Enol Form Research Articles

Determination of the structure of a new potentially active pharmaceutical substance

Introduction. The development of methods for analyzing new potentially active pharmaceutical substances is an important part of substance standardization. An integrated approach to confirming the structure of a substance is especially important when the substance may exist in different tautomeric forms, since the properties of the substance may change depending on tautomerism, affecting, among other things, the pharmacological activity.Aim. The aim of our study was to determine the tautomeric composition of the potential active pharmaceutical substance 5-butyl-6-hydroxy-2,3-diphenylpyrimidin-4(3H)-one in solid state and solution for the subsequent development of its dosage form and determination of bioavailability.Material and methods. The object of the study was the substance 5-butyl-6-hydroxy-2,3-diphenylpyrimidin-4(3H)-one. Spectra were taken to confirm the structure: infrared on a PerkinElmer Spectrum 3 device (PerkinElmer Inc., USA) in the frequency range from 4000 to 400 cm–1, nuclear magnetic resonance 1H and 13C on a pulsed broadband spectrometer Bruker AM-500 (400 and 100 MHz) (Bruker, Germany) in DMSO-d6 solvent, ultraviolet using SF-2000 (LLC "OKB Spektr", Russia) in the wavelength range of 250–400 nm, and high-performance liquid chromatography with tandem mass spectrometry (HPLC-MS/MS) was also carried out.Results and discussion. A feature of pyrimidine hydroxy derivatives is the presence of tautomeric forms, which can affect both the physicochemical properties of the substance and its pharmacological activity. The study found that in the solid state, 5-butyl-6-hydroxy-2,3-diphenylpyrimidin-4(3H)-one is in equilibrium between the diketo form and the enol form, and when the substance is dissolved in dimethyl sulfoxide (DMSO), the enol form is predominant. The purity was confirmed by HPLC-MS/MS.Conclusion. The structure of 5-butyl-6-hydroxy-2,3-diphenylpyrimidin-4(3H)-one was confirmed by IR and NMR spectroscopy. UV spectra were obtained, and HPLC-MS/MS was performed to exclude possible absorption of ultraviolet radiation by impurities.

Theoretical study of solvent effects on the white light emission mechanism of single molecule 4-OH-naphthalimide

Organic white light materials fabricated on the basis of single molecules have applied to manufacture the white light-emitting diodes due to their good photostability and relatively simple material preparation. In this work, the different fluorescence emission mechanisms of the NapH1 in n,n-dimethylformamide (DMF) and toluene are investigated to elucidate the process for generating single-molecule near-white-light. From the analysis of bond lengths and electrostatic potential analysis, the intermolecular hydrogen bond can form in DMF instead of in toluene. From the potential energy curves, it is clear that intermolecular proton transfer is not feasible in either DMF or toluene. Frontier molecular orbitals analysis, the dissociation constants and the vertical excitation energies are used to confirm that NapH1 can undergo the deprotonation process in DMF rather than in toluene. Combined with the calculations of the fluorescence values, only the original structure exists stably in toluene which emits blue fluorescence. And the dual fluorescence peaks of NapH1 in DMF are originated from the enol form and the deprotonated form, interacting jointly to emit near-white light. This work contributes to the investigation and advancement for single-molecule organic white luminescent materials.

Acetylacetone – 2-methoxyethanol solutions: Fourier transform infrared spectral studies

The H-bond interactions in the solutions of acetylacetone (AcAc) with 2-methoxyethanol (2-MOE) have been investigated using FTIR spectroscopy. Theoretical calculations on monomers (eight enol isomers and one keto form) and dimers of AcAc have been carried out. The results confirm that both the keto and enol forms of AcAc exist as monomers in liquid AcAc. The analysis of the carbonyl and hydroxyl bands indicates the existence of both the AcAc conformers in the solutions. The intensity of the bands due to the hydroxyl stretching and in-plane bending vibrations decreases rapidly with a decrease in 2-MOE concentration.

The Use of the Carbonyl Group (C-3) of Isatin for the Construction of Pyrazoline Moiety and the Study of its Antioxidant Activity

A series of novel pyrazoline derivatives 5-13 were synthesized in three steps from isatin, with yields ranging from 40 to 72% over the multistep procedure. The first step included the condensation of isatin with p-aminoacetophenone to afford the corresponding Schiff base 1 in a 75% yield. In the second step, the enolate form of Schiff base 1 was reacted with different aromatic aldehydes (benzaldehyde, p-nitrobenzaldehyde, and p-chlorobenzaldehyde) to give the title chalcone derivatives 2-4 in 60-72 yields. In the third step, pyrazoline derivatives 5-13 were synthesized via cycloaddition reactions between compounds 2-4 and hydrazine hydrate, phenyl hydrazine, or p-nitrophenyl hydrazine. The cycloaddition produced the target pyrazoline compounds in 40-72% isolated yields. All prepared compounds were characterized by FT-IR and 1H NMR spectroscopy. Some of the prepared compounds were tested for antioxidant properties.

Copper Incorporated Covalent Organic Framework as a Heterogeneous Catalyst for CuAAC Reaction

AbstractCovalent organic frameworks (COFs) incorporating metal are attractive alternatives for metal‐catalyzed organic transformations. For effective metal incorporation in COF a favorable ligand environment is required. Pyridine and hydrazone units can provide effective binding sites for transition metals. The major challenge in synthesizing hydrazone‐linked COFs is the inherent flexibility of the linker, causing differences in lengths and orientations during solvothermal synthesis. We demonstrate that incorporation of enol form in the framework facilitates non‐covalent interactions such as hydrogen bonding, reduces degrees of freedom and enhances rigidity. Here, we synthesized TFP‐PyHz COF utilizing 2,4,6‐trihydroxybenzene‐1,3,5‐tricarbaldehyde (TFP) and pyridine‐2,6‐dicarbohydrazide. Enol form in the framework was confirmed by comparing the IR and 13C solid‐state NMR spectra of TFP‐PyHz with its model compound. The presence of this enol form also facilitates the incorporation of Cu2+ through post‐modification as confirmed by IR and XPS analysis of postmodified Cu‐TFP‐PyHz. The copper‐incorporated material Cu‐TFP‐PyHz is utilized as a heterogeneous catalyst for copper‐catalyzed click reactions, enabling the synthesis of 1,4‐triazoles.

Effects of functional groups on ESIPT and antioxidant activity of apigenin: A non-existent enol* state fluorescein

The development and enhancement of antioxidant drugs, which are aimed at mitigating DNA damage, mutations, and cancer, are of paramount significance in the biomedical sphere. In recent years, antioxidant drug molecules with photoluminescence have sprung up like mushrooms. Apigenin (AP), characterized by its distinctive property of excited state intramolecular proton transfer (ESIPT), plays a pivotal role in mediating antioxidant and anticancer activities. Despite being a representative molecule of the non-existent enol form (E*) state with ESIPT nature, there is a notable lack of theoretical investigations into its antioxidant properties. Herein, density functional theory (DFT) and time-dependent DFT methodologies were utilized to explore the effects of various functional groups on AP molecules in a methanol solvent. Studies have demonstrated that for the non-existent E* state fluorescence molecule AP, the ESIPT process can significantly enhance the antioxidant potency of AP and its derivatives. However, the introduction of electron-withdrawing groups significantly accelerated the ESIPT process while simultaneously suppressing the antioxidant activity of AP-CN. Conversely, the incorporation of electron-donating groups effectively inhibited the ESIPT process, yet markedly enhanced the antioxidant activity of AP-NH2. This investigation furnishes vital perspectives and sources of reference for the conception and advancement of groundbreaking antioxidant medications that aim to tackle non-existent E* state molecules.

Pyrimidine derivative mimicking the locked enol form of avobenzone acts as a photostable UVAII and UVB filter

The broad UVA (UVAI and UVAII) filtering activity of the sunscreen agent avobenzone is due to its enolic forms which undergoes ketonization followed by degradation upon exposure to sunlight/radiation. The current report aims to lock the enolic forms of avobenzone through chemical derivatization that preserves the chelated intramolecular hydrogen bond geometry. The pyrimidine derivative mimicking both the enol-1 and enol-2 forms of avobenzone has been synthesized and evaluated for it photostability under natural sunlight by UV spectroscopy. The avobenzone pyrimidine derivative acts as a broad-spectrum UVAII, and UVB filter and exhibits unprecedented photostability under sunlight. The new derivative of avobenzone is a valuable additive to the tool kit of chemical UV filters and its poor skin permeability relative to the native avobenzone may be an advantage for cosmetics.

Effect of Reactive Oxygen Species Photoproduced in Different Water Matrices on the Photostability of Gadusolate and Mycosporine-Serinol.

In the past few years, there has been an increasing interest in mycosporines-UV-absorbing molecules-bringing important insights into their intrinsic properties as natural sunscreens. Herein, mycosporine-serinol and gadusol (enolate form)/gadusolate were exposed to UV radiation via a solar simulator and the photostability was assessed in pure water and different natural matrices like river, estuary and ocean water. In general, this study revealed that the photodegradation of gadusolate and mycosporine-serinol was higher in natural matrices than in pure water due to the generation of singlet oxygen on UV irradiation. In pure water, in terms of photostability, both gadusolate and mycosporine-serinol were found to offer good protection and high performance in terms of photodegradation quantum yield ((0.8 ± 0.2) × 10-4 and (1.1 ± 0.6) × 10-4, respectively). Nonetheless, the photostability of mycosporine-serinol was found to be superior to that of gadusolate in natural water, namely, ocean, estuary and river. The present work highlights how mycosporine-serinol and gadusolate resist photodegradation, and supports their role as effective and stable UV-B sunscreens.

Photoexcitation Dynamics of 4-Aminopthalimide in Solution Investigated Using Femtosecond Time-Resolved Infrared Spectroscopy

Excited-state intramolecular proton transfer (ESIPT) reactions are crucial in photoresponsive materials and fluorescent markers. The fluorescent compound 4-aminophthalimide (4-AP) has been reported to exhibit solvent-assisted ESIPT in protic solvents, such as methanol, wherein the solvent interacts with 4-AP to form a six-membered hydrogen-bonded ring that is strengthened upon excitation. Although the controversial observation of ESIPT in 4-AP has been extensively studied, the molecular mechanism has yet to be fully explored. In this study, femtosecond infrared spectroscopy was used to investigate the dynamics of 4-AP in methanol and acetonitrile after excitation at 350 and 300 nm, which promoted 4-AP to the S1 and S2 states, respectively. The excited 4-AP in the S1 state relaxed to the ground state, while 4-AP in the S2 state relaxed via the S1 state without the occurrence of ESIPT. The enol form of 4-AP (Enol 4-AP) in the S1 state was calculated to be ~10 kcal/mol higher in energy than the keto form in the S1 state, indicating that keto-to-enol tautomerization was endergonic, ultimately resulting in no observable ESIPT for 4-AP in the S1 state. Upon the excitation of 4-AP to the S2 state, the transition to Enol-4-AP in the S1 state was found to be exergonic; however, ESIPT must compete with an internal conversion from the S2 to the S1 state. The internal S2 → S1 conversion was significantly faster than the solvent-assisted ESIPT, resulting in a negligible ESIPT for the 4-AP excited to the S2 state. The detailed excitation dynamics of 4-AP clearly reveal the molecular mechanism underlying its negligible ESIPT, despite the fact that it forms a favorable structure for solvent-assisted ESIPT.

An interesting aggregation induced red shifted emissive and ESIPT active hydroxycoumarin tagged symmetrical azine: Colorimetric and fluorescent turn on–off–on response towards Cu2+ and Cysteine, real sample analysis and logic gate application

We report a newly synthesized 7-diethylamino-4-hydroxycoumarin tagged symmetrical azine derivative (SHC), with an interesting color transformation from yellowish green to orange via aggregation induced red shifted emissive (117 nm) feature in THF-H2O mixture. Interestingly, the single crystal X-ray analysis of this molecule demonstrates that two hydroxycoumarin moieties were present in azine unit, among them one of the coumarin units was exist as enol form and another one transferred to keto form via ground state proton transfer reaction. The optical responses of the compound in different solvents exposed the observation of dual emissive bands which corresponds to the presence of ESIPT phenomenon in SHC molecule. Further, this characteristic was confirmed by absorption, emission, solid state structure and time resolved fluorescence decay measurements. Furthermore, the fluorophore, SHC was exploited as a colorimetric and turn on–off–on fluorescent probe for detection of Cu2+ ions and Cysteine (Cys). The 1:1 binding ratio of the probe with Cu2+ and Cys with SHC-Cu2+, was established via Job plot analysis, mass spectral technique and the DFT calculations. The probe, SHC was employed for the detection of copper ions in the environmental real water samples. Finally, the reversible fluorescent turn on–off–on character of the probe, SHC was established to construct the IMPLICATION logic gate application.

Divergent Metabolic Fates of Aromatic Amino Acid-Derived Isomers: Insights from Ex Vivo Metabolomics and HDX-HRMS/MS-Based Resolution of Tautomers.

Tautomers are one of the many types of isomers, and differences in tautomeric structures confer altered chemical and biological properties. Using ultrahigh-performance liquid chromatography-high-resolution mass spectrometry (UHPLC-HRMS) ex vivo metabolomics, we investigate, in whole blood, the divergent metabolism of enol and keto forms of indole-3-pyruvate (IPyA), a tautomeric product of aromatic amino acid metabolism. Two new compounds resulting from IPyA metabolism were discovered, 3-(1H-indol-3-yl)-2,3-dioxopropanoic acid or "indole-3-oxopyruvic acid" and glutathionyl-indole pyruvate (GSHIPyA), which were characterized via ultraviolet photodissociation (UVPD) and higher-energy collisional dissociation (HCD). Computational calculations support the hypothesis that GSHIPyA forms specifically through the enol form of IPyA. GSHIPyA is also hypothesized to be tautomeric, and a hydrogen-deuterium exchange-high-resolution tandem mass spectrometry (HDX-HRMS/MS) approach is developed to prove the presence of an enol and keto tautomer. HDX of GSHIPyA labels the keto form with an additional deuterium, relative to the enol form. HRMS/MS of the labeled isomers is employed to leverage the relationship of resolving power scaling inversely with the square root of m/z, for Orbitrap mass analyzers. HRMS/MS yields a smaller-molecular-weight deuterated tautomeric product ion, reducing the analyte ion m/z and thus lowering the resolving power necessary to separate the deuterated keto tautomer product ion from the [13]C product ion.

α-Functionalization of the Carbonyl Group for the Construction of Pyrazoline Rings Derived from 1,3-Indandione

This work includes the synthesis of new pyrazoline derivatives 5-13 over three steps starting from 1,3-indandione. The first step included the acylation of 1,3- indandione with acetyl chloride to produce compound 1 with excellent yield (90%). In the second step, the enolate form of 1 was condensed with various aromatic aldehydes (benzaldehyde, p-nitrobenzaldehyde, and p chlorobenzaldehyde) to afford the corresponding α,β-unsaturated carbonyl derivatives 2-4 in high yields (93-95%). The third step involved a reaction of 2-4 with hydrazine hydrate, phenyl hydrazine, and p-nitrophenyl hydrazine to give the desired pyrazoline derivatives 5-13 in yields ranging from 70 to 83%. The structure of the synthesized compounds was verified through FT-IR and 1H NMR spectroscopy. Additionally, a subset of the synthesized compounds underwent testing to evaluate their antibacterial and antioxidantproperties.

Tautomer-Selective Fluorescence Spectroscopy of Oxyluciferin Anions.

Bioluminescence in fireflies and related insects arises as emission from the fluorophore oxyluciferin, yet the color of the emission in these insects can range from red to green. The chromophore's microenvironment or multiple tautomeric forms may be responsible for the color tuning; however, these effects are difficult to separate in condensed phases. To investigate the role of oxyluciferin tautomerization in the color tuning mechanism, gas-phase spectroscopy eliminates solvent effects and allows us to study the fluorescence from individual tautomers. Using a home-built mass-spectrometry setup with a cylindrical ion trap cooled with liquid nitrogen, we measure fluorescence from the enol-locked form of oxyluciferin in the gas phase and characterize the photophysics of both keto and enol forms. At 100 K, the enol-locked form has an emission maximum of 564 ± 1 nm, coinciding with a previously reported assignment in oxyluciferin. We measure the absorption spectrum and find a maximum at 560.5 ± 0.5 nm, which implies a Stokes shift of 110 cm-1. The absorption spectrum is compared to Franck-Condon simulated spectra that identify one dominant vibrational mode in the transition. Additionally, we ultimately separated the emission by the enol and keto forms present in the trap by selectively exciting each form. We demonstrate that fluorescence measured close to the 0-0 transition limits the reheating of the ions, thereby providing the coldest ions and therefore the narrowest emission spectra. These experimental data are also crucial benchmarks for computational studies, offering actual emission spectra in the gas phase for both tautomeric forms. Thus, our findings serve as essential reference points for excited-state calculations aimed at understanding the color tuning mechanism of bioluminescence computationally.

Photochemical coupling reaction of phenacyl benzoate with acetone to form 1,4‐dicarbonyl compound enabled by charge transfer

AbstractPhotolysis of phenacyl benzoates tethered with a phenol or anisole in acetone resulted in the formation of 1,4‐dicarbonyl compounds, coupling products of the phenacyl moiety with acetone. The reaction occurs via electron and/or proton transfer from a triplet exciplex, leading to the formation of a phenacyl radical, which then adds to the enol form of acetone. The reaction also occurs in intermolecular fashion with external electron donors.

Profoxydim in Focus: A Structural Examination of Herbicide Behavior in Gas and Aqueous Phases.

This study investigates the chemical structure of profoxydim, focusing on its E-isomer, the main commercial form. The research aimed to determine the predominant tautomeric forms under various environmental conditions. Using proton and carbon-13 NMR spectroscopy alongside theoretical modeling, we examined tautomers and their conformers in different solvents (MeOD, DMSO, CDCl3, benzene) to mimic gas and aqueous phases. The findings reveal that the enolic form dominates in the gas phase, while the ketonic form prevails in aqueous environments, providing key insights into the herbicide's environmental behavior. We also observed an isomeric transition from E to Z under acidic conditions, which could affect profoxydim's reactivity in natural environments. The theoretical calculations indicated that in acidic conditions, the E and Z forms are nearly degenerate, with the E form remaining dominant in neutral environments. Additionally, QSAR models assessed the toxicity of various tautomers, revealing significant differences that could impact bioactivity and environmental fate. This research offers crucial insights into the structural dynamics of profoxydim, contributing to cyclohexanedione chemistry and the development of more effective herbicides.

Synthesis, characterization, DFT and molecular docking study of an antiviral drug, the crystallized 6-methoxylated derivative of favipiravir, in the presence of an iron (III) Lewis acid.

Few years ago, the COVID-19 infection, caused by SARS-CoV-2 virus, presented a worldwide health pandemic that taken the life of millions of people. In this concern, Favipiravir (FAV) has attracted considerable attention as an effective antiviral drug against this disease. In this study, the favipiravir's derivative (3‑hydroxy-6-methoxypyrazine-2-carboxamide) was synthetized, in presence of iron (III), and fully characterized through various analytical techniques including single-XRay, IR, UV and 1H/13C NMR. The refinement show the exclusive existence of enol form in the solid state. In solution, UV and NMR data were used to highlight the tautomeric equilibrium of this molecule. Additionally, the density functional theory (DFT) calculations were achieved to estimate the chemical parameters, electronic affinity and molecular electrostatic potential of the compound. Mulliken atomic charges as well as the chemical reactivity descriptors were investigated. Finally, the two tautomer forms of synthetized derivative were docked on SARS-CoV-2 main protease (PDB: 6LU7) and spike receptor-binding domain (PDB: 7BZ5) to evaluate their binding affinity. The docking simulation studies was predicted that the two forms had high binding affinity the critical amino acids residues of the receptor. This affinity was attributed to the presence of several hydrogen bonds for both tautomer along with five different hydrophobic interactions with the enol form. These results conduct to conclude that the synthetized product could be an interest potential drug for that type of diseases.

Novel Brønsted Acid Catalyzed C-C Bond Activation and α-Alkylation of Ketones.

A novel approach for the α-alkylation of ketones was developed using Brønsted acid-catalyzed C-C bond cleavage. Both aromatic and aliphatic ketones reacted smoothly with 2-substituted 1,3-diphenylpropane-1,3-diones to afford α-alkylation products with high yields and with excellent regioselectivity, in which the 1,3-dicarbonyl group acted as a leaving group in the presence of the catalyst TfOH. Mechanism experiments showed that the β-C-C bond cleavage of diketone and the shift of the equilibrium towards the enol formation from ketone are driving forces that induce the desired products.

Synthesis of 5-(4-Formylphenyl)barbituric Acid to Access Enolizable Chromophoric Barbituric Acids

AbstractBarbituric acids mono-substituted at the 5-position show keto–enol tautomerism. In the keto form, conjugation to an aryl substituent is interrupted due to the sp³-hybridized carbon atom at the 5-position of barbituric acid. The enol form generates a conjugated π-system to the aryl substituent and acts as an electron-donating group. If the aryl substituent is electron-deficient, a push-pull system is generated that shows typical UV/Vis absorption. These types of compounds are difficult to access synthetically due to their intrinsic convertibility. The synthesis of barbituric acids with a 4-formylphenyl functionality at the 5-position is reported. This compound, 5-(4-formylphenyl)barbituric acid, could be used to introduce extended π-systems with electron-withdrawing groups in great variety by simple condensation reactions. We demonstrate this by a Horner–Wadsworth–Emmons reaction that forms the enolizable dye (E)-5-(4-(4-nitrostyryl)phenyl)barbituric acid.

Emissively enhanced novel azo compounds featuring with ESIPT core

This study presents the synthesis and detailed characterization of novel azo compounds featuring Excited State Intramolecular Proton Transfer (ESIPT) cores derived from orcinol, resorcinol, and 2-naphthol. Using a comprehensive suite of spectroscopic techniques, including Nuclear Magnetic Resonance (NMR), Liquid Chromatography-Mass Spectrometry (LC-MS), Ultraviolet-Visible (UV–Vis) spectroscopy, and fluorescence spectroscopy, we explored the unique photophysical properties of these compounds. Notably, the synthesized compounds exhibited exceptionally large Stokes shifts, with values recorded at 204 nm, 251 nm, and 168 nm for compounds 1A, 2A, and 3A, respectively. These shifts indicate significant potential for applications in areas such as optical sensing and fluorescent imaging. Furthermore, Density Functional Theory (DFT) calculations were employed to investigate the nonlinear optical (NLO) properties of the enol and keto tautomeric forms of these compounds. The findings revealed that compound 2A, in particular, demonstrated impressive first-order hyperpolarizability, especially in chloroform, underscoring its suitability for advanced nonlinear optical applications. The study highlights the pivotal role of the ESIPT mechanism, where efficient intramolecular hydrogen bonding facilitates proton transfer upon excitation, leading to enhanced fluorescence properties. This phenomenon is particularly pronounced in compound 2A, where dual O—H interactions contribute to its remarkable fluorescence behavior, making it a standout candidate for use in high-performance optical materials. These findings not only advance our understanding of azo compounds and their versatile photophysical characteristics but also open new avenues for their application in cutting-edge technologies such as optical sensors, imaging agents, laser materials, and other fluorescence-based devices. By strategically leveraging the ESIPT process and the unique structural features of these compounds, this research paves the way for future innovations in the field of advanced optical materials and photonic devices.

External electric field induced emission behavior for ESIPT-based 2-(benzo[d]thiazol-2-yl)-4-(pyren-1-yl)phenol towards near-infrared region

Organic light-emitting diodes (OLEDs) for low energy transfer and double emission, but the current methods for regulating ESIPT processes are mostly solvent and substituent effects. Here, utilizing the density theory functional (DFT) and time-dependent density functional theory (TD-DFT) methods, the ESIPT process controlled by an external electric field (EEF) is proposed, and the changes in photophysical properties of 2-(benzo[d]thiazol-2-yl)-4-(pyren-1-yl)phenol (PyHBT) are investigated. Structural parameter variations and IR vibrational spectra measure the prerequisite for the ESIPT process, namely, intramolecular hydrogen bond (IHB) strength, and the scanned potential energy curves (PECs) demonstrate that the ESIPT process of PyHBT is harder to execute as the positive EEF increases, and the opposite is true for the negative EEF. The absorption and fluorescence spectra show shifts under the distinct EEFs, and even the emission wavelength reaches the short-wave near-infrared (SW-NIR) region (780–1100 nm), such as 815.2 nm for a positive EEF of + 30 × 10-4 a.u. in the keto form. Additionally, the fluorescence intensity of PyHBT is strongly influenced by the positive EEF, especially in the enol form, and the investigation of the mechanism by hole-electron analysis demonstrates that under the positive EEF, the twisted intramolecular charge transfer (TICT) process is induced, which triggers the weakening of the fluorescence intensity. In summary, our work not only complements the theoretical approach to modulate the ESIPT process, but also reveals that the photophysical properties of materials affected by the external electric field are even expected to reach the NIR region.