguanosine (8-OH-dG) levels. The results of MTT and LDH assays showed that the higher concentrations of magnetite (100, 150, 300, 500 and 1000 mg/L) decreased cell viability. Concentrations of magnetite higher than 10 mg/L increased TOS levels and decreased TAC levels in human blood cells. Increasing concentrations of magnetite caused significant increases in MN, SCE and CA rates and 8-OH-dG levels. The obtained results showed that magnetite exerted dose-dependent effects on oxidative damage, genotoxicity and cytotoxicity in human blood cells.
Abstract Oxazolidinone antibiotics bind to the highly conserved peptidyl transferase center in the ribosome. For developing selective antibiotics a profound understanding of the selectivity determinants is required. We have performed for the first time technically challenging molecular dynamics simulations in combination with MM-PBSA free energy calculations of the oxazolidinones linezolid and radezolid bound to the large ribosomal subunits of the eubacterium Deinococcus radiodurans and the archaeon Haloarcula marismortui. A remarkably good agreement of the computed relative binding free energy with selectivity data available from experiment for linezolid is found. On an atomic level, the analyses reveal an intricate interplay of structural, energetic, and dynamic determinants of the species-selectivity of oxazolidinone antibiotics: A structural decomposition of free energy components identifies influences that originate from first and second shell nucleotides of the binding sites and lead to (opposing) contributions from interaction energies, solvation, and entropic factors. These findings add another layer of complexity to the current knowledge on structure-activity relationships of oxazolidinones binding to the ribosome and suggest that selectivity analyses solely based on structural information and qualitative arguments on interactions may not reach far enough. The computational analyses presented here should be of sufficient accuracy to fill this gap.
The importance of raw material and extraction parameters for obtaining a high content of flavonoids and phenolic acids in
elderflower extracts was investigated. Nine phenolic acids (3-O-, 4-O-, and 5-O-caffeoylquinic acid, 3-O- and 5-O-p-coumaroylquinic acid, 1,5-di-O-, 3,4-di-O-, 3,5-di-O- and 4,5-di-O-caffeoylquinic acid) and six flavonol glycosides (quercetin-3-O-rutinoside, quercetin-3-O-glucoside, kaempferol-3-O-rutinoside, isorhamnetin-3-O-rutinoside, isorhamnetin-3-O-glucoside, and quercetin-3-O-6″-acetylglucoside) were identified and quantified in elderflowers and/or extracts thereof by liquid chromatography-mass
spectrometry (LC-MS) and high-performance liquid chromatography-diode array detection (HPLC-DAD), respectively. The yield
of elderflower extracts depended significantly on processing conditions and raw material properties and the maximum yield
of elderflower extract was obtained by extraction for a maximum of 10days at 4°C using an extraction liquid consisting of
a maximum of 20w/w % sugars and 5% citric acid. The effects of the extraction liquid composition and raw material on the
concentration of phenolic acids and flavonol glycosides in elderflower extracts were determined by factor analysis. Several
elderberry genotypes were found to be useful for processing of elderflower extracts with a relative high concentration of
phenolic acids and flavonol glycosides.
Multiwfn is a multifunctional program for wavefunction analysis. Its main functions are: (1) Calculating and visualizing real space function, such as electrostatic potential and electron localization function at point, in a line, in a plane or in a spatial scope. (2) Population analysis. (3) Bond order analysis. (4) Orbital composition analysis. (5) Plot density-of-states and spectrum. (6) Topology analysis for electron density. Some other useful utilities involved in quantum chemistry studies are also provided. The built-in graph module enables the results of wavefunction analysis to be plotted directly or exported to high-quality graphic file. The program interface is very user-friendly and suitable for both research and teaching purpose. The code of Multiwfn is substantially optimized and parallelized. Its efficiency is demonstrated to be significantly higher than related programs with the same functions. Five practical examples involving a wide variety of systems and analysis methods are given to illustrate the usefulness of Multiwfn. The program is free of charge and open-source. Its precompiled file and source codes are available from http://multiwfn.codeplex.com.
The absorption and metabolism of anthocyanins (ACN) in humans was studied in four elderly women given 12 g elderberry extract (EBX) (720 mg total ACN), and six elderly women given 189 g lowbush blueberry (BB) (690 mg total ACN). The two major ACN in EBX, cyanidin-3-glucoside and cyanidin-3-sambubioside, as well as four metabolites: 1) peonidin 3-glucoside, 2) peonidin 3-sambubioside, 3) peonidin monoglucuronide, and 4) cyanidin-3-glucoside monoglucuronide were identified in urine within 4 h of consumption using HPLC-MS/MS with diode-array detector detection and retention time. Total EBX ACN excretion was 554 +/- 90 microg (mean +/- SD, n = 4) (0.077% of intake/4 h, wt/wt). In 5 of 6 women fed BB, urine samples contained ACN, which were identified as the original forms based upon comparisons to the BB food sample, which contained 24 ACN, 22 of which were identified by HPLC-MS/MS. Reasonable correlations between BB and urine proportions of the different ACN were obtained except for ACN arabinosides. Total urinary excretion during the first 6 h was 23.2 +/- 10.9 microg (mean +/- SD, n = 5) (0.004% of intake/6 h, wt/wt). Plasma ACN levels were below detection limits using 2 mL plasma in women that consumed BB. This study demonstrates for the first time that in vivo methylation of cyanidin to peonidin and glucuronide conjugate formation occurs after people consume ACN and demonstrates the low absorption and excretion of ACN compared with other flavonoids.
The concept of systemic photoprotection by dietary means is gaining momentum. Skin is continuously exposed to ultraviolet (UV) radiation, the major cause of skin disorders such as sunburn, photodamage, and nonmelanoma skin cancer. Most of the erythemal annual UV dose is encountered under nonvacation conditions, when no sunscreen is applied. In the absence of topically added compounds, skin protection depends solely on endogenous defense. Micronutrients can act as UV absorbers, as antioxidants, or can modulate signaling pathways elicited upon UV exposure. UV-induced erythema is a suitable parameter to assess photoprotection. Dietary protection is provided by carotenoids, tocopherols, ascorbate, flavonoids, or n-3 fatty acids, contributing to maintenance resistance as part of lifelong protection.
The molecular structures of 2, 2‘-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), were calculated by using time-dependent density functional theory (TDDFT) model with M062X method with 6-311G (d, p) basis set. In this work, the ABTS were theoretically investigated from the geometric structure, the energy levels of the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO), the energy level gap △EHOMO-LUMO of the molecular ground state, excited stated properties and the electronic absorption spectra of different oxidation states. We studied the energy levels of LUMO and HOMO of ABTS in different oxidation states. Frontier molecular orbital analysis can provide insight into the nature of excited states. ABTS was synthesized from N-ethylamine by total synthesis. Then, we measured the UV-Vis spectra of ABTS before and after being oxidized by K2S2O8. The calculated electronic structures and photochemical properties of different oxidation state of ABTS were in accordance with the experimental result. This work demonstrates the relationship between the electronic structures and photochemistry of different oxidation states ABTS hence paves the way for the rationally synthesis and deepen understanding of the photophysical properties of ABTS materials.
In this work, we proposed the natural molecules chlorogenic acid (CA) and isochlorogenic acid A (ICAA) could be used as sunscreens for the first time. The non-radiative energy relaxation mechanisms of two molecules were presented through a combination of theoretical calculations and spectral experiments. We demonstrated that the trans-cis photoisomerization coordinate in the picosecond timescale could take place in both the natural molecules chlorogenic acid (CA) and isochlorogenic acid A (ICAA). ICAA has a double CA conjugated structure. It has been demonstrated that only one CA conjugated structure in ICAA can be photoexcited. Moreover, the photoisomerization channel of ICAA was similar to CA. We reported a dual conjugated system in a plant-derived sunscreens and the dual conjugated system improves the energy absorption efficiency to some extent. This work confirmed that the plant-derived CA and ICAA could be potential natural sunscreen molecules and created an avenue for designing novel sunscreen compounds.
The density functional theory (DFT) and time-dependent density functional theory (TDDFT) were performed to investigate the ground state and excited state hydrogen-bonding dynamics of flavonoid in hydrogen donating aqueous solution. We demonstrated that the intermolecular hydrogen bond C=O•••H-O between flavonoid and water molecules is significantly strengthened in the electronically excited-state upon photoexcitation of the hydrogen-bonded complex. The radiationless deactivation via intramolecular proton transfer in excited state (ESIPT) can be facilitated by the hydrogen bond strengthening in the excited state. At the same time, quantum yields of the excited-state deactivation via fluorescence are correspondingly decreased. The total fluorescence of flavonoid in polar protic solvents can be drastically quenched by hydrogen bonding. As a consequence, we propose a fluorescence modulation mechanism by hydrogen bonding to explain fluorescence emissions of flavonoid in hydrogen- bonding solvents and no hydrogen-bonding solvents. Given that water molecules have anomalous properties that are different from other small organic molecules that form hydrogen bonds with flavonoids, this theoretical study has reference significance for the development of in vivo probes. Hopefully, the newly proposed mechanism can inspire experimentalists to develop and synthetic non-toxic high signal-to-noise ratios without the need to wash fluorescent probes for individual targets in vivo.
This work demonstrated that tunable photoluminescence of the low-dimensional hybrid halide perovskites via the doping strategy is feasible, and hence paves the way towards the investigation and application of high-performance single photoluminescence perovskite material with broadband white light emission. This work reported the first synthesis of one-dimensional (1D) (C4N2H14)2Pb1-xMnxBr4 perovskite microcrystals (MCs) with tunable broadband white-light emission and long-lived STE (self-trapped exciton) emission. The overall photoluminescence mechanism under the regulation of defect engineering of 1D (C4N2H14)2Pb1-xMnxBr4 MCs was formulated for the first time. Photoluminescence mechanism of these MCs involves competition of FE (free exciton) and STE and ⁴T1 states. This competitive mechanism further promotes photoluminescence tunability ranging from blue-white to white to orange-red for Mn-doped MCs. Moreover, time-resolved emission spectra show the changes of lifetime of these MCs at different emission wavelength. These perovskite MCs have a long-lived STE emission, which indicates that the more effective exciton combinations are occurring in them. For comparation, the Mn-doping strategy can regulate structural defect of these MCs, which promotes or suppresses transitions of FE→STE, FE→⁴T1, STE→FE and further tunes photoluminescence. This work paves the way towards the investigation and development of optoelectronic application of perovskite MCs material.
Organic semiconductors (OSCs) materials are currently under intense investigation because of their potential applications such as organic field-effect transistors, organic photovoltaic devices, and organic light-emitting diodes. Inspired by the selenization strategy can promote anisotropic charge carrier migration, and selenium-containing compounds have been proved to be promising materials as OSCs both for hole and electron transfer. Herein, we now explore the anisotropic transport properties of the series of selenium-containing compounds. For the compound containing SeSe bond, the SeSe bond will break when attaching an electron, thus those compounds cannot act as n-type OSCs. About the different isomer compounds with conjugated structure, the charge transfer will be affected by the stacking of the conjugated structures. The analysis of chemical structure and charge transfer property indicates that Se-containing materials are promising high-performance OSCs and might be used as p-type, n-type, or ambipolar OSCs. Furthermore, the symmetry of the selenium-containing OSCs will affect the type of OSCs. In addition, there is no direct relationship between the R groups with their performance, whether it or not as p-type OSCs or n-types. This work demonstrates the relationship between the optoelectronic function and structure of selenium-containing OSCs materials and hence paves the way to design and improve optoelectronic function of OSCs materials.
In this paper, we use time-dependent density functional theory (TD-DFT) to investigate the effects of protic and aprotic solvents on the excited state intramolecular proton transfer (ESIPT) and hydrogen bond (ESHB) mechanisms of the alizarin. The calculation results show that there are mainly two forms of alizarin: alizarin-A and alizarin-B (both are isomers), in which alizarin-A is more stable than alizarin-B. In the aprotic (dimethylsulfoxide and n-heptane) solvents, alizarin-A is more prone to proton transfer reactions than alizarin-B in the excited state. In protic (methanol) solvent, the ESIPT process of alizarin-A is carried out without energy potential barrier, while the energy potential barrier of alizarin-B is only 0.04 kcal/mol, which is easier to occur than in aprotic solvent conditions. The scatter plot and isosurface of the reduced density gradient function indicate that the ESHB of alizarin in the protic solvent is stronger than the aprotic solvent. In other words, the hydroxyl group at the proton transfer site undergoes more hydrogen bonding interactions in the protic solvent, which will facilitate the occurrence of the ESIPT process. In general, our work will contribute to regulate the ESIPT process of alizarin and its derivatives through solvent effects in the future, as well as application to more fields.
Mehr als nur eine Phase: Mithilfe einer Phasenregulationsstrategie wurden erstmals Perowskit-Nanokristalle von NH4PbI3 und (NH4)0.5Cs0.5Pb(I0.5Br0.5)3 synthetisiert. Letztere Kristalle zeigen eine deutlich erhöhte Photolumineszenz und bessere Stabilität.
Abstract
This work reports this first synthesis of 1D orthomorphic NH4PbI3 perovskite nanocrystals (NCs) considering the role of inorganic ammonium ions at the nanoscale. The addition of bromide ions at the halogen site did not improve the photoluminescence properties. Furthermore, the 3D cubic phase of (NH4)0.5Cs0.5Pb(I0.5Br0.5)3 NCs with bright photoluminescence was synthesized by adding Cs ions into the crystal lattice of (NH4)Pb(I0.5Br0.5)3. Moreover, the photophysical properties of different phase structures were studied using femtosecond transient absorption (FTA) spectroscopy. The ultrafast trap state capture process is a key factor in the change of photoluminescence properties and the cubic phase may be the best structure for photoluminescence. These results suggest that the ammonium ion perovskite (AIP) nanocrystals could be potential materials for optoelectronic applications through A-site cation substitution.
In this work, the intermolecular hydrogen bonding interaction in both the ground state and electronic excited states of the hydrogen bonded compounds Serotonin–(H2O)nn = 1,2 were investigated by the density functional theory (DFT) and the time-dependent density functional theory (TDDFT) method. By monitoring the structures in different electronic states, it has been demonstrated that the hydrogen bonds in Serotonin–(H2O)nn = 1, 2 are strengthened upon excitation. And the hydrogen bond site of 5-OH of the ring is always strengthened, more significantly. The simulated infrared (IR) spectrum demonstrated that the red-shifts of the stretching vibration frequencies of hydrogen bonded OH groups were consistent with the change trend of hydrogen bonds. Furthermore, the interaction among the hydrogen bonds caused by the bridged-water structure should be considered while making analysis of the calculated results such as the structure information and the IR spectrum.
A speed tunable excited-state intramolecular proton transfer (ESIPT)system featuring a seven-membered ring, -NH- type hydrogen bonding pyrrole-indole moiety based on ‘naked’ diazaborepins (NDABs)was exhibited. In this paper, the speed of ESIPT process can be tuned by the substituents on indole ring, including electron donating and withdrawing group for NDAB-H, NDAB-OMe, NDAB-COOEt, NDAB-NEt 2 , NDAB-CF 3. It has explained by DFT and TD-DFT calculation in nonpolar toluene. The energy gaps between N[sbnd]S 1 and T[sbnd]S 1 (△E = E T-S1 − E N-S1 )of most NDABs are slightly positive, except for the energy gap of NDAB-NEt 2 with strong donating group on indole ring is negative. Meanwhile, the S 1 state potential energy curve of NDABs with a small energy barrier is in the order NDAB-NEt 2 < NDAB-OMe ~ NDAB-H < NDAB-COOEt < NDAB-CF 3 . Therefore, it indicates that ESIPT reaction could happen on the NDABs system. Strong withdrawing groups on indole ring of NDABs could restrain the ESIPT process and strong donating groups could promote the ESIPT process, which is in good agreement with the corresponding Stokes shift between absorption and emission spectra in N and/or T tautomer experimentally. The ESIPT process of NDABs in polar aprotic DMSO by the same calculation method also has been certified.
Dental caries, starting from demineralization of enamel and dentine, is closely related with acid-producing bacteria in oral cavity, for example, Streptococcus mutans. Remineralization is an efficient way to prevent the disease progression and facilitate the therapy of incipient caries. Therefore, for the purpose of effective dentine repair, remineralization and antibacterial should be combined simultaneously. However, most of the literatures only focus on one single aspect, while combing remineralization and antibacteria for dentine repair in one system is rarely reported. Here in this work, phosphoryl-terminated poly(amide-amine) dendrimers were loaded with apigenin, a water-nonsoluble drug antibacterial agains Streptococcus mutans. The apigenin-loaded dendrimers bind strongly with dentine, which further induce dentine tubules occlusion through mineralization in artificial saliva, and the release of apigenin can prevent further erosion of dentine by bacteria. Meanwhile, the phosphorylated dendrimers are easily prepared by one-step modification of poly(amide-amine) and exhibit good cytocompatibility. This strategy developed here can provide reference for the design of effective anti-caries materials.
In this present work, adopting density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods, we theoretically research the excited state dynamical process about two imide compound N-cyclohexyl-3-hydroxyphthalimide (3HNHPI) and 3,6-Dihydroxy-N-cyclohexylphthalimide (DHNHPI). We find the intramolecular hydrogen bonds in these two systems should be strengthening in the S1 state, which may trigger excited state intramolecular proton transfer (ESIPT) reaction. Analysis about charge redistribution implies the tendency of ESIPT reaction for both 3HNHPI and DHNHPI. However the constructed potential energy surfaces confirm that the ESIPT process should occur for 3HNHPI rather than DHNHPI molecule, which is consistent with previous experiment [Phys. Chem. Chem. Phys. 17 (2015) 30659–30669]. Via transition state (TS) theory, we successfully account for the vague explanation in previous work and clarify that why the proton transfer reaction missing for DHNHPI in the S1 state.
The excited-state intramolecular charge transfer (ICT) of LD 490 were investigated in different hydrogen-bond-donating solvents (α scale) on the basis of the Kamlet–Taft solvatochromic parameters (π*, α, β). The femtosecond transient absorption spectra and the kinetics decay rate reveal that with an increase of solvent's α capacity, the long-lived picosecond process, which is attributed to the ICT, becomes much faster. Combining with time-dependent density functional theory (TDDFT) calculations, we demonstrate that the enhancement of α acidity substantially increases the electronegativity of the carbonyl oxygen in LD 490, which strengthen excited-state intermolecular hydrogen bonding interactions and consequently facilitate the ICT process.
2, 4-dibenzothiazolyl-phenol (2, 4-DBTP), a fluorophore developing induced emission properties, undergoes excited state intramolecular proton transfer (ESIPT) taking place along its strong hydrogen bond. 2,4-DBTP has been investigated in the polar and nonpolar solvents by means of time-dependent density functional theory (TDDFT). The TDDFT absorption and emission wavelengths obtained through the vertical approximation are in good agreement with their experimental counterparts, confirming the existence of an ESIPT process and indicating that the selected level of theory is reasonable. Hydrogen bond strengthening has been testified in the S1 state based on comparing primary bond lengths and bond angles involved in the intramolecular hydrogen bond between the S0 and S1 state. Furthermore, the frontier molecular orbitals (MOs) analysis method manifest the intramolecular charge transfer, which reveals the tendency of ESIPT process. To further characterize the ESIPT process, we determined the potential-energy curves of the S0 and S1 states.Compared with 2,4-DBTP monomer, the S1 state potential energy curve of 2,4-DBTP-MeOH complex has a bigger slope with no potential barrier. Therefore, we can indicate that the ESIPT process for 2,4-DBTP is much easier in methanol solvent.
Dibenzoylmethane (DBM), a phytochemical agent, occurring as a minor constituent in the root extracts of liquorice has a potential for anti-photoaging effects. It acts as a UVA absorber that filters out and prevents the penetration of UV radiations into various cell components. In this study, DBM loaded o/w microemulsion (ME) was developed and evaluated for anti-photoaging effect in mice. The ME was evaluated for various physicochemical characteristics, stability, ex-vivo skin permeation studies and in vivo evaluation in mice model of UV-radiation induced photodamage. The mean globule size of DBM loaded ME was found to be 35.550 ± 4.879 nm. The mean cumulative amount permeated/area and skin retention of DBM in 24 h from the ME was 6.81 and 5.16 folds higher, respectively as compared to the conventional cream of DBM. In vivo anti-photoaging effect on mice skin was evaluated in terms of visual scoring, pinch test, biochemical estimations and histopathological studies. Results clearly demonstrated the promising efficacy of ME formulation in preventing wrinkles, lesions and other macroscopic and microscopic changes associated with chronic UV exposure. Hence, it can be concluded that DBM ME can be used effectively used as sunscreen agent to protect against the damaging effect of UV rays.
S-adenosylhomocysteine hydrolase (SAHase) is a cellular enzyme that plays a key role in the methylation process, and a potential drug target in the discovery of antiviral and anticancer agents. There is increasing interest in determining its activity in the biological and clinical fields with chemosensors but with limited success so far. Herein, we designed and developed for the first time an off/on-type of fluorogenic substrate (NADE) that is directly responsive to SAHase activity. NADE used 1, 8-naphthalimide as the signal reporter and adenosine (Ade) as the reaction center; removal of the Ade moiety enhanced the fluorescence by >10-fold. Kinetic study showed that NADE followed a non-Michaelis-Menten pattern that corresponded to the allosteric behavior of SAHase. NADE showed excellent selectivity and functioned efficiently in cells, allowing the microscopic imaging of SAHase activity. NADE can also be used to identify and measure the effectiveness of inhibitors in a markedly superior way. In a word, NADE would be broadly useful in clinical applications and academic studies.
In the present work, N,N-dimethylanilino-1,3-diketone (DMADK), a new chromophore of the unsymmetrically substituted 1,3-diketone [R. Ghosh and D. K. Palit, Photochem. Photobiol. Sci. 12 (2013) 987–995], has been investigated about the excited state proton transfer (ESPT) based on the time-dependent density functional theory (TDDFT) method. The experimental UV/Vis and emission spectra are well reproduced by the calculated vertical excitation energies in the S0 and S1 states. For the optimized Enol-B* structure, the twisted intermolecular charge transfer (TICT) process can be confirmed in the S1 state. Hydrogen bond strengthening has been testified in the S1 state based on comparing primary bond lengths and bond angles involved in the intramolecular hydrogen bond between the S0 state and the S1 state. Furthermore, infrared spectra (IR) at the OH stretching vibrational region and Molecular electrostatic potential surface (MEPS) based on our calculation also declare the phenomenon of hydrogen bond strengthening. The frontier molecular orbitals (MOs) analysis, MEPS, Mulliken's charge distribution analysis, Hirshfeld charge distribution analysis and Natural bond orbital (NBO) analysis methods manifest the intramolecular charge transfer, which reveals the tendency of excited state intramolecular proton transfer (ESIPT) process. The constructed PESs of both S0 and S1 states demonstrate that ground state intramolecular proton transfer (GSIPT) as well as reversed GSIPT processes exists in the S0 state, and the ESIPT coupled with the TICT process can occur in the S1 state rather than sequential ESIPT and TICT processes.
Solid state emitters based on excited state intramolecular proton transfer (ESIPT) have been attracting considerable interest since the past few years in the field of optoelectronic devices because of their desirable unique photophysical properties. The photophysical properties of the solid state ESIPT fluorophores determine their possible applicability in functional materials. Less fluorescence quantum efficiencies and short fluorescence lifetime in the solid state are the shortcomings of the existing ESIPT solid state emitters. Designing of ESIPT chromophores with high fluorescence quantum efficiencies and a long fluorescence lifetime in the solid state is a challenging issue because of the unclear mechanism of the solid state emitters in the excited state. Reported design strategies, detailed photophysical properties, and their applications will help in assisting researchers to overcome existing challenges in designing novel solid state ESIPT fluorophores for promising applications. This review highlights recently developed solid state ESIPT emitters with focus on molecular design strategies and their photophysical properties, reported in the last five years.
In the present work, 3, 3', 4', 7-tetrahydroxyflavone (fisetin), as one of the most extensive distributed flavonoids, has been investigated on the excited state proton transfer (ESPT) based on the time-dependent density functional theory (TDDFT) method. The calculated absorption and fluorescence spectra based on the TDDFT method are in agreement with the experimental results. Two kinds of structures of fisetin chromophore are found in the first excited (S1) state, which may be due to the proton transfer reactive. Hydrogen bond strengthening has been testified in the S1 state based on comparing staple bond lengths and bond angles involved in hydrogen bonding between the S0 state and the S1 state. In addition, the calculated infrared spectra at the O-H stretching vibrational region and calculated hydrogen bond energy also declare the phenomenon of hydrogen bond strengthening. The frontier molecular orbitals (MOs) analysis and Natural bond orbital (NBO) manifest the intramolecular charge transfer of fisetin chromophore, which reveals the tendency of proton transfer. The potential energy surfaces of the S0 and S1 states are constructed to explain the mechanism of the proton transfer in excited state in detail.
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Organic glasses containing chromophores with large first hyperpolarizabilities (β) are promising for compact, high-bandwidth, and energy-efficient electro-optic devices. Systematic optimization of device performance requires development of materials with high acentric order and enhanced hyperpolarizability at operating wavelengths. One essential component of the design process is the accurate calculation of optical transition frequencies and hyperpolarizability. These properties can be computed with a wide range of electronic structure methods implemented within commercial and open-source software packages. A wide variety of methods, especially hybrid density-functional theory (DFT) variants have been used for this purpose. However, in order to provide predictions useful to chromophore designers, a method must be able to consistently predict the relative ordering of standard and novel materials. Moreover, it is important to distinguish between the resonant and nonresonant contribution to the hyperpolarizabiliy and be able to estimate the trade-off between improved β and unwanted absorbance (optical loss) at the target device’s operating wavelength.
The competitive mechanism between dissociation and ionization of hydrogen molecular ion in intense fields has been theoretically investigated by using an accurate non-Born-Oppenheimer method. The relative yield of fragments indicates that the dissociation and ionization channels are competitive with the increasing laser intensity from 5.01013 to 2.01014 W/cm2. In the case of intensity lower than 1.01014 W/cm2, the dissociation channel is dominant, with a minor contribution from ionization. The mechanism of dissociation includes the contributions from the bond softening, bond hardening, below-threshold dissociation and above-threshold dissociation, which are strongly dependent on the laser intensity and initial vibrational state. Furthermore, the ionization dominates over the dissociation channel at the highest intensity of 2.01014 W/cm2. The reasonable origin of ionization is ascribed as above-threshold Coulomb explosion, which has been demonstrated by the space-time dependent ionization rate. Moreover, the competition mechanism between dissociation and ionization channels are displayed on the total kinetic energy resolved (KER) spectra, which could be tested at current experimental conditions.
Growth, seed yield and accumulation of ultraviolet (UV)-absorbing compounds were studied in chalcone isomerase-defective tt-5 mutant of Arabidopsis thaliana and its Landsberg erecta (Ler) progenitor under full-spectrum solar radiation and a series of filters which attenuated progressively larger portions of the UV-B and UV-A radiation bands. The purpose was to determine: (1) whether or not the tt-5 mutant could be induced to grow more or less normally, given adequate protection from damaging UV in the presence of high levels of photosynthetic active radiation (PAR) so that it could be used as a surrogate for mechanistic high UV studies; (2) whether the generalized plant action spectrum or the alfalfa DNA damage action spectrum would best describe the observed responses; and (3) if the traditional Mylar (polyester) filter provides an adequate control for UV damage studies. Maximum rosette diameter (MRD), plant height and fresh weight at harvest and seed yield were measured, along with absorbance of leaf extracts at 300 nm and accumulation of total phenolics before and after exposure to UV. Three types of UV filters were used: cellulose diacetate (CD), which non-selectively transmits all the UV reaching the earth's surface; Mylar, which cuts off UV below about 320 nm; and polyvinyl chloride (PVC) which cuts off UV below about 340 nm. Generally, Ler showed no significant growth effects under any of the treatments except for plant height which was reduced in Mylar and CD when compared to PVC. Conversely, tt-5 generally exhibited progressive decreases in all the measures of plant growth with PVC resulting in the best growth, Mylar treatments showing significant reductions and CD treatments even greater reductions. It was clear that even under these circumstances: the disruption to secondary metabolism in tt-5 makes it unsuitable for mechanistic studies of high UV-B damage; the alfalfa DNA action spectrum seemed the best correlated with observed responses and suggests a significant damaging radiation band which is not affected by stratospheric ozone; and since the damaging radiation extends beyond the Mylar cut-in, this material will not provide an adequate control for UV damage studies.
A procedure based on the polarizable continuum model (PCM) has been applied to reproduce solvent effects on electronic spectra in connection with the time-dependent density functional theory (TD-DFT). To account for solute-solvent interactions, a suitable operator has been defined, which depends on the solute electronic density and can be used to modify the TD-DFT equations for the calculation of molecular polarizabilities and of electronic transition energies. The solute-solvent operator has been derived from a PCM approach depending on solute electrostatic potential: Recently, it has been shown that such an approach also provides an excellent treatment of the solute electronic charge lying far from the nuclei, being particularly reliable for this kind of applications. The method has been tested for formaldehyde in water and in diethyl-ether, and then applied to the calculation of solvent effects on the n→π∗ transition of diazabenzenes in different solvents. The computed transition energies are in fairly good agreement with experimental values. © 2001 American Institute of Physics.
An excited-state intramolecular proton transfer (ESIPT) process in 2-(2'-hydroxyphenyl)benzimidazole and -benzoxazole (HPBI and HBO, respectively) has been studied using steady-state and time-resolved emission spectroscopy at various temperatures and by semiempirical quantum chemical methods. For both of them two distinct ground-state rotamers I and II respectively responsible for the ''normal'' and the ''tautomer'' emission have been detected. In hydrocarbon solvents at room temperature and at 77 K the tautomer emission predominates over the normal emission for both HPBI and HBO. This indicates that rotamer II, responsible for the tautomer emission, is intrinsically stabler than rotamer I, which causes the normal emission. In alcoholic glass at 77 K for HPBI a dramatic enhancement of the normal emission is observed. It is suggested that due to the increased solvation, the more polar rotamer I becomes stabler than II for HPBI in alcohol and the substantial temperature variation is due to the change in the population of the two rotamers with temperature. From the detailed temperature variation in alcoholic medium the ground-state energy difference between rotamers I and II is determined. In dioxane-water mixtures it is observed that with the addition of water the quantum yield of the normal emission increases, which is ascribed to the inhibition of the ESIPT process due to the formation of an intermolecular hydrogen bond involving water. CNDO/S-CI calculations were performed optimizing the ground: state geometry by the AM1 method. Details of the energy, dipole moment, and charge distribution of the rotamers in the ground state (S-0) and the first excited singlet state (S-1) and the barrier for the interconversion of I and II in S-0, S-1, and first excited triplet state are discussed. The calculation indicates that the barrier for the interconversion of the two rotamers is too high in the excited state (S-1 and T-1) for free interconversion.
Five flavonoids, kaempferol, apigenin, luteolin, quercetin and tiliroside and two sesquiterpenes lactones, were isolated from Lychnophorapasserina. Tiliroside, found in the genus Lychnophora, can be used for chemical standardization and its presence in high amounts, relative to other flavonoids, may suggest that it is an antioxidant as well as being a UV-protectant.
In this perspective we introduce the basic photophysics of the excited-state intramolecular proton transfer (ESIPT) chromophores, then the state-of-the-art development of the ESIPT chromophores and their applications in chemosensors, biological imaging and white-light emitting materials are summarized. Most of the applications of the ESIPT chromophores are based on the photophysics properties, such as design of fluorescent chemosensors by perturbation of the ESIPT process upon interaction with the analytes, their use as biological fluorescent tags to study DNA-protein interaction by probing the variation of the hydration, or design of white-light emitting materials by employing the large Stokes shift of the ESIPT chromophores (to inhibit the Föster energy transfer of the components). The photophysical mechanism of these applications is discussed. Furthermore, a new research topic concerning the ESIPT chromophores is proposed based on our group's results, that is, to develop organic triplet sensitizers with ESIPT chromophores.
Garlic has been reported in many previous studies as a potent chemopreventive agent. The protective effect of garlic has been ascribed to the presence of organosulphur compounds (OSC). In this study, the efficacy of aged garlic extract (AGE) compared to diallyl disulfide (DADS) in protecting against toxicity induced by cadmium (Cd) in 1321N1 and HEK293 cells was investigated. The involvement of the transcription factor Nrf2 in this protection was also examined. The results show that AGE significantly prevented loss of cell viability in Cd-treated 1321N1 and HEK293 cells. In comparison DADS had no significant effect in protecting HEK293 cells but did protect 1321N1 cells. AGE significantly reduced Cd-induced TBARS production and LDH leakage in the two cell lines, and AGE and DADS both increased GSH levels in Cd-treated cell lines. Pre-treatment of cells with AGE or DADS increased expression of the protective enzyme NAD(P)H:quinone oxidoreductase (NQO1), and this was associated with the accumulation of the transcription factor Nrf2. These results show that AGE and DADS have beneficial effects against Cd-induced toxicity, and this protection appears to be mediated via induction of cytoprotective enzymes in an Nrf2-dependent manner. This indicates the potential for using AGE as a chemoprevention strategy for Cd toxicity.
Recently, organic fluorescent molecules harnessing the excited-state intramolecular proton transfer (ESIPT) process are drawing great attention due to their unique photophysical properties which facilitate novel optoelectronic applications. After a brief introduction to the ESIPT process and related photo-physical properties, molecular design strategies towards tailored emission are discussed in relation to their theoretical aspects. Subsequently, recent studies on advanced ESIPT molecules and their optoelectronic applications are surveyed, particularly focusing on chemical sensors, fluorescence imaging, proton transfer lasers, and organic light-emitting diodes (OLEDs).
Multiple exposures to solar ultraviolet (UV) radiation cause critical damage to skin that may lead to the development of several cutaneous disorders including skin cancer. Protection against sun-induced damage is therefore a highly desirable goal. Chemoprevention via plant-based agents may be a useful approach for the prevention? of UV-induced neoplasia. In this study, we assessed (1) whether baicalin protected against multiple UVB exposure-mediated damage in skin of C57BL/6 mice and (2) the underlying mechanisms. C57BL/6 mice were topically pretreated with baicalin (1 mg/cm(2) skin area/mouse/100 μL acetone) and were exposed to UVB 30 min later (180 mJ/cm(2), on alternate days × 10 exposures). The animals were sacrificed 24 h after the last UVB exposure. Skin edema, histopathology changes, Ki-67, PCNA, and COX-2 were assessed to determine UVB induced damage. Multiple exposures of C57BL/6 mice to UVB resulted in an increase in skin edema and hyperplasia. Topical application of baicalin prior to UVB radiation resulted in a significant inhibition of Ki-67, PCNA and COX-2 expression. These protective effects of baicalin may also inhibit UVB-induced skin carcinogenesis. Based on this data, we suggest that baicalin could be developed as an agent for the management of conditions elicited by multiple UV exposures, including skin cancer.
Ultraviolet (UV) radiation induces DNA damage, oxidative stress, and inflammatory processes in human keratinocytes resulting in skin inflammation, photoaging, and photocarcinogenesis. The flavonoid luteolin is one of the most potent antioxidative plant polyphenols. We investigated the UV protective and antioxidant properties of luteolin in human keratinocytes in vitro, ex vivo, and in vivo. Spectrophotometric measurements revealed extinction maxima of luteolin in the UVB and UVA range. UV transmission below 370 nm was <10%. In human skin, luteolin effectively reduced the formation of UVB-induced cyclobutane pyrimidine dimers. The free radical scavenging activity of luteolin was assessed in various cell-free and cell-based assays. In the cell-free DPPH assay the half-maximal effective concentration (EC₅₀) of luteolin (12 μg/ml) was comparable to those of Trolox (25 μg/ml) and N-acetylcysteine (32 μg/ml). In contrast, in the H₂DCFDA assay performed with UVB-irradiated keratinocytes, luteolin (EC₅₀ 3 μg/ml) was much more effective compared to Trolox (EC₅₀ 12 μg/ml) and N-acetylcysteine (EC₅₀ 847 μg/ml). Luteolin also inhibited both UVB-induced skin erythema and the upregulation of cyclooxygenase-2 and prostaglandin E₂ production in human skin via interference with the MAPK pathway. These data suggest that luteolin may protect human skin from UVB-induced damage by a combination of UV-absorbing, DNA-protective, antioxidant, and anti-inflammatory properties.
The absorption and emission properties of the two components of the yellow color extracted from weld (Reseda luteola L.), apigenin and luteolin, have been extensively investigated by means of DFT and TDDFT calculations. Our calculations reproduce the absorption spectra of both flavonoids in good agreement with the experimental data and allow us to assign the transitions giving rise to the main spectral features. For apigenin, we have also computed the electronic spectrum of the monodeprotonated species, providing a rationale for the red-shift of the experimental spectrum with increasing pH. The fluorescence emission of both apigenin and luteolin has then been investigated. Excited-state TDDFT geometry optimizations have highlighted an excited-state intramolecular proton transfer (ESIPT) from the 5-hydroxyl to the 4-carbonyl oxygen of the substituted benzopyrone moiety. By computing the potential energy curves at the ground and excited states as a function of an approximate proton transfer coordinate for apigenin, we have been able to trace an ESIPT pathway and thus explain the double emission observed experimentally.
Time-dependent density functional theory method was performed to investigate the intramolecular and intermolecular hydrogen bonding in both the singlet and triplet electronic excited states of aminofluorenones AF, MAF, and DMAF in alcoholic solutions as well as their important roles on the excited-state photophysical processes of these aminofluorenones, such as internal conversion, intersystem crossing (ISC), twisted intramolecular charge transfer (TICT), and so forth. The intramolecular hydrogen bond C=O...H-N can be formed between the carbonyl group and amino group for the isolated AF and MAF. However, no intramolecular hydrogen bond for DMAF can be formed. At the same time, the most stable conformation of DMAF is out-of-plane structure, where the two dihedral angles formed between dimethyl groups and fluorenone plane are 163.1 degrees and 41.74 degrees, respectively. The formation of intramolecular hydrogen bond for AF and MAF is tightly associated with the intersystem crossing of these aminofluorenones. Furthermore, the ISC process can be dominantly determined by the change of intramolecular hydrogen bond between S(1) and T(1) states of aminofluorenones. Since the change of hydrogen bond between S(1) and T(1) states of AF is stronger than that of MAF, the rate of ISC process for AF is faster than that for MAF. Moreover, the rate constant of the ISC process of DMAF is nearly close to zero because of the absence of intramolecular hydrogen bond. On the other hand, the intermolecular hydrogen bond C=O...H-O can be also formed between all aminofluorenones and alcoholic solvents. The internal conversion process from S(1) to S(0) state of these aminofluorenones is facilitated by the intermolecular hydrogen bond strengthening in the electronic excited state of aminofluorenones because of the decrease of energy gap between S(1) and S(0) states. At the same time, the change of intermolecular hydrogen bond between S(1) and T(1) states for AF is much stronger than that for MAF, which may also contribute to the faster ISC process for AF than that for MAF in the same solvents. The TICT process plays an important role in the deactivation of the photoexcited DMAF, since the TICT process along the twisted dihedral angle is nearly barrierless in the S(1) state of DMAF. However, the TICT cannot take place for AF and MAF because of the presence of the intramolecular hydrogen bond.
A correlation-energy formula due to Colle and Salvetti [Theor. Chim. Acta 37, 329 (1975)], in which the correlation energy density is expressed in terms of the electron density and a Laplacian of the second-order Hartree-Fock density matrix, is restated as a formula involving the density and local kinetic-energy density. On insertion of gradient expansions for the local kinetic-energy density, density-functional formulas for the correlation energy and correlation potential are then obtained. Through numerical calculations on a number of atoms, positive ions, and molecules, of both open- and closed-shell type, it is demonstrated that these formulas, like the original Colle-Salvetti formulas, give correlation energies within a few percent.
We report the effects of protonation on the structural and spectroscopic properties of 1,4-dimethoxy-2,5-bis(2-pyridyl)benzene (9) and the related AB coploymer poly{2,5-pyridylene-co-1,4-[2,5-bis(2-ethylhexyloxy)]phenylene} (7). X-ray crystallographic analysis of 9, 1,4-dimethoxy-2,5-bis(2-pyridyl)benzene bis(formic acid) complex 10, and 1,4-dimethoxy-2,5-bis(2-pyridinium)benzene bis(tetrafluoroborate salt) (11) establishes that reaction of formic acid with 9 does not form an ionic pyridinium salt in the solid state, rather, the product 10 is a molecular complex with strong hydrogen bonds between each nitrogen atom and the hydroxyl hydrogen in formic acid. In contrast, reaction of 9 with tetrafluoroboric acid leads to the dication salt 11 with significant intramolecular hydrogen bonding (N−H···O−Me) causing planarization of the molecule. The pyridinium and benzene rings in 11 form a dihedral angle of only 3.9° (cf. pyridine−benzene dihedral angles of 35.4° and 31.4° in 9, and 43.8° in 10). Accordingly, there are large red shifts in the optical absorption and emission spectra of 11, compared to 9 and 10. Polymer 7 displays a similar red shift in its absorption and photoluminescence spectra upon treatment with strong acids in neutral solution (e.g. methanesulfonic acid, camphorsulfonic acid, and hydrochloric acid). This is also observed in films of polymer 7 doped with strong acids. Excitation profiles show that emission arises from both protonated and nonprotonated sites in the polymer backbone. The protonation of the pyridine rings in polymer 7, accompanied by intramolecular hydrogen bonding to the oxygen of the adjacent solubilizing alkoxy substituent, provides a novel mechanism for driving the polymer into a near-planar conformation, thereby extending the π-conjugation, and tuning the absorption and emission profiles. The electroluminescence of a device of configuration ITO/PEDOT/polymer 7/Ca/Al is similarly red-shifted by protonation of the polymer.
The adoption of the 7th amendment of the European Cosmetic Directive 76/768/EEC requires any cosmetic product containing any of 26 raw materials identified by the Scientific Committee on Cosmetic Products and Non-Food Products intended for Consumers as likely to cause a contact allergy when present above certain trigger levels to be declared on the package label. Of these 26, 24 are volatile and can be analyzed by GC. This paper describes a method for the quantitative analysis of these volatile raw materials in perfume ingredients as well as complex perfume compositions. The method uses sequential dual-column GC-MS analysis. The full-scan data acquired minimize the false-positive and false-negative identifications that can be observed with alternate methods based on data acquired in the SIM mode. For each sample, allergen levels are determined on both columns sequentially, leading to two numerical results for each allergen. Quantification limits for each allergen in a perfume mixture based on the analysis of a standard are <4 mg/kg. This is well below the level that would trigger label declaration on the consumer good. Calibration curves for all allergens are linear (r > 0.999) and stable for multiple days. Studies on perfumes spiked with multiple allergens at 30, 50, and 70 mg/kg show recoveries close to nominal values.
The concept of photoprotection by dietary means is gaining momentum. Plant constituents such as carotenoids and flavonoids are involved in protection against excess light in plants and contribute to the prevention of UV damage in humans. As micronutrients, they are ingested with the diet and are distributed into light-exposed tissues, such as skin or the eye where they provide systemic photoprotection. beta-Carotene and lycopene prevent UV-induced erythema formation. Likewise, dietary flavanols exhibit photoprotection. After about 10-12 weeks of dietary intervention, a decrease in the sensitivity toward UV-induced erythema was observed in volunteers. Dietary micronutrients may contribute to life-long protection against harmful UV radiation.
The time-dependent density functional theory (TDDFT) method was carried out to investigate the hydrogen-bonded intramolecular charge-transfer (ICT) excited state of 4-dimethylaminobenzonitrile (DMABN) in methanol (MeOH) solvent. We demonstrated that the intermolecular hydrogen bond C[triple bond]N...H-O formed between DMABN and MeOH can induce the C[triple bond]N stretching mode shift to the blue in both the ground state and the twisted intramolecular charge-transfer (TICT) state of DMABN. Therefore, the two components at 2091 and 2109 cm(-1) observed in the time-resolved infrared (TRIR) absorption spectra of DMABN in MeOH solvent were reassigned in this work. The hydrogen-bonded TICT state should correspond to the blue-side component at 2109 cm(-1), whereas not the red-side component at 2091 cm(-1) designated in the previous study. It was also demonstrated that the intermolecular hydrogen bond C[triple bond]N...H-O is significantly strengthened in the TICT state. The intermolecular hydrogen bond strengthening in the TICT state can facilitate the deactivation of the excited state via internal conversion (IC), and thus account for the fluorescence quenching of DMABN in protic solvents. Furthermore, the dynamic equilibrium of these electronically excited states is explained by the hydrogen bond strengthening in the TICT state.
A detailed quantum chemical study on five peptides (WG, WGG, FGG, GGF and GFA) containing the residues phenylalanyl (F), glycyl (G), tryptophyl (W) and alanyl (A) -- where F and W are of aromatic character -- is presented. When investigating isolated small peptides, the dispersion interaction is the dominant attractive force in the peptide backbone-aromatic side chain intramolecular interaction. Consequently, an accurate theoretical study of these systems requires the use of a methodology covering properly the London dispersion forces. For this reason we have assessed the performance of the MP2, SCS-MP2, MP3, TPSS-D, PBE-D, M06-2X, BH&H, TPSS, B3LYP, tight-binding DFT-D methods and ff99 empirical force field compared to CCSD(T)/complete basis set (CBS) limit benchmark data. All the DFT techniques with a '-D' symbol have been augmented by empirical dispersion energy while the M06-2X functional was parameterized to cover the London dispersion energy. For the systems here studied we have concluded that the use of the ff99 force field is not recommended mainly due to problems concerning the assignment of reliable atomic charges. Tight-binding DFT-D is efficient as a screening tool providing reliable geometries. Among the DFT functionals, the M06-2X and TPSS-D show the best performance what is explained by the fact that both procedures cover the dispersion energy. The B3LYP and TPSS functionals-not covering this energy-fail systematically. Both, electronic energies and geometries obtained by means of the wave-function theory methods compare satisfactorily with the CCSD(T)/CBS benchmark data.