Azo Form Research Articles

Activation of H2O2-HCO3- by Ca2Co2O5 for pollutant degradation.

The bicarbonate-activated hydrogen peroxide (BAP) system is widely studied for organic pollutant degradation in wastewater treatment. Ca2Co2O5, a heterogeneous catalyst containing multivalent cobalt including Co(II) and Co(III), was herein investigated as a BAP activator, and Acid Orange 7 (AO7) was used as a model pollutant. Ca2Co2O5 exhibited good activation performance. The degradation rate and the initial rate constant of the Ca2Co2O5-activated BAP system were 5.4 and 11.2 times as high as the BAP system, respectively. The removal rate of AO7 reached 90.9% in 30min under optimal conditions (AO7 20mg/L, Ca2Co2O5 0.2g/L, H2O2 1mM, NaHCO3 5mM, pH 8.5, 25℃). The Ca2Co2O5 catalyst exhibited good stability and recyclability, retaining 85% of AO7 removal rate in the fifth run. Compared to the BAP system, a lower dosage of H2O2 was required and a higher initial concentration of pollutants allowed for effective degradation in the Ca2Co2O5-BAP system. X-ray photoelectron spectroscopy was used to analyze the catalytic mechanism. The analysis showed that the good catalytic performance of Ca2Co2O5 attributes to its high proportion of oxygen vacancies and Co(III) species, and the presence of Ca. The active species O2•-, •OH, and 1O2 are responsible for the degradation, as indicated by the quenching experiments. The degradation mechanism of AO7 was speculated based on UV-Vis spectral analysis and the identification of degradation intermediates. The azo form, naphthalene and benzoic rings in the AO7 structure are destroyed in the decomposition. This research provides a feasible approach to designing effective and reusable BAP activators for pollutant degradation in wastewater treatment.

Enhancing color brilliance and fastness of polyester dyeing with antipyrine-derived disperse dyes

Disperse azo dyes are important colorants for dyeing polyester fabrics, but developing optimized disperse azo dyes remains a challenge. This work details the synthesis of seven new disperse azo dyes 3a-g derived from the coupling reaction of 4-aminoantipyrine diazonium salt with various phenolic precursors including phenol (3a), salicylic acid (3b), salicylaldehyde (3c), cresols (3d-f), and resorcinol (3g). The dyes were characterized by spectroscopic techniques. Their UV–visible absorption spectra were studied, revealing bathochromic shifts for 3d-g containing electron-donating methyl and hydroxyl substituents compared to parent dye 3a while dyes 3b-c showed hypsochromic shifts. The impact of acid and base on the absorption spectra indicates azo-hydrazone tautomerism for 3f-g but predominant azo form for 3a-e. The dyes showed excellent dyeing on polyester fabrics with up to 97.86 % dye exhaustion. High wash, light and perspiration fastness was exhibited while fastness to respiration varied. The strongest color yield on polyester was achieved with 3g derived from resorcinol coupler. Density functional theory calculations were performed to elucidate relationships between substituent effects and spectral attributes. Lower energy gaps were computed for 3f-g, consistent with enhanced reactivity. This work expands disperse azo dye precursors while offering fundamental structure-performance insight to guide future design. The potent polyester coloration and good fastness properties warrant ongoing investigation of these dyes.

Semi-empirical design and synthesis of novel 4-hydroxy-6-sulphonaphthyl azohydroxynaphthalenes with predominant hydrazone form

Due to their enhanced photochromic effects, hydrazone forms of tautomeric azo compounds are commercially preferred as photoreceptors and binary switches. While ortho-hydroxyazo compounds readily exhibit an intramolecular hydrazone re-arrangement, the predominance of hydrazone tautomers of para-hydroxyazo compounds is less frequently observed. The objective of this study was to design and synthesize sulphonated 4-naphthylazo naphth-1-ols with preferential hydrazone shift.PM6 calculations were used to quantify contributions of selected structural features to hydrazone stability in a set of model compounds. Synthesis of five computationally-optimized compounds (3a-e) was subsequently carried out via diazo coupling of 5‑hydroxy-7-sulphonaphthalene-2-diazonium ion with naphthol derivatives. The azo-hydrazone equilibria of 3a-e were further characterized using spectroscopic techniques and density functional theory (DFT).Computational design revealed that sulphonic acid substitution on the coupling components of the dyes and, solvation effect of the substituents were the highest contributors to hydrazone shift of the compounds. The ring position and electron withdrawing resonance effect of substituents were less contributory. Increasing substitution with sulphonic acid or another hydrophilic group (amino) also resulted in higher hydrazone stability. Mass spectral, IR and NMR data confirmed computational results with mono sulphonated 3a and poly substituted 3c-e existing predominantly as azo and hydrazone forms respectively. UV–Visible spectral analysis revealed that azo and hydrazone forms of 3a predominated in hydrogen bond acceptor and donor solvents respectively. In contrast, absorption spectra of 3b-e showed lone hydrazone bands in all solvents investigated. The DFT/M06-2X/6-31G(dp) characterization of the azo-hydrazone equilibrium of the compounds confirmed experimental results and showed that hydrazone tautomers of 3b, 3c and 3d were more stable than corresponding azo forms by 1.536, 0.289 and 1.359 kcal/mol respectively. DFT also confirmed involvement of sulphonic acid and imino groups in the transition of the dyes’ structures to the keto form.Three novel p-hydroxyazo dyes with increased hydrazone stability have been synthesized.

Unraveling Halochromism of Azo‐Based Sulphonamide and Its Real‐World Applications: A Combined Experimental and Theoretical Approach

AbstractHalochromic azo dyes have versatile applications, including sensing and anti‐counterfeiting, due to their reversible color‐changing properties. In this work we investigated the structure‐dependent halochromism of azo compound (E)‐4‐((2‐hydroxynaphthalen‐1‐yl)diazenyl)benzenesulfonamide (HDBS) and explore its potential applications using experimental and theoretical approaches. Different spectroscopic techniques confirm the structural change in the dye as a consequence of tautomerism reaction upon changing pH (7 to 13). The stable form of hydrazone is isolated and characterized. Based on the spectroscopic characterization, it is concluded that the azo form exists at pH ≤ 9, whereas the hydrazone form at highly alkaline pH. To understand the origin of the absorption peaks, the stability, and tautomerism in water, DFT and TD‐DFT calculations are performed. A reasonable agreement between the theoretical and experimental observations enabled us to unravel the structure‐dependent halochromism. Further, we have shown that HDBS‐coated paper can be a real‐time visual sensor to monitor fish freshness and for anti‐counterfeiting ink. It changes colors with pH shifts, alerts consumers about the status of food. Additionally, erasable paper strip reduces paper waste and chemical pollution. The findings presented in this work provide a promising avenue for the development of halochromic azo compounds with potential applications in sensing and anti‐counterfeiting.

D- π-A azo dyes bearing thiazole-diphenylamine units: Synthesis, photophysical and molecular structure properties, and use for dyeing of polyester fabrics

Herein, six new thiazole-dipehenylamine-based azo dyes containing azo and thiazole bridges and diphenylamine donor with different donor/acceptor groups were synthesized. All the synthesized dyes were characterized by FT-IR, NMR and HRMS analyses. The structure of (E)-N-methyl-4-((thiazol-2-yl)diazenyl)-N-phenylaniline (4) was conclusively confirmed by single crystal X-ray diffraction analysis. Photophysical studies were performed in different solvents with various polarity. Although the three synthesized compounds can be represented as potential azo-hydrazone tautomers only the azo form was observed in all solvents used. UV/vis spectroscopic studies showed that the color changed dramatically when the dyes contain a strong electron accepting nitro substituent. Moreover, after protonation of azo dyes, with the exception of the azo dyes with nitro group, a bathochromic shift was observed. The effects of protonation on the geometry and electronic structure of the compounds were studied, and the NLO properties were also investigated using DFT calculations. In addition, the thermal stability of the azo dyes was investigated using thermal gravimetry (TGA). Dyeing performance was evaluated with these dyes on polyester fabric in an aqueous medium. All dyes except dyes 3 and 6 showed good color fastness properties. Therefore, these compounds can be used as textile dyes for polyester fabrics.

15N NMR study of azo-hydrazo tautomerism in some industrially produced azo dyes

15N NMR data (1J (15N, 1H) coupling constants and 15N chemical shifts) were used to characterize quantitatively azo-hydrazo tautomerism in some industrially produced azo dyes. Both 1J (15N, 1H) coupling constants and 15N chemical shifts were obtained at the natural abundance level of 15N using inverse detection of resonances. All three possible types of azo dye existence were found: (i) dyes existing completely in azo forms, (ii) dyes existing completely in hydrazo forms or (iii) dyes forming azo-hydrazo tautomeric equilibria.

Structure of 2-nitro-2’-hydroxy-5’-methylazobenzene: Theoretical and spectroscopic study

Objectives. 2-Hydroxy-nitroazobenzenes comprise reagents for the synthesis of heteroaromatic compounds, in the molecules of which the benzene and azole cycles are annulated. These reagents are widely used in the production of chemical products for various industries. In particular, 2-2’-hydroxy-5’-methylphenylbenzotriazole is used as an effective photo stabilizer for polystyrene and polyethylene. A promising method for its preparation is the liquid-phase catalytic hydrogenation of 2-nitro-2'-hydroxy-5'-methylazobenzene (2NAB). The aim of the present study was to establish the structure of 2NAB in solutions of different composition.Methods. Theoretical calculations were carried out within the framework of the density functional theory at a temperature of 298.15 K for the gas phase at B3LYP/6-311++G(d, p) and M06-2X/6-311++G(d, p) levels; for hexane, 2-propanol, toluene at B3LYP/6-311++G(d, p) level using the conductor-like polarizable continuum model. An experimental study to determine the probable isomeric structure of 2NAB in various solvents, including sodium hydroxide (NaOH) and acetic acid (CH3COOH) additives, was carried out using infrared (IR) and ultraviolet (UV) spectroscopy.Results. The most probable structure of 2NAB isomers for the gas phase and a number of solvents was determined. Experimental and theoretical IR and UV spectra were obtained. The thermodynamic characteristics of the reaction of intramolecular proton transfer from –OH to –N=N– group in the gas phase were calculated.Conclusions. A comparison of the experimental and calculated results supports the conclusion that the cis-isomer should be considered most probable for the gas phase. For the studied solutions, a trans-isomer of 2NAB with hydrogen bonds formed between the hydroxyl group hydrogen and the β-nitrogen atom of the azo group of dye molecule should be considered as the most likely structure. In the studied individual and binary solvents, prototropic equilibrium is shifted towards the azo form of the dye, while intramolecular proton transfer is possible only in aqueous diethylamine and dimethylformamide solutions with additions of NaOH.

Structure of 2-nitro-2’-hydroxy-5’-methylazobenzene: Theoretical and spectroscopic study

Objectives. 2-Hydroxy-nitroazobenzenes comprise reagents for the synthesis of heteroaromatic compounds, in the molecules of which the benzene and azole cycles are annulated. These reagents are widely used in the production of chemical products for various industries. In particular, 2-2’-hydroxy-5’-methylphenylbenzotriazole is used as an effective photo stabilizer for polystyrene and polyethylene. A promising method for its preparation is the liquid-phase catalytic hydrogenation of 2-nitro-2'-hydroxy-5'-methylazobenzene (2NAB). The aim of the present study was to establish the structure of 2NAB in solutions of different composition.Methods. Theoretical calculations were carried out within the framework of the density functional theory at a temperature of 298.15 K for the gas phase at B3LYP/6-311++G(d, p) and M06-2X/6-311++G(d, p) levels; for hexane, 2-propanol, toluene at B3LYP/6-311++G(d, p) level using the conductor-like polarizable continuum model. An experimental study to determine the probable isomeric structure of 2NAB in various solvents, including sodium hydroxide (NaOH) and acetic acid (CH3COOH) additives, was carried out using infrared (IR) and ultraviolet (UV) spectroscopy.Results. The most probable structure of 2NAB isomers for the gas phase and a number of solvents was determined. Experimental and theoretical IR and UV spectra were obtained. The thermodynamic characteristics of the reaction of intramolecular proton transfer from –OH to –N=N– group in the gas phase were calculated.Conclusions. A comparison of the experimental and calculated results supports the conclusion that the cis-isomer should be considered most probable for the gas phase. For the studied solutions, a trans-isomer of 2NAB with hydrogen bonds formed between the hydroxyl group hydrogen and the β-nitrogen atom of the azo group of dye molecule should be considered as the most likely structure. In the studied individual and binary solvents, prototropic equilibrium is shifted towards the azo form of the dye, while intramolecular proton transfer is possible only in aqueous diethylamine and dimethylformamide solutions with additions of NaOH.

Reversal in solvatochromism, photochromism and thermochromism in a new bis-azo dye based on naphthalen-1-amine

A novel bis-azo dye, 4,4′-((1E,1′E)-(oxybis(4,1-phenylene))bis(diazene-2,1-diyl))bis(naphthalen-1-amine) (abbreviated as 4odna) was synthesized and characterized by IR and 1H, 13C and 2D COSY-NMR spectroscopies, and mass spectrometry. Optical properties were evaluated using UV–vis absorption spectroscopy. The observed solvatochromism was ascribed to the presence of different azo or/and hydrazone forms in solution. The azo forms show both positive and negative solvatochromism, with the reversal occurring for solvents with ET(30) ∼45 kcal mol−1, while the hydrazone tautomer shows negative solvatochromism. Application of the multiparametric Catalán and Kamlet-Taft linear solvation energy models allowed to evaluate the dependence of the solvatochromism exhibited by 4odna on the hydrogen bond donating (HBD) and accepting (HBA) abilities of the solvent, as well as on their dipolarity (SdP) and polarizability (SP). Upon UV (λ = 311 nm) irradiation at room temperature, the compound was found to exhibit similar photochromic behavior in the polar-protic solvents methanol and ethanol, which is distinct from that observed in the polar-aprotic solvents dichloromethane, chloroform and chlorobenzene, with the hydrazone tautomer being photoconverted into the azo tautomer in the first group of solvents and vice-versa in the second group. In acetone, UV irradiation extensively transforms the compound into species with no absorption in the visible range, leading to fast discoloration of the solution. Temperature dependence of the color of the solutions of 4odna in ethanol and chlorobenzene was also evaluated, and reversible thermochromic behavior was observed in the first solvent. In chlorobenzene, no thermochromism was observed, but a change of color of the solution was promptly induced by the UV–vis broadband source beam of the spectrometer when the absorbance spectrum of the solution was being recorded at T = 115 °C, which demonstrates that the azo forms of 4odna undergo easy phototransformation into the hydrazone forms in this solvent at high temperature.

Thiadiazole Functionalized Salicylaldehyde-Schiff Base as a pH-responsive and chemo-reversible "Turn-Off" fluorescent probe for selective cu (II) detection: Logic Gate Behaviour and Molecular Docking Studies.

A novel thiadiazole functionalized schiff base chemoreceptor (E)-2,4-dichloro-6-(((5-mercapto-1,3,4-thiadiazol-2-yl)imino)methyl)phenol (SB-1) has been synthesized and characterized spectroscopically by using various techniques. Its photophysical behaviour was scanned towards a variety of metal ions in mixed aqueous media. The chemosensor (SB-1) displayed excellent selectivity towards Cu2+ ion through fluorescent diminishment (turn-off phenomenon). Colorimetric analyses showed a rapid colour change from yellow to dark red under visible light upon addition of Cu2+ ions. Interestingly, the original yellow colour reappeared back instantly after the addition of EDTA2- anions, thus confirming the reversible nature of SB-1. Competitive experiments validated no interference from the other co-existing metal ions in the recognition process of SB-1 towards Cu2+ ion. Job's plot confirmed 1:1 binding stoichiometry between SB-1 and Cu2+ ion with the binding constant value of 3.87 × 104M- 1. The limit of detection was determined to be 1.01 × 10- 7M suggesting good sensitivity of SB-1 towards Cu2+ ions. Furthermore, pH-dependent UV-Vis spectral behaviour of SB-1 confirmed that it could act as an effective optical pH-sensor for highly acidic environment as well. Portable nature of probe SB-1 was explored by fabricating "easy-to-use" paper test strips, which allow robust and rapid detection of Cu2+ ions. Based on the multi-responsive properties of SB-1, a 'NOR' logic gate was constructed by applying Cu2+ and EDTA2- as chemical inputs (ln1: Cu2+, ln2: EDTA2-) while emission intensity observed at 560nm was considered as output signal (O1). DFT optimized geometries confirmed that chemosensor SB-1 exists in Azo form (Enol form) in its ground state. Molecular docking of the SB-1 and its copper complex, into the binding site of TRK protein tyrosine kinase (PDB: 1t46) was also carried out to explore their biological activity and their potential use as TRK inhibitors.

Solvent- and Light-Sensitive AIEE-Active Azo Dye: From Spherical to 1D and 2D Assemblies.

Fluorescent molecular assembly systems provide an exciting platform for creating stimuli-responsive nano- and microstructured materials with optical, electronic, and sensing functions. To understand the relationship between (i) the plausible molecular structures preferentially adopted depending on the solvent polarity (such as N,N-dimethylformamide [DMF], tetrahydrofuran [THF], and toluene), (ii) the resulting spectroscopic features, and (iii) self-assembled nano-, micro-, and macrostructures, we chose a sterically crowded triangular azo dye (3Bu) composed of a polar molecular core and three peripheral biphenyl wings. The chromophore changed the solution color from yellow to pink-red depending on the solvent polarity. In a yellow DMF solution, a considerable amount of the twisted azo form could be kept stable with the help of favorable intermolecular interactions with the solvent molecules. By varying the concentration of the DMF solution, the morphology of self-assembled structures was transformed from nanoparticles to micrometer-sized one-dimensional (1D) structures such as sticks and fibers. In a pink-red toluene solution, the periphery of the central ring became more planar. The resulting significant amount of the keto-hydrazone tautomer grew into micro- and millimeter-sized 1D structures. Interestingly, when THF-H2O (1:1) mixtures were stored at a low temperature, elongated fibers were stacked sideways and eventually developed into anisotropic two-dimensional (2D) sheets. Notably, subsequent exposure of visible-light-irradiated sphere samples to solvent vapor resulted in reversible fluorescence off↔on switching accompanied by morphological restoration. These findings suggest that rational selection of organic dyes, solvents, and light is important for developing reusable fluorescent materials.

A pH-activated fluorescent probe via transformation of azo and hydrazone forms for lysosomal pH imaging.

We developed a fluorescent probe Sth-NH by introducing a 6-hydroxypyridone skeleton. The presence of an active proton enables the probe to transform from a deprotonated azo form to a hydrazone form in a strongly acidic environment to realize fluorescence light-up behavior, thus monitoring the lower lysosomal pH of cancer cells and distinguishing them from normal cells.

UV–VIS investigation of methyl red in presence of sodium dodecyl sulfate/methanol/ethanol/water system

This paper reports room temperature UV–VIS study of interaction of methyl red (MR) dye with sodium dodecyl sulfate (SDS)/methanol/ethanol/water systems in different ratios of the solvent components (R = 0, 10, 20, 30, and 40); where the concentration of water is represented by a R parameter. The concentration of SDS was varied from 1.4 × 10-4 to 2.8 × 10-3molL-1 for the SDS/methanol/water system and 2.2 × 10-4 to 4.4 × 10-3molL-1 for SDS/ethanol/water system. In all experiments, MR concentration was fixed to 7.4 × 10-6molL-1. The MR spectrum was very similar at lower R values. The solution appeared cloudy at R = 30. For R = 40, MR absorption maximum (λmax) strongly red-shifted from 412 nm to 493–495 nm on increasing the concentration of SDS in the methanol system but no such shift was observed in ethanol. The transparency of the solution again vanished at R = 50 and the experiment was not carried above. These observations suggested that MR exists in hydrazone and azo form in SDS/methanol and SDS/ethanol system; respectively. On increasing concentration of SDS, the MR absorbance increased in the methanol system (hyperchromic shift) and decreased in ethanol system (hypochromic shift). The distribution constant (K) and binding constant (K’) were evaluated through the NLREG procedure and the modified Benesi-Hildebrand equation was also introduced to calculate the binding constant (Kb) and Gibbs free energy of binding (ΔG0). With increasing R, the ΔG0 value became more negative in methanol system; whereas it became less negative in the ethanol system. The negative value of ΔG0 indicated the spontaneity of SDS binding with MR.

A new derivative of 8-hydroxyquinoline. Features of distribution and complexation with Cu(II) and Zn(II) in two-phase systems

ABSTRACT A new promising analytical reagent is proposed for the extractive recovery of Cu(II) and Zn(II). The reagent is produced upon azo coupling of 8-hydroxyquinoline with diazotized 4-(prop-2-yn-1-yloxy)aniline in yield of 54%. Its structure was confirmed by the combined data from IR, 1Н, and 13С NMR spectroscopy, and HRMS. The UV-VIS absorption spectra suggests an azo-hydrazone tautomerism to exist in the 2-ethoxyethanol medium and 5-(4-(prop-2-ynyloxy)phenylazo)quinolin-8-ol to be present in a chloroform or acetonitrile solution predominantly as the azo form. The extraction behavior of 5-(4-(prop-2-ynyloxy)phenylazo)quinoline-8-ol with regard to Cu(II) and Zn(II) in a chloroform–water system was studied. The stoichiometry of the extracted complex compounds and the conditional extraction constant were calculated.

Fenton-like reactions for pyrazolone ester based heterocyclic dyes with reversible hydrazone-azo tautomerism

In this work, two new pyrazolone ester based heterocyclic hydrazone dyes have been prepared and characterized by NMR, FT-IR and MS spectrometry. The acid/base-activated hydrazone-azo tautomerism has been monitored by UV–Vis and 1H NMR spectra. It is worth mentioning that three Fenton catalysts: CuII, NiII and CoII are introduced to form reactive hydroxyl radicals from hydrogen peroxide to attack the ortho-position of phenyl unit of one pyrazolone ester based heterocyclic dye, and resulted in another ortho-OH substituted pyrazolone ester based heterocyclic dye via CuII/NiII/CoII-H2O2 catalytic oxidation, metal-ion complexation, and ending demetallization. Furthermore, three CuII, NiII and CoII centered complexes have been isolated and structurally characterized including the resultant heterocyclic dye as the anionic ligand. UV–Vis spectral comparisons show that the absorption maximum (λmax) values of CuII, NiII and CoII centered complexes are significantly shifted to higher wavelengths compared to their common precursor. This is originated from the increased electron density by forming the divalent L2− ligand, which is comparable to the pyrazolone ester based heterocyclic dye in deprotonation azo form under alkaline condition. Furthermore, the hydrazone-azo tautomerism has been verified by the significant changes of hydrazone proton signals observed in the 1H NMR spectra. In addition, two possible pathways for Fenton catalysts corresponding to three types of metal ions were proposed. We believe that the acquisition of these intermediate metal complexes is conducive to understanding on the applications of Fenton-like reactions in the syntheses of heterocyclic dyes.

Electronic transport behavior of 1-(Phenyldiazenyl)naphthalen-2-ol and its derivatives as optical molecular switches: A first-principles approach

We studied the electronic transportation properties of 1-(Phenyldiazenyl)naphthalen-2-ol and its derivatives, as optical molecular switches, by using the nonequilibrium Green’s function (NEGF) formalism combined with the first-principles density functional theory (DFT). To describe this switching, we applied the geometrical and topological parameters, Time-dependent density functional theory (TD-DFT), and the second-order interaction energies, E(2), results. The mentioned switching for titled molecules occurred between their tautomers, hydrazo and azo forms, upon photoexcitation. According to our results the current rate of titled molecules is more than that the other reported molecules, about 40,000 nA. Therefore, titled molecules show appropriate potential for using in molecular switch tools. The transmittance spectra and I–V curves show the current of the azo tautomer is more than that in the hydrazo tautomer. This result agree with increasing of the intramolecular hydrogen bond strength, electron densities of aromatic and chelated rings, and the hyperconjugations in the azo forms. In addition, the −OCH3 and -NO2 groups, does not remarkably affected the current rate with Y (111) (Y =Au, Ag, and Pt) electrodes. The best performance obtained in Ag electrode, in while in the other reported molecular switchers Au electrode was appropriated.

The spectral study of azo dye and cationic surfactant interaction in ethanol-water mixture

The interaction of the azo dye methyl red (MR) with dodecyl trimethyl ammonium bromide (DTAB) has been studied by the spectrometric methods through the azo-hydrazone tautomeric behaviour of MR for a series of the ethanol?water system (0.1, 0.2, 0.3 and 0.4 volume fractions of ethanol) at room temperature. The critical micelle concentration was determined using the conductometric technique with the increased ethanol volume, influenced by the solvent polarity and the architectural flexibility of methyl red. The azo form of methyl red brings the electrostatic interaction with the cationic surfactant through the adsorption phenomenon. The binding parameters were calculated with the aid of a modified Benesi?Hildebrand equation.

Fenton-Like Reactions for Pyrazolone Ester Based Heterocyclic Dyes with Reversible Hydrazone-Azo Tautomerism

In this work, two new pyrazolone ester based heterocyclic hydrazone dyes have been prepared and characterized by NMR, FT-IR and MS spectrometry. The acid/base-activated hydrazone-azo tautomerism has been monitored by UV-Vis and 1 H NMR spectra. What is worth mentioning, three Fenton catalysts: Cu II , Ni II and Co II are introduced to form reactive hydroxyl radicals from hydrogen peroxide to attack the ortho -position of phenyl unit of one pyrazolone ester based heterocyclic dye and resulted in another ortho -OH substituted pyrazolone ester based heterocyclic dye via Cu II /Ni II /Co II -H 2 O 2 catalytic oxidation, metal-ion complexation, and ending demetallization. Furthermore, three Cu II , Ni II and Co II centered complexes have been isolated and structurally characterized including the resultant heterocyclic dye as the anionic ligand. UV-Vis spectral comparisons show that the absorption maximum ( λ max ) values of Cu II , Ni II and Co II centred complexes are significantly shifted to higher wavelengths compared to their precursor, originated from the increased electron density by forming the divalent L 2- ligand in the deprotonated azo form, which is comparable to the pyrazolone ester based heterocyclic dye in deprotonation azo form under alkaline condition. Furthermore, the hydrazone-azo tautomerism has been verified by the significant changes of hydrazone proton signals observed in the 1 H NMR spectra. In addition, two possible pathways for Fenton catalysts corresponding to three types of metal ions were proposed. We believe that the acquisition of these intermediate metal complexes is conducive to understanding on the applications of Fenton-like reactions in the syntheses of heterocyclic dyes.

Effect of hydrogen-bond strength on photoresponsive properties of polymer-azobenzene complexes

Supramolecular complexation between photoresponsive azobenzene chromophores and a photopassive polymer host offers synthetic and design advantages compared with conventional covalent azo-containing polymers. In this context, it is important to understand the impact of the strength of the supramolecular interaction on the optical response. Herein, we study the effect of hydrogen-bonding strength between a photopassive polymer host [poly(4-vinylpyridine), or P4VP] and three azobenzene analogues capable of forming weaker (hydroxyl), stronger (carboxylic acid), or no H-bonding with P4VP. The hydroxyl-functionalized azo forms complete H-bonding complexation up to equimolar ratio with VP, whereas the COOH-functionalized azo reaches only up to 30% H-bond complexation due to competing acid dimerization that leads to partial phase separation and azo crystallization. We show that the stronger azo-polymer H-bonding nevertheless provides higher photoinduced orientation and better performance during optical surface patterning, in terms of grating depth and diffraction efficiency, when phase separation is either avoided altogether or is limited by using relatively low azo contents. These results demonstrate the importance of the H-bonding strength on the photoresponse of azopolymer complexes, as well as the need to consider the interplay between different intermolecular interactions that can affect complexation.

Experimental and theoretical studies on monoazo dye including diphenylamine and N-methyldiphenylamine derivatives

In this manuscript, two series of azo dyes preparing by coupling diphenylamine and N-methyl diphenylamine and diazotized substituted anilines bearing various substituents were designed and synthesized. These azo dyes were characterized by spectroscopic techniques such as 1H/13C NMR and HRMS or LCMS. Photophysical, NLO and protonation properties were investigated by experimentally and theoretically. The absorption maxima were observed in long wavelength in DMSO. The most stable tautomeric form of dyes which have tautomeric forms, were determined using model compounds. The results showed that the azo dyes are stable in azo form in all solvents used. For the usability as optic dye of the synthesized dyes, thermal property of all dyes was also determined. The all compounds are thermally stable and Td values are bigger than 220 °C.