Azo Chromophores Research Articles

The "Tethered Solvent" Effect - H-Bonding-Controlled Thermo-Halochromism of a Push-Pull Azo Chromophore via Its Secondary Amidoalkyl Acrylamide Side Chain.

The fascinating field of thermo-halochromism of azo chromophores still astounds with unexplored facets nourished by the intricate relationship between molecular structure variations and their spectroscopic signatures. In this respect, we investigated the thermally dependent absorption behaviour of acrylamide derivatives of o-methyl red, characterised by two secondary amide linkages with hydrogen bonding-active protons in the pendant alkyl substituent. The systems were studied by a combination of UV-vis, derivative, and difference, as well as 2D-NMR (Nuclear Overhauser Effect Spectroscopy, NOESY) spectroscopy. These experiments show that the thermo-halochromism is specifically influenced by hydrogen bonding interaction of the secondary amidoalkyl acrylamide side chain with the azobenzene core in dependence of the spacer length. Apparently, the substituent acts like a solvent, which is directly tethered to the chromophore and where the tether length determines the interaction by conformational freedom. We refer to this novel phenomenon as "H-bonding-controlled thermo-halochromism".

High-Transparency and Colorless Polyimide Film Prepared by Inhibiting the Formation of Chromophores.

Colorless polyimides (CPIs) with outstanding mechanical properties are essential materials in the production of flexible display panels, foldable windows, and even spacecraft cockpits. This paper specifically elaborates that the Morkit unit, and azo and nitro chromophores are important factors contributing to yellow PI, together with the well-known charge transfer complex (CTC) theory. Three diamine monomers, two anhydrides monomers, and three blockers were used to inhibit chromophores formation and, thus, obtain CPI films. The cut-off wavelength was blue-shifts to 334 nm and the transmittance is improved to 98.9% in the UV–vis range. Mechanical and thermal properties of the CPI films are not reduced through coupling effects of the blockers. Therefore, the inhibition method of the Morkit units and chromophore groups is a promising process for preparing CPIs to be used as flexible display materials.

Bimetallic Co-Fe-BTC/CN nanocomposite synthesised via a microwave-assisted hydrothermal method for highly efficient Reactive Yellow 145 dye photodegradation

BackgroundReactive Yellow 145 (RY-145), a common organic dye-containing azo chromophore found in wastewater from the textile and printing industries, can cause serious environmental pollution and pose a huge threat to human beings and various natural organisms. MethodsWe herein introduce for the first time a nanocomposite based on a bimetallic Co-Fe-BTC metal-organic framework (MOF) and a graphitic carbon nitride (CN) using a microwave-assisted hydrothermal method. It was shown that the Co-Fe-BTC/CN nanocomposite with band-gap energies of 2.38–2.52 eV and photocurrent intensity of 0.352 mA/cm2 can effectively excite photosensitive reaction and improve ion transport and electrolyte diffusion. Significant findingsThe performance of this nanocomposite material was examined in the decomposition of Reactive Yellow 145 (RY-145) dye under sunlight irradiation. The factors which might affect the dye removal process including Co:Fe molar ratio, dye concentration, pH, catalyst dosage and reaction radicals were evaluated. Based on the electrochemical data, we have been able to propose the mechanism and provide an insightful study of the photodegradation process. Our results also demonstrated that the nanocomposite sample with Co2-Fe8-BTC/CN doping exhibited excellent photocatalytic activity with 99.38% of RY-145 degradation after 40 min, as compared to Co-BTC/CN (89.76%) and Fe-BTC/CN (93.68%).

Towards passive bioremediation of dye-bearing effluents using hydrous ferric oxide wastes: Mechanisms, products and microbiology

A novel, circular economy-inspired approach for the “passive” (non-powered and reagent-free) treatment of dye-bearing effluent is presented. The treatment utilises the biogeochemical interaction of dye-bearing wastewater with hydrous ferric oxide (HFO) bearing sludges. The work presented demonstrates for the first time the reuse of HFO-rich waste sludges from potable water and mine water treatment. The waste was used directly without modification or reagent addition, as media/substrate in simple flow-through reactors for the decolourisation and biodegradation of methyl orange (MO) and mixed dyes textile effluent. Three phases of exploratory proof of concept work were undertaken. Columns containing HFO sludges were challenged with solution of MO, and MO amended with glycerol (Phase I), MO in a synthetic textile effluent recipe (Phase II), and real mixed textile effluent containing a mixture of dyes (Phase III). After an initial lag period extensive decolourisation of dye was observed in all cases at rates comparable with pure strains and engineered bioreactor processes, with evidence of biodegradation beyond simple cleavage of the mono azo chromophore and mineralisation. The microbiology of the initial sludge samples in both cases exhibited a diverse range of iron oxidising and reducing bacteria. However, post experiment the microbiology of sludge evolved from being dominated by Proteobacteria to being dominated by Firmicutes. Distinct changes in the microbial community structure were observed in post-treatment MWTS and WTWS where genera capable of iron and sulphate reduction and/or aromatic amine degradation were identified. Average nitrogen removal rates for the columns ranged from 27.8 to 194 g/m3/day which is higher than engineered sequential anaerobic-aerobic bioreactor. Postulated mechanisms for the fast anaerobic decolourisation, biodegradation, and mineralisation of the dyes (as well nitrogen transformations) include various direct and indirect enzymatic and metabolic reactions, as well as reductive attack by continuously regenerated reductants such as Fe(II), HFO bound Fe(II), FeS, and HS−. The ability of iron reducers to degrade aromatic rings is also considered important in the further biodegradation and complete mineralisation of organic carbon. The study reveals that abundant and ubiquitous HFO-rich waste sludges, can be used without amendment, as a substrate in simple flow-through bioremediation system for the decolourisation and partial biodegradation of dyes in textile effluent.

Design and synthesis of diazirine‐containing dyes for polypropylene fibre: A study on the effect of alkyl chain

AbstractThe dyeing of polypropylene fabrics utilising conventional‐disperse dyes often meets poor colour yield and fastness problems, fundamentally caused by the low affinity between dyes and polypropylene fibres. In this article, a new class of hydrophobic reactive dyes that can react with polypropylene were designed using diazirine moiety as a reactive group, azo structure as a chromophore, and an ester group as a linking bridge. The difference among these dyes was the alkyl chain length on the azo chromophore, which was used to fine‐tune the affinity between the dyes and fibre. The structures of the synthesised dyes and intermediates were characterised and confirmed using nuclear magnetic resonance, mass spectrometry, and infrared spectrometry. The absorption and thermal properties of the dyes were also studied to ensure their feasibility for dyeing application. In addition, the diazirine dyes were successfully applied to dye polypropylene fabrics using a two‐step process by dyeing in a non‐aqueous solvent and fixing it under heating. The dyes and polypropylene fibre were demonstrated to react, where the fixation values were in the range 64.5–76.4%. The systematic study of the structure–property relationship demonstrated the positive effect of the alkyl chain in promoting colour yield, however, accompanied by a slightly reduced fixation value. Due to the chemical bonding of the dye molecules to the fibre, the dyed polypropylene fabrics exhibited excellent colour fastness property, making the dyeing technology very promising for future industrial applications.

Novel and Sustainable Colorants Developed via Incorporating Azo Chromophores into Dopamine Molecules.

Inspired by the application of dopamine as an “anchor” and UV absorber, novel sustainable colorants with biscatecholic structure were synthesized through a simple incorporation of simple azo chromophores with dopamine. Their structures were confirmed using MS and NMR analyses, and their application on textile materials was investigated. Compared to the simple azo chromophores with almost no coloring ability on fabrics, the biscatecholic colorants could color different fabrics effectively, mainly through self-polymerization only in the presence of a trace amount of organic base at room temperature, which is environmentally friendly in terms of saving resources and alleviating chemical pollution. Meanwhile, the UV resistance of colored fabrics was enhanced significantly, showing the advantage of protecting wearers from UV damage.

A DFT analysis of electronic, reactivity, and NLO responses of a reactive orange dye: the role of Hartree-Fock exchange corrections.

An experimental and theoretical study based on DFT/TD-DFT approximations is presented to understand the nature of electronic excitations, reactivity, and nonlinear optical (NLO) properties of reactive orange 16 dye (RO16), an azo chromophore widely used in textile and pharmacological industries. The results show that the solvent has a considerable influence on the electronic properties of the material. According to experimental results, the absorption spectrum is formed by four intense transitions, which have been identified as [Formula: see text] states using TD-DFT calculations. However, the TD-DFT results reveal a weak [Formula: see text] in the low-lying spectral region. Continuum models of solvation indicate that these states suffer from bathochromic (ca. 15 nm) and hypsochromic shifts (ca. 4 nm), respectively. However, the expected blue shift for the absorption [Formula: see text] is only described using long-range or dispersion-corrected DFT methods. RO16 is classified as a strong electrophilic system, with electrophilicity ω > 1.5 eV. Concerning the nucleophilicity parameter (N), from vacuum to solvent, the environment is active and changes the nucleophilic status from strong to moderate nucleophile (2.0 ≤ N ≤ 3.0 eV). The results also suggest that all electrical constants are strongly dependent on long-range and Hartree-Fock exchange contributions, and the absence of these interactions gives results far from reality. In particular, the results for the NLO response show that the chromophore presents a potential application in this field with a low refractive index and first hyperpolarizability ca. 214 times bigger than the value usually reported for urea (β = 0.34 × 10- 30 esu), which is a standard NLO material. Concerning the solvent effects, the results indicate that the polarizability increases [Formula: see text] esu from gas to solvent while the first hyperpolarizability is calculated as [Formula: see text] esu, ca. 180%, regarding the vacuum. The results suggest RO16 is a potential compound in NLO applications. Graphical Abstract The frontier molecular orbitals, and the inverse relation between the energy-gap (Egap) and the first hyperpolarizability (β).

Reversible Controlling the Supramolecular Chirality of Side Chain Azobenzene Polymers: Chiral Induction and Modulation.

Chirality represents a fundamental structure in nature and the induction and reversible modulation of supramolecular chirality with feasible techniques is of great value in the design of new chiroptical smart materials. Herein, two kinds of azobenzene side-chain polymers (without spacer: Azo-PMA0; with 6 spacers: Azo-PMA6) are synthesized, the length of spacer and azobenzene chromophores play a vital role in chirality transfer and modulation. The supramolecular chiral arrangement of Azo-PMA0 (amorphous phase) can be completely controlled and reversibly modulated over multiple cycles by 450nm circularly polarized light driven by the supramolecular interaction between azo groups of polymer chains, with an absorption dissymmetry factor (g) value of 0.0019. The chiroptical properties of Azo-PMA6 (liquid crystal state) can also be reversibly modulated by UV light and thermal annealing treatment during trans-cis isomerization of azo chromophore, with the g-value changes from 0-0.038. The successful construction of reversible chiral induction and modulation based on side chain azobenzene polymers may pave the way for designing photo-switchable functional materials.

Photoswitches with different numbers of azo chromophores for molecular solar thermal storage.

We investigate three azo-chromophore-containing photoswitches (1, 2 and 3) for molecular solar thermal storage (MOST) based on reversible Z-E isomerization. 1, 2 and 3 are photoswitchable compounds that contain one, two and three azo chromophores, respectively. In solution, 1, 2 and 3 were charged via UV-light-induced E-to-Z isomerization. Among these three compounds, 2 exhibited an energy density as high as 272 ± 1.8 J g-1, which showed the best energy storage performance. This result originated from the low molecular weight, a high degree of photoisomerization, and moderate steric hindrance of 2, which demonstrated the advantages of the meta-bisazobenzene structure for MOST. In addition, we studied the performances of these photoswitches in the solvent-free state. Only 1 showed photoinduced reversible solid-to-liquid transitions, which enabled the charging of 1 in a solvent-free state. The stored energy density for 1 in a solvent-free state was 237 ± 1.5 J g-1. By contrast, 2 and 3 could not be charged in the solvent-free state due to the lack of solid-state photoisomerization. Our findings provide a better understanding of the structure-performance relationship for azobenzenebased MOST and pave the way for the development of high-density solar thermal fuels.

Electro-Optical Properties of Polymethacrylate with a Covalently Bound Azo Chromophore

Electro-Optical Properties of Polymethacrylate with a Covalently Bound Azo Chromophore

Triphasic Polymer Particles Assembled via Microphase Separation with Multiple Functions.

This work investigated a unique type of triphasic colloidal particles composed of an azo polymer (PCNAZO), a fluorescent pyrene-containing polymer [P(MMA-co-PyMA)], and a poly(dimethylsiloxane)-based polymer (H2pdca-PDMS), focusing on the synthesis, forming mechanism, morphology control, and functions. The triphasic particles with well-defined morphologies were assembled through the microphase separation of the components in dichloromethane (DCM) droplets in an aqueous medium, induced by the gradual evaporation of the organic solvent. The real-time fluorescence emission spectra of the pyrenyl moieties and in situ microscopic observations show that the formation of the triphasic particles undergoes the segregation of the PCNAZO-rich phase, separation between P(MMA-co-PyMA)-rich and H2pdca-PDMS-rich phases, coalescence, and solidification in the dispersed droplets. The structure formation is due to the strong phase separation of the polymers as revealed by the calculations based on the Flory-Huggins theory. The morphologies and phase boundaries of the particles are found to be controlled by the interfacial energy between the phases and processing conditions. The triphasic particles thus obtained possess a series of interesting functions stemming from the polymers and the triple-compartmentalized structures. After being deposited on a substrate, the H2pdca-PDMS parts can tightly adhere on the surface, caused by the spreading nature of the polymer when slightly swelled by DCM. Upon irradiation with a linearly polarized laser beam at 488 nm, the azo polymer compartments show a significant elongation along the electric vibration direction of the polarized light, accompanied by the cooperative deformation of the H2pdca-PDMS pads. When dispersed in water and adhered on the substrate surface, the triphasic particles exhibit tunable colors originating from the fluorescence of the pyrenyl fluorophores and light absorption of the azo chromophores. The real-time investigation methods developed here could lead to the deep understanding of the structure formation process in the confined volume and be applied in phase-separation study of other polymers as well.

Enhancing Single-Crystal Dichroism of an Asymmetric Azo Chromophore by Perfluorophenyl Embraces and Boron Coordination

We describe the use of perfluorophenyl embraces and boron coordination (B ← N) to enhance dichroism in single crystals of an asymmetric azo chromophore. Specifically, a tripod-shaped boron adduct c...

A New Family of Benzo[h]Chromene Based Azo Dye: Synthesis, In-Silico and DFT Studies with In Vitro Antimicrobial and Antiproliferative Assessment.

The high biological activity of the chromene compounds coupled with the intriguing optical features of azo chromophores prompted our desire to construct novel derivatives of chromene incorporating azo moieties 4a-l, which have been prepared via a three-component reaction of 1-naphthalenol-4-[(4-ethoxyphenyl) azo], 1, with the benzaldehyde derivatives and malononitrile. The structural identities of the azo-chromene 4a-l were confirmed on the basis of their spectral data and elemental analysis, and a UV–visible study was performed in a Dimethylformamide (DMF) solution for these molecules. Additionally, the antimicrobial activity was investigated against four human pathogens (Gram-positive and Gram-negative bacteria) and four fungi, employing an agar well diffusion method, with their minimum inhibitory concentrations being reported. Molecules 4a, 4g, and 4h were discovered to be more efficacious against Syncephalastrum racemosum (RCMB 05922) in comparison to the reference drugs, while compounds 4b and 4h demonstrated the highest inhibitory activity against Escherichia coli (E. coli) in evaluation against the reference drugs. Moreover, their cytotoxicity was assessed against three different human cell lines, including human colon carcinoma (HCT-116), human hepatocellular carcinoma (HepG-2), and human breast adenocarcinoma (MCF-7) with a selection of molecules illustrating potency against the HCT-116 and MCF-7 cell lines. Furthermore, the molecular modeling results depicted the binding interactions of the synthesized compounds 3b and 3h in the active site of the E. coli DNA gyrase B enzyme with a clear SAR (structure–activity relationship) analysis. Lastly, the density functional theory’s (DFTs) theoretical calculations were performed to quantify the energy levels of the Frontier Molecular Orbitals (FMOs) and their energy gaps, dipole moments, and molecular electrostatic potentials. These data were utilized in the chemical descriptor estimations to confirm the biological activity.

Azo chromophores for nonlinear-optical application

The review covered the works published after 2000 and is devoted to the synthesis of azo chromophores with nonlinear optical (NLO) properties that were estimated experimentally or theoretically. Since NLO properties are manly exhibited by the polymeric materials, the clear understanding of the paths leading to symbiotic relationship between azo chromophore and polymer is required. New strategy to the NLO materials involves the introduction of the guest chromophores into the azo chromophore-containing dendritic polymer host, namely, the use of two different chromophores in the same polymer matrix.

Mussel-like Surface Adhesion and Photoinduced Cooperative Deformation of Janus Particles.

This study focused on mussel-like surface adhesion and photoinduced cooperative deformation of a unique type of Janus particles (JPs), composed of an isosorbide-based molecular glass bearing push-pull type azo chromophore (IAC-4) and a 2,6-pyridinedicarboxamide-containing poly(dimethylsiloxane) oligomer (H2pdca-PDMS). The JPs were obtained by the solvent evaporation method in an aqueous medium with the dispersed phase of a solution of IAC-4 and H2pdca-PDMS in dichloromethane (DCM). The JP formation and its mechanism were investigated by electron microscopy, in situ optical microscopy, and theoretical analysis. The results showed that the Janus structures form through gradual segregation between the two components in the droplets induced by the evaporation of DCM, which follows the ternary phase diagrams calculated according to Flory-Huggins theory. In the following stage, the gradual coalescence of small domains in droplets is controlled by dynamic factors. After being deposited on a substrate, the JPs exhibit unidirectional adhesion with the H2pdca-PDMS parts spreading on the substrate, while the IAC-4 parts orientate away from the substrate. The mussel-like adhesion is caused by the interfacial interaction of H2pdca-PDMS with the hard surfaces (i.e., glass and silicon substrates) and its strong ability to spread and wet the surfaces to increase the contact area with the surfaces. Upon irradiation with linearly and circularly polarized laser beams at 488 nm, respectively, a series of unique surface morphologies are observed because of the photoinduced deformation of the IAC-4 parts along the electric vibration direction of the polarized light and the cooperative deformation of the H2pdca-PDMS parts of the JPs. The cooperative deformation reveals the strong interfacial interaction and cohesiveness between the IAC-4 and the H2pdca-PDMS phases in JPs. No peeling-off from the substrate is observed after the large-scale deformation, which also indicates the strong adhesion of the JPs on the substrate surfaces. This study not only demonstrates the mussel-like adhesion and unique cooperative deformation behavior but also supplies new insights into the interfacial interaction in JPs as well as that with hard surfaces, thus opening a new avenue for surface modification and functionalization.

Investigation of the Treatment of Textile Wastewater with Cold Atmospheric Plasma Reactor (Profoks) and Reuse of Recycled Water in Reactive Dyeing Process of Cotton

ABSTRACT In this study, Profoks reactor (Cold Atmospheric Plasma reactor based on Dielelectric Barrier Discharge) was used for the treatment of textile wastewater and then the usability of the recycled water in the reactive dyeing process was investigated. After processing of 30 L textile wastewater with Profoks system under laboratory conditions, 99% efficiency was obtained in chemical oxygen demand (COD) and total suspended solid (TSS) parameters. In the wastewater sample, the treated water color amount was reduced to less than 1.5 units in Pt-Co and the conductivity value was reduced to 7790 Us/cm. In dyeing of 100% cotton Ne 30/1 single jersey (190 g/m2) fabric with reactive dyes having azo chromophore group under laboratory conditions, the dyeings made with recovery water with Profoks system were similar to those dyed with osmosis water in terms of color, levelness and fastness performance.

Linear and NLO Properties of Functional Group and Position Isomers of Azo and Azomethine: Comparative Photophysical‐Electrochemical Properties, Z‐Scan and DFT Studies

AbstractFunctional group and position isomers of azo and azomethine were selected to investigate their effect on linear and NLO properties. The azo and azomethine analogs show absorption maxima in the range 460–500 nm and 375–435 nm respectively. They are emissive in green, orange to the deep red region with a large Stokes shift of 100–200 nm. When we compared azo and azomethine chromophores i. e. functional group isomers, azo chromophore shows a bathochromic shift of 50–103 nm, while in case of position isomers azo and azomethine having larger conjugation effect i. e. VA‐2 and VI‐2 show a more bathochromic shift of 28 nm and 42 nm than the corresponding analogs VA‐1 and VI‐1, which show respectively 466 nm and 379 nm. Band gaps evaluated by electrochemical method and DFT method are correlated with the bathochromic shift in absorption maxima. The dyes are thermally stable (up to 280 °C). Open and closed aperture Z‐scan techniques were used to evaluate the third order non‐linear optical (NLO) parameters ‐ nonlinear absorptive coefficient (β), nonlinear refractive index (η2), and third order non‐linear optical susceptibility (χ (3)). NLO properties were theoretically calculated by using DFT method with six different functionals. Mean absolute error (MAE) and standard deviation (SD) were evaluated to get more insight into theoretical calculation. With the set of calculated data points, MAE and SD calculated to check performance of the DFT functional. Different functionals were used to evaluate vertical excitation values and compared it with experimental absorption maxima.

Adsorption and photocatalytic activity of Cu-doped cellulose nanofibers/nano-titanium dioxide for different types of dyes.

Cu-doped cellulose nanofibers/nano-titanium dioxide (Cu-TOCN/TiO2) photocatalysts were prepared by the hydrolysis-precipitation method using TiCl4 as the source of titanium and cellulose nanofibers suspension as a reaction medium. The prepared photocatalysts were used to decolorize organic dyes (reactive brilliant red K-2BP and cationic red X-GRL) efficiently under the synergistic effect of simultaneous adsorption and photocatalysis. The combination of TOCN inhibited the growth of TiO2 crystals, reduced agglomeration and increased the specific surface area. When compared with TiO2, TOCN/TiO2 improved the decolorization efficiency of the two dyes by 14.82% and 22.87%, respectively, under UV-light irradiation. The absorption edge exhibited red-shift from 380 to 410 nm after Cu doping. An excellent photocatalytic activity was recorded by 0.5 mol % Cu-TOCN/TiO2 and the decolorization efficiency of the two dyes was further improved by 34.76% and 10.44% respectively, compared with no Cu doping. After 2 hours of irradiation, the decolorization efficiency reached 96.57% and 99.73% respectively, while under dark conditions, it was 47.64% and 91.56% for the two dyes. The degradation mechanism of the dyes was verified as the destruction of the azo chromophore and benzene ring. This work provides a potential method for the development of a novel adsorptive photocatalyst with excellent recyclability.

Metathesis Cyclopolymerization Triggered Self-Assembly of Azobenzene-Containing Nanostructure.

Azobenzene (AB) units were successfully introduced into poly(1,6-heptadiyne)s in order to ensure smooth synthesis of double- and single-stranded poly(1,6-heptadiyne)s (P1 and P2) and simultaneously realize the self-assembly by Grubbs-III catalyst-mediated metathesis cyclopolymerization (CP) of AB-functionalized bis(1,6-heptadiyne) and 1,6-heptadiyne monomers (M1 and M2). Monomers and polymers were characterized by 1H NMR, mass spectroscopy, and GPC techniques. The double-stranded poly(1,6-heptadiyne)s exhibited a large scale of ordered ladder nanostructure. This result was attributed to the π−π attractions between end groups along the longitudinal axis of the polymers and van der Waals interactions between the neighboring polymeric backbones. While the Azo chromophore connected in the side chain of P2 induced conformation of micelles nanostructure during the CP process without any post-treatment. Furthermore, the photoisomerization of Azo units had an obviously different regulatory effect on the conjugated degree of the polymer backbone, especially for the single-stranded P2, which was attributed to the structural differences and the interaction between AB chromophores in the polymers.

Indole based push-pull dyes bearing azo and dimethine: Synthesis, spectroscopic, NLO, anion affinity properties and thermal characterization

A series of novel indole based push-pull dyes bearing azo and dimethine chromophores in same structure were synthesized and characterized by Fourier Transform Infrared (FT-IR), 1H/13C nuclear magnetic resonance (NMR), and mass spectrometry. The photophysical properties of the dyes were determined in three solvents in UV–vis and theoretical studies. Their chemosensor and nonlinear optic (NLO) properties were also investigated. Anion selectivity and sensitivities of dyes were studied with some selected anions in ACN and interaction mechanisms were confirmed by spectrophotometric and 1H NMR titration techniques. While the dyes showed affinity to F−, AcO−, CN−, and H2PO4− in the organic solvents such as DMSO and ACN and they showed selective behaviour only to CN- in partial aqueous solution. The thermal stabilities obtaining with thermogravimetric analysis (TGA) showed that the dyes have a good thermal stability up to around 300 °C.