Computational modelling of the influence of substituent effects on phthalimidylazo disperse dye hydrolysis and interaction energy

Six azo dyes have been synthesised using N‐substituted phthalimides as diazo components. Substitution effects on dye hydrolysis and intermolecular interactions were investigated with density functional theory (DFT) at B3LYP/6‐311G level. The results showed that the phthalimide moieties adopted a coplanar conformation in respect of the azo‐coupled phenyl rings in all six dyes. N‐Alkyl substitution had little influence on the absorption maxima. Bromo and cyano substitution on the phthalimide ring resulted in hypsochromic and bathochromic shifts of the absorption maxima respectively. Hydrolysis of the phthalimide ring was found to be largely influenced by steric effects rather than inductive effects of substituents. It was also found that π‐stacking interactions of phthalimide/phenyl and phthalimide/phthalimide dimers were promoted by substituents. The results indicated that interactions are dominated by electrostatic and even more importantly dispersion forces. The computational results were also confirmed experimentally.     

Experimental and theoretical insight into the electronic properties of 4-aryl-5-arylazo-3-cyano-6-hydroxy-2-pyridone dyes

In this paper, spectroscopic and quantum mechanical investigation of nine 4-aryl-5-arylazo-3-cyano-6-hydroxy-2-pyridone dyes was performed, and obtained density functional theory (DFT) results were compared with experimental data. The structural and spectroscopic properties of azo-2-pyridone dyes were studied by DFT using B3LYP, CAM-B3LYP, and M06-2X methods with a 6-311++G(d,p) basis set. Comparison of results reveals that the scaled theoretical vibrational frequencies of azo dyes are in good agreement with experimental data. The time-dependent DFT calculated and experimental ultraviolet-visible (UV-vis) absorption spectra are also in good agreement. The effect of electron-donating –OCH₃ and electron-withdrawing –NO₂ groups on the structural parameters, vibrational frequencies, UV-vis absorption, and natural bond orbital (NBO) atomic charges were thoroughly analysed. Vibrational, UV-vis, and NBO analyses confirm that investigated dyes exist in the hydrazo tautomeric form in the solid state and ethanol solution. These analyses signify the occurrence of intramolecular charge transfer in these azo-pyridone dyes.     

Solubilisation of dyes by surfactant micelles. Part 1; Molecular interactions of azo dyes with nonionic and anionic surfactants

An ultraviolet-visible spectroscopic investigation has been made of the interactions of a specially synthesised series of substituted, model arylazonaphthol dyes with nonionic and anionic surfactants. Changes in spectral features were recorded above the critical micelle concentrations, suggesting specific interactions of dyes with micelles of the respective surfactants. The affinity of the dye for the surfactant micelles increased when various p -substituent were incorporated in to the dyes. Similarly, there was a shift in azo–hydrazone tautomeric equilibria and an increase in measured dye p K _a values. Models are proposed for the location of dyes in nonionic or anionic micelles. Unlike earlier studies, it is concluded that the solubilised dye experiences only one environment in nonionic micelles but the specific location, i.e. whether preferentially incorporated in the hydrophobic micellar interior or in the more hydrophilic, outer polyoxyethylene layer, depends upon the nature of the substituent.     

Influence of fluorine-containing substituents on the energy of intermolecular interactions and the heat of evaporation of disperse azo dyes

The heats of evaporation of some fluorine-containing disperse azo dyes have been determined by electronic absorption spectroscopy. The introduction of fluorine or fluorine-containing substituents into azo dye molecules decreases the energy of intermolecular interactions and correspondingly the heat of evaporation of dyes by 10–40 kJ mol^?1 as compared with dyes without fluorine. Such dyes may therefore be recommended for gas-phase methods of dyeing and printing. The energy of orientation-induction interactions is the main contribution to the heat of evaporation.     

Strategies and investigations on bridging squaraine dye units

Synthetic strategies and basic molecular principles were investigated in order to achieve chromophores absorbing light in the far red or even near infrared region. Therefore, a comprehensive series of new squaraine dyes were synthesized and characterized. Beside monomeric unsymmetrical and symmetrical squaraine dyes, also squaraine dye dimers and oligomers bridged with phenylene, fluorene, iso-octyloxy phenylene and tetrafluoro phenylene moieties or directly coupled via condensation reaction were obtained. The influence of the various molecular dye structures to their absorption properties was studied with UV–vis measurements supported by theoretical investigations applying Kiprianov's theory of coupled dyes. With regard to Meyer's theory of the limiting values, the effective number of repeating units for dye series for the highest possible absorption maximum was determined. Observed trends and limiting values for electrochemical potentials and electrical band gaps of the dyes are in agreement with the UV–vis investigations. Finally, calculated molecular structures and frontier orbitals of dimers verify the results of the optophysical and electrochemical studies.     

Characteristic features of the matrix effect on the stokes shift of fluorescent dye molecules in pure and plasticized polymers

The influence of the chemical structure, composition, and physical properties of polymers [polyacrylates and -methacrylates, poly(vinyl acetate), polystyrene, and polybutadiene] and plasticized polymers [poly(methyl methacrylate) and polystyrene] on the Stokes shift of fluorescent dyes has been investigated. The results indicate that the structure and overall mobility of the polymer matrix as well as the nature of the dopant all together influence the separation of the absorption and emission band of a given fluorescent dye. In general, polar and highly flexible polymers favor the band separation. The effect of both polar and apolar dopants seems to be primarily a plasticization in case of polar polymers, whereas for apolar polymers the plasticizer effect can be neglected and the increased Stokes shift upon addition of polar dopants has to be attributed to particular dopant/dye interactions. These findings open some new routes to improve the efficiency of solar collectors based on fluorescent dyes.     

Developing chromic dyeable PET nanocomposites: The dye absorption and complex formation mechanisms

This research aimed to investigate the possibility of enhancement of polyethylene terephthalate (PET) dyeability using nanotechnology. Different kinds of disperse, acidic, and chromic dyes were used for dyeing of produced PET/silver nanocomposite fine multifilament yarns produced at the take up speeds of 3000 m min⁻¹ and their prepared fabrics. Dyeability improved by using acidic dyes. However, the more promotion effect was achieved by chromic dyes. No effect on absorption of disperse dyes revealed that no physical effect can be considered for dye absorption. The electrostatic interaction between silver and acidic dye molecules and forming the coordinative bonds with chromic dye molecules on nanocomposite yarns and fabrics were concluded and thoroughly discussed. Applying chromic dye with the more potential of creating coordinative bonds intensified the improvement of dyeability. Optimized silver ratio for the dyeability enhancement was affected by the mechanisms of dye absorptions discussed and proven by investigating dye concentrations in the effluent baths after the dyeing processes. It has been found that the steric hindrance is the key factor for absorption of chromic dyes; however, it is different in the case of acidic dyes, well discussed according to the dye absorptions mechanisms. The results can be also considered as evidence to prove forming the coordinative bonds with chromic dye molecules. This has also been confirmed by appearing a bathochromic shift in the absorption peaks by increasing dyeability using chromic dye. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

VIS absorption spectrophotometry of disperse dyes

In the investigations of the dyeing processes, the low solubility of disperse dyes in water represents a practical problem for the determination of dye concentration in dyebaths and waste waters. Therefore the use of an organic solvent which, dissolves disperse dyes, is recommended in visible spectrophotometry of disperse dyes. Three organic solvents (ethanol, N,N-dimethylformamide, acetone) and two disperse dyes, the disazo dye C.I. Disperse Orange 29 and the anthraquinone dye C.I. Disperse Blue 56, were used for spectroscopic analysis in this present work. The absorbance of aqueous dye dispersions and various organic solvent dye solutions was measured to evaluate the effect of the solvent on the shape and intensity of the absorption spectra and on the wavelength shift of maximum absorption. The validity of Beer–Lambert’s law in each system was ascertained. A suggestion is made how VIS absorption spectrophotometry can be used to determine the dye concentration in disperse dyebaths. The addition of organic solvent to the dyebath leads to dye dissolution, and the Beer-Lambert’s law is then fulfilled. The optimum ratio between the dyebath dispersion and the organic solvents for the dyes investigated is also determined.     

Understanding the Electronic Structures and Absorption Properties of Porphyrin Sensitizers YD2 and YD2-o-C8 for Dye-Sensitized Solar Cells

The electronic structures and excitation properties of dye sensitizers determine the photon-to-current conversion efficiency of dye sensitized solar cells (DSSCs). In order to understand the different performance of porphyrin dye sensitizers YD2 and YD2-o-C8 in DSSC, their geometries and electronic structures have been studied using density functional theory (DFT), and the electronic absorption properties have been investigated via time-dependent DFT (TDDFT) with polarizable continuum model for solvent effects. The geometrical parameters indicate that YD2 and YD2-o-C8 have similar conjugate length and charge transfer (CT) distance. According to the experimental spectra, the HSE06 functional in TDDFT is the most suitable functional for describing the Q and B absorption bands of porphyrins. The transition configurations and molecular orbital analysis suggest that the diarylamino groups are major chromophores for effective CT excitations (ECTE), and therefore act as electron donor in photon-induced electron injection in DSSCs. The analysis of excited states properties and the free energy changes for electron injection support that the better performance of YD2-o-C8 in DSSCs result from the more excited states with ECTE character and the larger absolute value of free energy change for electron injection.     

Dye aggregation and interaction of dyes with a water‐soluble polymer in ink‐jet ink for textiles

Detailed understanding of the interaction between dyes and additives and the aggregation behaviour of the dye molecules in aqueous solutions is required to develop ink‐jet ink for textiles. In the present study, the aggregation behaviour of three acid dyes (CI Acid Red 88, CI Acid Red 13 and CI Acid Red 27) containing different number of sulphonate groups in aqueous solutions was investigated by means of visible absorption spectroscopy. As a result, the higher the solubility of the dyes in water (the larger the number of sulphonate groups in the dyes), the lower are the aggregation constants of the dyes. For all the dyes, the aggregation constants decreased with increasing temperature, indicating the exothermic process of the dye aggregation. The thermodynamic process for CI Acid Red 88 with one sulphonate group is less enthalpic and more entropic than that for CI Acid Red 13, which contains two sulphonate groups. CI Acid Red 27, which includes three sulphonate groups, hardly forms any aggregates. To elucidate the effects of the polymer additive, the binding constants of the dyes with the water‐soluble polymer, poly(vinylpyrrolidone) and the aggregation constants of the dyes in aqueous polymer solutions were also estimated. In addition, the binding constants were influenced by the number of sulphonate groups in the acid dyes: the larger number of sulphonate groups diminished the binding constants. The aggregation constants in the presence of poly(vinylpyrrolidone) were smaller than those in its absence at every temperature for all dyes. This suggests that poly(vinylpyrrolidone) has disaggregation effects. Furthermore, poly(vinylpyrrolidone) makes the aggregation process less enthalpic with a greater entropic change. Thus, the aggregation process of the dyes in the polymer solutions is thermodynamically different from that in water, reflecting the interactions between the dyes and the polymer.     

Photophysical properties of coumarin derivatives incorporated in MCM-41

Highly ordered MCM-41 has been synthesized and four coumarin derivative dyes were incorporated into it by impregnation method. The absorption and emission spectra of four coumarin derivatives in both toluene and MCM-41 were examined to explore the structural and environmental effects on the optical properties of these dyes. The spectra results indicated that dye molecules existed in monomer form within MCM-41. The maxima of absorption and emissions shifted to red compared with those in toluene due to the strong host–guest interactions. The shifts of emission maxima increased with increasing the volume of the dyes.     

Some Observations on the Effect of Urea on the Dyeing Behaviour of Wool at Low Temperatures

The effect of adding urea to the dyebath on the rate of absorption of reactive and acid dyes by wool, and of acid dyes by other protein bres, has been studied. Possible modesof action of aqueous solutions of urea on wool are discussed. The observed increase in the ite of dyeing in the presence of urea is due to disaggregation of the dye in solution and reduction in dye-protein hydrophobic interactions. The action of urea in promoting fibre swelling is also likely to be a contributory factor.     

Dichroic and spectral properties of anthraquinone-based azo dyes for PVA polarizing film

Dichroic dyes with broad absorption bands are advantageous for the production of neutral gray polarizing films. For this purpose, anthraquinone-based azo dyes were synthesized to have a conjugated bichromophore design and this was applied to PVA polarizing films. The spectral and dichroic properties of the polarizing films were examined and compared to the films produced with a general disazo dichroic dye. The polarizing films with anthraquinone-based azo dyes had wider absorption bands, but lower dichroic ratios compared to the films with a general disazo dichroic dye. It was found that the alignment between the transition moments of the anthraquinone and azo chromophores is an important factor for the dichroic properties of anthraquinone-based azo dyes.     

Fluorescence and kubelka-munk theory

An expression is derived for the spectral radiance factor of a thick sample of material which scatters and absorbs light, and to which has been added a fluorescent dye. It is also shown how to work backwards, calculating absorption and emission spectra of the dye from measurements on dyed and undyed samples. This theory has practical application in colorant formulation, and examples using up to three dyes to colour paper are discussed.     

两个新的2-萘酮衍生物的合成与光物理性质

以咔唑为电子给体、羰基为电子受体,合成了一个新的D-π-A型有机染料1(1-(2-萘基)-3-(N-乙基咔唑)-丙烯酮)和一个新的以咔唑为电子给体中心的A-π-D-π-AV型双枝有机染料2(3,6-二[1-(2-萘基)丙烯酮]-N-丁基咔唑)。系统研究了它们在不同溶剂和聚合物基质中的光物理性质。研究发现,双枝有机染料2相对于单枝染料1吸收和荧光强度大大增强,在聚合物基质中的荧光强度相对于溶液中大大增强,即使掺杂浓度较高时也没有因生成分子的聚集体而发生明显的荧光猝灭。     

Synthesis of novel oxidizable polymerization sensitizers based on the dithiinoquinoxaline skeleton

Novel dyes, based on the dithiinoquinoxaline skeleton, were synthesized and characterized using ¹H NMR spectroscopy and chemical ionization mass spectroscopy. Their spectral properties, such as absorption, emission spectra and quantum yield of fluorescence, were also measured. Electron donating properties of the title compounds were estimated on the basis of DFT calculations. The studied dyes were used as oxidizable sensitizers for 2,4,6-tris(trichloromethyl)-1,3,5-triazine (Tz). The dye/Tz photoredox pairs were found to be effective visible-wavelength initiators of free radical polymerization. The ability of these systems to act as photoinitiators strongly depended upon the free energy change of the photoinduced electron transfer from the excited dyes to Tz. It has been shown that the intermolecular electron transfer is the limiting step in the photopolymerization initiated by these studied initiator systems.     

The solubility parameter concept applied to disperse dyeing of polymers

The solubility parameter concept offers a logical link between the theory of solutions and of nonionic (disperse) dyeing. An attempt has been made to apply the concept to correlate the solubility of several disperse dyes in secondary cellulose acetate, cellulose triacetate, and polypropylene with the calculated solubility parameters of both the polymers and the dyes. When the dyes are applied on hydrophilic polymers from an aqueous dispersion, the correlation between the solubility parameter concept and the dye solubility is not close. One of the reasons for this may be the fact that dyeing of the fibers is, in fact, not a solution in the dry fibers, but consists essentially either in displacement of water molecules from the water swollen fibers and/or, perhaps, in additional swelling by the dye. Consideration of this fact and also correcting for the contribution of hydrogen bonding and dipole interactions to the cohesive energy density brings the disperse dye solubility data into a better agreement with the concept. The concept should be applicable without complications to the dyeing of nonpreswollen fibers, such as polypropylene from aqueous dispersion, or any fiber by the Thermosol process and particularly to dyeing from the vapor phase. The few data available appear to support this view.     

Decolorisation of reactive dye wastewater and the effect of surfactants using laccase

Laccase (benzenediol, oxidoreducase; Enzyme Commission Number) is a multi‐copper oxidase from biomass. Laccase enzyme recycling on molecular oxygen as an electron acceptor can be applied for the decolorisation of synthetic dyes. The decolorisation of 49 commercial reactive dyes using laccase was investigated. The effects of diverse structure surfactants on decolorisation are discussed. The absorption spectra of reactive dyes after a laccase biodegradable reaction were analysed. Reactive dyes based on anthraquinone and azo structures could be decolorised using the enzyme and their chemical structures broken. Reactive dyes based on an anthraquinone structure were easier to decolorise than those based on an azo structure. Surfactants could affect the decolorisation of dyes with an enzyme. The effect of nonionic surfactant on the decolorisation of anthraquinone dyes was the reverse. The cationic surfactant could improve the decolorisation rate of diazo dye. The effect of the anionic surfactant on dye decolorisation was small. Most commercial reactive dyes could be decolorised and biodegraded using a laccase enzyme under mild conditions. Laccase enzyme biotechnology has potential applications in the decolorisation of reactive dye wastewater.     

Dye–fiber interactions in PET fibers: Hydrogen bonding studied by IR‐spectroscopy

Dye–fiber interactions are studied in poly (ethylene terephthalate) fibers by FT‐IR spectroscopy. It is shown for the first time that DRIFTS (diffuse reflectance infrared Fourier transform spectroscopy) serves as an easy applicable and accurate technique for the study of fibrous structures. This article focuses on the possible hydrogen bond interactions in the dye–fiber system, where the PET fibers are dyed with anthraquinone‐based disperse dyes. The dyes and related anthraquinone structures are studied in both the dilute solution state, the solid state, and as present in the PET fibers. It is proven that 1‐amino anthraquinones show strong “chelate‐type” intramolecular hydrogen bonding in all three states. In the fibers an important supplementary intermolecular hydrogen bonding with the C?O groups in the PET fiber is observed. The extend of hydrogen bonding seems to be prone to dye concentration variations. Further analysis by modulated differential scanning calorimetry links the hydrogen bonding to an intrinsic plasticizing effect of the dyes affecting the dye diffusion process. This thus offers a tool for the fundamental understanding of the dyeing process and possible observed differences in dyeing behavior in dye–fiber systems. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

New insights into dye chemistry and physics

A review of the academic dye research performed by the Port Sunlight group and its coworkers over the past 15 years is presented. The work is focused on three areas: (1) substrate structure; (2) dye interactions in aqueous solution and on substrates; (3) dye degradation and products. For substrates, a detailed model of the nanoenvironment experienced by chemicals within cellulose fibre is given, showing the different environments and remarkable mobility of absorbed chemicals. Advanced nuclear magnetic resonance diffusion measurements provide the complex pathways by which compounds find their way in and out of the fibre. For dye interaction, detailed theoretical and experimental studies are reported on three model dye systems, the anionic monoazo dye Orange II, the bisazo anionic dye CI Direct Blue 1, and cationic monoazo thiazolium dyes, providing a comprehensive picture of their structure. A quantitative mechanism of dye binding to cellulose is shown. Resonance Raman provides an effective forensic tool for dye identification, even from single fibres. The products and kinetics of Orange II dye degradation by one‐electron reduction in aqueous solution is given, with the identification of an indophenol dye end‐product. In cellulosic materials the reduction mechanism is similar to solution, when the higher microviscosity is accounted for. Hydrolysis of thiazolium dyes occurs at both aromatic rings of the dye but on different timescales. Measurement and calculations of the electronic structures of one‐electron‐reduced and ‐oxidised dyes are presented. The mechanism of photooxidation by sunlight of azo dyes in cotton is delineated.