Colorants doi: 10.3390/colorants3020006
Authors: Bence Kontra Zoltán Mucsi László Vanyorek Miklós Nagy
Smart solvatochromic isocyano-aminoarenes (ICAArs) have been gaining attention owing to their unique photophysical, antifungal and anticancer properties. Using a simple dehydration reaction with in situ-generated dichlorocarbene, we prepared 2-amino-7-isocyanofluorene (2,7-ICAF). We studied the effect of the longer polarization axis provided by the fluorene core on the spectral properties and we also compared it to those of the starting diamine. 2,7-ICAF shows a clear solvatochromic behavior close to the blue part (370–420 nm) of the visible spectrum. Quantum chemical calculations show internal charge transfer (ICT) between the donor amino and the electron-withdrawing isocyano groups. 2,7-ICAF has high molar absorptivity (ε = 15–18·103 M−1cm−1) and excellent quantum yield (Φf = 70–95%) in most solvents; however, its fluorescence is completely quenched in water. The high brightness (ε·Φf) and close to zero quantum yield in water may be favorable in biolabeling applications, where background fluorescence should be kept minimal. Overall, 2,7-ICAF shows enhanced photophysical properties compared to its previously investigated relative 4-amino-4′-isocyano-1,1′-biphenyl (4,4′-ICAB).
]]>Colorants doi: 10.3390/colorants3010005
Authors: Kelly Rodrigues Alana M. X. de Sousa Andreza D. O. dos Santos Bárbara C. A. Barbosa A. Rita Silva Luciana Pereira Glória M. M. Silva
Effluents from the textile industry are an active problem in the sector and one of the world’s main environmental problems. The conventional treatments applied are not always efficient in terms of compliance with legislation, and, in many cases, the efficiency of treatment is guaranteed by the enormous energy expenditure involved, camouflaging the momentary problem and not effectively treating it. In this work, batch reactors with immobilized biomass of Aspergillus niger AN400 were arranged in series for the treatment of real textile wastewater containing approximately 20 mg/L of indigo carmine. Sucrose was added as a co-substrate in concentrations of 1 g/L and 0.5 g/L, in the first and second reactors, respectively, over 19 cycles of 48 h. The highest decolorization rate in the system was (93 ± 4) %, with the largest amount removed in the first reactor (90 ± 6) %, occurring mainly by biological means. The production of aromatic by-products from the initial degradation of the dye molecule was reflected in the lower removal efficiency of dissolved organic matter: 52% in the first reactor, and 25% in the second reactor. The number of colonies of fungi was higher than that of bacteria, 2.24:1 and 2.44:1 in the first and second reactors, respectively. The treated effluent in the system showed less toxicity than the raw effluent, and this demonstrates the potential of this technology in the treatment of textile effluents containing indigo carmine.
]]>Colorants doi: 10.3390/colorants3010004
Authors: Estelle Leonard China Takeda Takashiro Akitsu
Azo-Schiff bases contain an azo photochrome showing isomerization accompanying with color change, and an imine moiety (which can contribute to the metal complexation capability). The syntheses of these molecules will be described, and their dyes applications will be discussed, such as for fuel cells, as photometric or colorimetric sensors. In addition, liquid crystals and their antibacterial efficiencies will also be discussed.
]]>Colorants doi: 10.3390/colorants3010003
Authors: Ana N. Nunes Joana Monte Soraya Rodríguez-Rojo Isabel D. Nogueira Luís F. Gouveia Carla Brazinha Ana A. Matias
Dunaliella salina has been recognized as an excellent biomass source of carotenoid, which can be used as a natural orange coloring agent for food products. The most eco-friendly approach for extracting carotenoid is through supercritical carbon dioxide extraction, as it yields highly concentrated extracts while preventing pigment thermal degradation. However, there are limitations when a lipophilic extract is considered a food ingredient, in particular very difficult handling and low solubility in water-based products. The aim of this study was to develop a hydrosoluble form of a natural carotenoid-rich extract recovered from algae biomass within a biorefinery concept to be incorporated in aqueous-based food products. A two-step process was developed, starting with the emulsification of the supercritical extract into a mixture of maltodextrin and gum arabic, using soy lecithin as an emulsifier. The emulsification was followed by a spray-drying step. The impact of process variables on the encapsulation yield, efficiency, emulsion properties, and particle characteristics was studied. The resulting particles exhibited an intense orange color and good water dispersibility, facilitating uniform yellow coloring when incorporated into an aqueous-based product. Overall, spray-drying emulsions containing carotenoids derived from Dunaliella salina prove to be a promising strategy for the global market demand for natural colorants.
]]>Colorants doi: 10.3390/colorants3010002
Authors: Olga Kirkilessi Christina Arapatzi Heribert Reis Vassiliki Kostourou Kyriakos C. Prousis Theodora Calogeropoulou
A library of seven novel 1,3-benzothiazole-substituted BODIPY derivatives with tunable optical properties was synthesized. The new fluorescent dyes exhibited bathochromically shifted absorptions (up to 670 nm) and emissions centered in the red and near-infrared spectral region (up to 677 nm) in comparison to the parent compound 8-phenyl BODIPY (λabs: 499 nm, λemi: 508 nm). (TD)DFT calculations were performed to rationalize the spectroscopic properties of the new dyes. The cellular biodistribution of the new BODIPY dyes, their fluorescence stability and toxicity were investigated in both living and fixed fibroblasts using time-lapse fluorescent imaging and confocal microscopy. Six of the seven new dyes were photostable and non-toxic in vitro at 10 μM concentration. In addition, they efficiently stained the cell membrane, showing diffuse and dotty localization within the cell at low concentrations (1.0 and 0.1 μM). Specifically, dye TC498 was localized in vesicular structures in both live and fixed cells and could be used as a suitable marker in co-staining studies with other commonly used fluorescent probes.
]]>Colorants doi: 10.3390/colorants3010001
Authors: Lydia R. Milam Roy P. Planalp
Remediation of organic dyes in natural waters is a significant environmental need under active study. This review analyzes bimetallic catalytic degradation systems that are based on the Fenton chemistry concept and that generate reactive oxygen species (ROS) as the agent of dye breakdown. Recently developed advanced oxidation processes (AOPs) take advantage of bimetallic heterogeneous catalysts to facilitate rapid rates and full degradation. Catalysts based on two metals including iron, copper, molybdenum, cobalt and magnesium are discussed mechanistically as examples of effective radical ROS producers. The reactive oxygen species hydroxyl radical, superoxide radical, sulfate radical and singlet oxygen are discussed. System conditions for the best degradation are compared, with implementation techniques mentioned. The outlook for further studies of dye degradation is presented.
]]>Colorants doi: 10.3390/colorants2040036
Authors: Kazuki Yamaguchi Satoru Mochizuki Yudai Nagato Takuro Morimoto Toshiyuki Masui
Y(Mn0.95M0.05)2O5 (M = Al, Fe, Ga, Ti, and Zr) samples were synthesized via a sol–gel method using citric acid to find a new near-infrared (NIR) reflective black pigment. Among these samples, the optical reflectance of Y(Mn0.95Fe0.05)2O5 and Y(Mn0.95Ga0.05)2O5 in the near-infrared region was found to be larger than that of YMn2O5. Then, the concentration of the dopant (Fe or Ga) was changed between 0 and 15%, and the resulting UV–Vis–NIR reflectance spectra were measured. As a result, the optical reflectance of the Fe-doped samples decreased in the near-infrared region, while that of the Ga-doped samples increased. Accordingly, Y(Mn1−xGax)2O5 (0 ≤ x ≤ 0.20) samples were synthesized, and the crystal structure, particle size, optical properties, and color of the samples were characterized. The single-phase samples were obtained in the composition range of 0 ≤ x ≤ 0.15, and the lattice volume decreased with increasing Ga3+ concentration. Optical absorption below 850 nm was attributed to the charge transfer transition between O2p and Mn3d orbitals, and the absorption wavelength of Y(Mn1−xGax)2O5 shifted to the shorter wavelength side as the Ga3+ content increased, because of the decrease in the Mn3+ concentration. Although the sample color became slightly reddish black by the Ga3+ doping, the solar reflectance in the near-infrared region reached 47.6% at the composition of Y(Mn0.85Ga0.15)2O5. Furthermore, this NIR reflectance value was higher than those of the commercially available products (R < 45%).
]]>Colorants doi: 10.3390/colorants2040035
Authors: Jose Manuel Barrera-Andrade Natali de la Fuente-Maldonado Ricardo Lopez-Medina Ana Marisela Maubert-Franco Elizabeth Rojas-Garcia
Due to the high stability of azo-type dyes, conventional treatment processes such as adsorption, flocculation, and activated sludge are not efficient for decolorizing wastewater effluents. An alternative to traditional wastewater treatment is photocatalysis, which has gained significant interest because research has shown it to be a viable and cost-effective process that uses sunlight as an inexhaustible energy source. In heterogeneous photocatalysis, a photocatalyst is required, such as TiO2, ZnO, composite materials, and, more recently, metal–organic frameworks (MOFs). MOFs, also known as “coordination polymers”, exhibit photocatalytic properties and have been proven to be promising materials in the photocatalytic degradation of dyes. This study presents recent advances in using MOFs as photocatalysts to degrade recalcitrant contaminants like azo-type dyes. Recent advancements in developing photocatalysts based on MOFs are focused on two strategies. Firstly, the development of new MOFs composed of complex ligands or a mixed ligand system, and secondly, the synthesis of composite materials based on MOFs and metal oxides, metals, sulfides, nitrides, etc. Both strategies have significantly contributed to the search for new semiconductors to degrade some recalcitrate contaminants in wastewater.
]]>Colorants doi: 10.3390/colorants2040034
Authors: Safalmani Pradhan Yuki Kurokawa Suraya Shaban Shyam S. Pandey
The design and development of sensitizing dyes possessing wide-wavelength photon harvesting encompassing visible to near-infrared (NIR) wavelength regions are unavoidable for increasing the overall efficiency of dye-sensitized solar cells (DSSCs). In this study, three far-red-sensitive squaraine sensitizers were designed computationally, synthesized, and characterized, aiming towards their suitability as a potential sensitizer for DSSCs. It has been found that the incorporation of an electron acceptor moiety in the central squaraine core brought about a red shift in the absorption maximum (λmax) and the emergence of a secondary absorption band in the blue region, thus broadening the photon-harvesting window. In addition, it also lowered the dye’s HOMO energy level enabling a facile regeneration of the photo-excited dye, which improved the photovoltaic performance of SQ-223, exhibiting a photoconversion efficiency (PCE) of 4.67%. Thereafter, to address the issue of wide-wavelength photon harvesting, DSSCs were fabricated by co-adsorbing two complementary dyes SQ-223 and D-131 in various molar ratios. The DSSC fabricated with D-131 and SQ-223 in 9:1 molar ratio displayed the best photovoltaic performance with a PCE of 5.81%, a significantly higher PCE when compared to corresponding individual dye-based DSSCs containing D-131 (3.94%) and SQ-223 (4.67%).
]]>Colorants doi: 10.3390/colorants2040033
Authors: Abigail Trujillo-Vazquez Fereshteh Abedini Alina Pranovich Carinna Parraman Susanne Klein
Two of the most significant cases of extant 16th-century featherwork from Mexico are the so-called Moctezuma’s headdress and the Ahuizotl shield. While the feathers used in these artworks exhibit lightfast colors, their assembly comprises mainly organic materials, which makes them extremely fragile. Printed media, including books, catalogs, educational materials, and fine copies, offer an accessible means for audiences to document and disseminate visual aspects of delicate cultural artifacts without risking their integrity. Nevertheless, the singular brightness and iridescent colors of feathers are difficult to communicate to the viewer in printed reproductions when traditional pigments are used. This research explores the use of effect pigments (multilayered reflective structures) and improved halftoning techniques for additive printing, with the objective of enhancing the reproduction of featherwork by capturing its changing color and improving texture representation via a screen printing process. The reproduced images of featherwork exhibit significant perceptual resemblances to the originals, primarily owing to the shared presence of structural coloration. We applied structure-aware halftoning to better represent the textural qualities of feathers without compromising the performance of effect pigments in the screen printing method. Our prints show angle-dependent color, although their gamut is reduced. The novelty of this work lies in the refinement of techniques for printing full-color images by additive printing, which can enhance the 2D representation of the appearance of culturally significant artifacts.
]]>Colorants doi: 10.3390/colorants2040032
Authors: Leonardo Ricardo Bernardes da Conceição Higor Oliveira da Cunha Arcano Matheus Bragança Leite Rajendran Suresh Babu Sebastian Raja Caue Ribeiro Ana Lucia Ferreira de Barros
Herein, we evaluate the conversion efficiency of dye-sensitized solar cells (DSSCs) photosensitized using two different natural dyes extracted from Alpinia purpurata and Alstroemeria flower petals. The appreciable absorption capacity of the extracts in the visible light region was examined through absorption spectroscopy. The functional groups of the corresponding pigments were identified through Fourier transform spectroscopy (FTIR) technique thus indicating the presence of cyanidin 3-glycosides and piperine in the flowers of Alstroemeria and Alpinia purpurata. The extracted dyes were immobilized on TiO2 on transparent conducting FTO glass, which were used as photoanode. The dye-coated TiO2 photoanode, pt photocathode and iodide/triiodide redox electrolyte assembled into a cell module was illuminated by a light source intensity 100 mW/cm2 to measure the photovoltaic conversion efficiency of DSSCs. The TiO2 anode and Pt counter electrode surface roughness and morphological studies were evaluated using atomic force microscope (AFM) and field emission scanning electron microscopy (FESEM), respectively. Through the photoelectric characterizations, it was promising to verify that the solar conversion efficiency was calculated with the photovoltaic cell sensitized by Alstroemeria and Alpinia purpurata. This was achieved with a yield (η) of 1.74% and 0.65%, with an open-circuit voltage (Voc) of 0.39 and 0.53 V, short-circuit current density (Jsc) of 2.04 and 0.49 mA/cm2, fill factor (FF) of 0.35 and 0.40, and Pmax of 0.280 and 0.100 mW/cm2, respectively. The results are promising and demonstrate the importance of the search for new natural dyes to be used in organic solar cells for the development of devices that generate electricity in a sustainable way.
]]>Colorants doi: 10.3390/colorants2040031
Authors: Leonel C. Silva Vanessa Otero Maria J. Melo Eurico J. Cabrita Luís Mafra
This work provides significant insight into the molecular structure of alizarin lake pigments used by artists in the past. To characterize two red powders, lakes 1 and 2, obtained by complexation of 1,2-dihydroxy anthraquinone (alizarin) with Al3+, a multi-analytical approach was designed based on solid and liquid state Nuclear Magnetic Resonance Spectroscopy (NMR), Fourier-Transform Infrared Spectroscopy (FTIR), Mass Spectrometry (MS) and Density Functional Theory (DFT) calculations. Lake 1 was synthesized according to literature and compared with lake 2, a reproduction of an artist’s pigment. FTIR showed Al3+ coordinated to oxygens in C1 and C9, and that in lake 2 the -OH groups in C2 are protonated, being responsible for its low solubility. 1H-NMR proved that lake 2 is formed by two tautomers [Al(Aliz-2-H-)2(OH)(H2O)] and [Al(Aliz-10-H-)2(OH)(H2O)], the latter being the major species. SS-NMR was the only technique that got insight into the Al3+ coordination, octahedral for both lakes. It confirmed the existence of two species in lake 2, in a 5:1 ratio. Both are amorphous “open structures”, resulting in fewer constraints for the ligands and in a large variety of geometries. SS-NMR allowed the analysis of the red pigments without preparation, which is a unique advantage for their study in artworks.
]]>Colorants doi: 10.3390/colorants2040030
Authors: Almudena Martí Pau Arroyo Pablo Gaviña Salvador Gil Margarita Parra José A. Sáez
Derived from malachite green, new triaryl-carbonium-ion-functionalized gold nanoparticles have been synthesized for detecting anions. The detection process, and concomitant colour change, is based on charge compensation on the surface of nanoparticles, which triggers their aggregation, resulting in a bathochromic shift of the plasmon resonance band. The difference in electrophilicity of the malachite green triaryl ions in solution or on gold nanoparticles makes it possible to distinguish different anions related to their nucleophilic character.
]]>Colorants doi: 10.3390/colorants2030029
Authors: Luca M. Sihn Erick L. Bastos Marcelo Nakamura Mayara K. Uchiyama Henrique E. Toma
Blue dyes are relatively uncommon in nature, and a novel dithiophene dye (RanB) is reported in this paper. This dye is derived from an old anti-osteoporotic drug and is a metal ion complexing agent, displaying a planar molecular structure, with two sets of carboxylate, isonitrile, thiophene, and iminodiacetate groups. The blue color originates from a strong absorption peak at 648 nm, accompanied by an unusual fluorescence at 555 nm, with higher energy compared to the main absorption band. RanB forms complexes with lanthanoid ions through the iminodiacetate groups and serves as an effective sensitizer for Tb3+ ions, heightening their emission and improving their use as luminescent agents. Its photo-physical properties and the interaction with Tb3+ have been investigated using absorption spectroscopy, steady-state and time-resolved fluorescence spectroscopy, along with computational methods (ZINDO/S and DFT). The RanB toxicity in human umbilical vein endothelial cells has also been tested, showing a lack of toxicity, holding promising prospects for application as a luminescent and coloring agent in pharmaceuticals and food.
]]>Colorants doi: 10.3390/colorants2030028
Authors: Daiane Amaral de Ramos Nogueira Tânia Marina Palhano Zanela Monielly Viomar Machado Carlos Alberto Policiano Almeida Rafael Marangoni
Zinc hydroxide nitrate (ZHN) was used as an anionic adsorbent for the removal of methyl orange (MO) dye from aqueous solutions. ZHN was characterized via X-ray diffraction (XRD) and infrared spectroscopy (FTIR) techniques. Investigations were carried out to see how the adsorption of MO was affected by factors such as initial MO concentration, contact time and temperature. Adsorption isotherms were analyzed using the Langmuir and Freundlich equations, with the first one being the better result for the equilibrium data. Adsorption kinetics was studied through applying pseudo-first and pseudo-second-order kinetic models, and the experimental data were better fitted to the pseudo-second-order model. The activation energy was determined using the Arrhenius equation to be 105.45 kJ mol−1, revealing the chemical nature of the adsorption process. The thermodynamic parameters were also determined, showing the adsorption of MO onto ZHN to be a non-spontaneous and exothermic process. The experimental results showed ZHN as a potential adsorbent with adsorption capacity for removing anionic dyes from water medium.
]]>Colorants doi: 10.3390/colorants2030027
Authors: Masanari Namie Jae-Ho Kim Susumu Yonezawa
Surface fluorination with pure F2 gas can easily make the surface on PP (polypropylene) hydrophobic, and it causes limited dyeability, as reported in a previous paper. In this study, to produce a more hydrophilic surface, surface fluorination of PP was performed at 25 °C, total gas pressure of 13.3 kPa, and reaction time of 1 h using F2 and O2 mixtures with different proportions of F2 gas. The surface roughness of the fluorinated PP samples was about 1.5 times higher than that of the untreated sample (5 nm). Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy (XPS) results showed that the PP-derived bonds (-C-C- and -CHx) decreased because they were converted into polar groups (-C–O, -CHF-, and -CFx), which increased the surface electronegativity of the PP. The variation in the F2 gas proportion in the gas mixture significantly affected the hydrophilicity and surface composition of the PP. At F2 gas proportions of <70%, the hydrophilicity of the fluorinated PP samples was increased. Notably, the hydrophilic and negatively charged PP surface enhanced the dyeing of the polymer with basic methylene blue (MB). In contrast, at F2 gas proportions of >90%, the PP surface became hydrophobic owing to increased numbers of hydrophobic -CF3 bonds. Thus, enhanced PP dyeing can be controlled based on the composition of the F2 and O2 gas mixture.
]]>Colorants doi: 10.3390/colorants2030026
Authors: Eleonora Balliana Eugénie Marie Claudine Caveri Laura Falchi Elisabetta Zendri
The 18th century roof tiles from the “Casa delle vigne”, located in the Aosta region (north-east Italy), were investigated as an example of a peculiar historical roof covering: ceramic tiles with a lead-based glaze finishing to waterproof them are used to create colourful patterns. A conservation project proposed the integration of the original tiles with new ones, produced according to traditional methods. Ancient and new tiles were analysed with Fiber Optics Reflectance Spectroscopy, micro-Raman, Fourier Transform Infrared Spectroscopy and X-ray Fluorescence Spectrometry, Thermogravimetry and Differential Scanning Calorimetry for understanding the composition and the production technology of this manufacture. Their resistance to freezing and thawing cycles was then tested, considering their exposure in the severe alpine climate of Aosta. The use of pure clays with low calcium contents, high firing temperature and lead-rich glazes was found in ancient tiles, able to outstand several freezing-thawing cycles without damages. Iron and copper pigments were used in old yellow and green glazes. Zinc-based pigment, low lead and calcium-rich glazes are used in the new ones, which remained mainly coherent to the ceramic body during the freeze-thaw test.
]]>Colorants doi: 10.3390/colorants2030025
Authors: Eva Miguel Guillermo Paulo-Redondo Juan Bautista Carda Castelló Isaac Nebot-Díaz
In this study, a new red ceramic pigment has been developed within a perovskite structure, and microwave heat treatments have been applied. Those red ceramic pigments within the YAlO3 system doped with chromium with the nominal composition Y0.98Al0.98Cr0.04O3 were synthesized by traditional routes and alternative methods like coprecipitation. Also, heat treatment has been studied comparing a traditional electric and microwave kiln. Different flux agents have been incorporated to improve the synthesis reaction. Prepared pigments have been characterized by X-ray diffraction (XRD) as having a predominant phase of perovskite structure, which is responsible for the red shade, and a minority garnet phase that causes more brown colorations. Studies by Ultraviolet-Visible spectroscopy gave rise to a series of absorption bands that indicate the presence of Cr(III) in the octahedral position corresponding to perovskite and Cr(IV) corresponding to garnet in both the octahedral and tetrahedral positions. The perovskite phase is favored with the use of flux mix, corroborating the UV-visible results and being more pronounced in traditional high temperature thermal treatments. The coprecipitation route has been studied to increase the reactivity of the particles given their nanometric size; however, this reactivity favors a greater appearance of undesirable garnet phases with both types of flux. Scanning Electron Microscopy (SEM) micrographs offer information obtained from the secondary electrons of predominantly cubic crystalline phases with sizes between 1 µm and 2 µm in pigments synthesized via the traditional method and sizes less than 1µm together with the glassy phase in pigments synthesized via coprecipitation. Microwave thermal treatments have been studied, obtaining pigments with a majority structure of perovskite and garnet at lower temperatures and relatively short synthesis times. The feasibility of use in porous single-fired ceramic glazes has been studied, whose chromatic coordinates have been collected using an Ultraviolet-Visible Spectrophotometer based on the CIEL*a*b* system.
]]>Colorants doi: 10.3390/colorants2030024
Authors: Sergey V. Shekhovtsov Iryna V. Omelchenko Svitlana V. Shishkina Andrey O. Doroshenko Kateryna O. Vus Hanna S. Vlasenko Nikolay O. Mchedlov-Petrossyan
Contrary to the 4′- and 5′-nitro- and aminofluoresceins, the corresponding 3′-derivatives are practically unexplored. In this paper, we describe the synthesis and spectral properties of 3′-nitrofluorescein and 3′-aminofluorescein, as well as their methyl esters. Among other methods, X-ray analysis, 13C NMR spectroscopy, and ESI mass spectrometry made it possible to establish the molecular structure of the target compounds as well as intermediates and by-products. Some unexpected products, though in small amounts, were revealed within the course of study. Whereas the fluorescence of the double-charged R2− ion of 3′-nitrofluorescein in both aqueous and organic solvents is weak, the R2− anion of 3′-aminofluorescein in a non-hydrogen bonding donor solvent, but not in water, exhibits intensive fluorescence, analogous to the case of 4′- and 5′-aminofluoresceins. Interestingly, the λmax values in water of the R2− ions bearing an NO2 group in the 3′- and 6′-positions are 7 to 10 nm higher than those of the 4′- and 5′-nitro derivatives. The difference was also observed in dimethyl sulfoxide. This correlates with the angles between the xanthene and phthalic planes of the dyes. The dye 3′-aminofluorescein could be used as a fluorescent indicator sensitive to hydrogen bonding ability of the solvent. It could also serve as a platform for synthesizing fluorescent molecular probes for biochemical research, analogous to the very popular application of 4′- and 5′-amino derivatives.
]]>Colorants doi: 10.3390/colorants2030023
Authors: Lariana N. B. Almeida Tatiana G. Josué Maria Eduarda K. Fuziki Yuri B. Fávaro Laura S. Ribas Angelo M. Tusset Onélia A. A. Santos Giane G. Lenzi
In the present work, rock dust was evaluated as an adsorbent and heterogeneous photocatalyst in the discoloration of Basazol Yellow 46 L dye, which is widely used in the dyeing of molded pulp packages. Although rock dust is produced in large quantities in quarries as a byproduct of rock exploration, little is known about its application as a photocatalyst. Rock dust was characterized by XRD, SEM/EDS, photoacoustic spectroscopy, and N2 physisorption and had its photocatalytic activity assessed through phenol and salicylic acid degradation tests. The characterization results showed that the rock dust is mainly composed of silica and alumina in a triclinic structure, has a bandgap energy of 2.36 eV, and has a specific area of 1.5 m2/g. Rock dust was proven to be photocatalytically active in phenol and salicylic acid degradation tests and also presented the adsorptive and photocatalytic capacity for the discoloration of effluent containing Basazol Yellow 46 L dye.
]]>Colorants doi: 10.3390/colorants2030022
Authors: Anabelle Kriznar
Several medieval mural cycles in Austria were studied from the material and technical point of view, aiming to confirm (or reject) the art-historical hypothesis of their stylistic and workshop connection. These paintings can be found in the churches of Rust (“Fischerkirche”), Marz (Virgin’s Coronation parish church), Kobenz (St. Ruprecht parish church), Ofenbach (St. Veid parish church), and St. Johann am Steinfelde (St. John parish church). They were carried out around 1400 in the International Gothic style. Their workshop connections based on the style are doubtful, therefore, a material and technical study was carried out. Results showed different plaster composition, similar pigment palette, and diverse painting procedures. The murals in Marz, St. Johann, and the older register in Rust reveal important similarities such as plaster composition, predominant a fresco painting technique, the use of natural inorganic pigments, as well as many aspects of the painting procedure and modeling. On the contrary, those in Kobenz, Ofenbach, and the younger register in Rust differ considerably. The second group reveals lower quality in plaster composition, larger a secco parts, addition of synthetic pigments (Kobenz), and a rougher color modeling, indicating less skilled artists. The lower quality also results in a worse conservation state of these murals. The obtained results confirm the same workshop, but different artists in the first group, while in the second group no clear workshop/artist connection could be established.
]]>Colorants doi: 10.3390/colorants2020021
Authors: Adamantia P. Panagopoulou Joanita Vroom Anno Hein Vassilis Kilikoglou
This study attempts to take aspects of pottery technology into account while concentrating on the blue pigment and glaze recipes of various kinds of glazed pottery types; that is to say, Iznik ware, Kütahya ware, Miletus ware, glazed fritware, porcelain, polychrome glazed ware, and monochrome glazed ware were collected from a rescue excavation site within the Castle of Mytilene in Lesvos Island, Greece. The decoration, surface treatment, and production technology were investigated on the basis of 23 ceramic fragments that can be dated to the Turkish/Venetian period. The present study concerns the manufacture of glazed pottery, and in particular, colour recipes and issues of glaze technology. This study endeavoured to look into the specifics of the medieval colour recipes used on the glazed ceramics from Mytilene. This was accomplished by using an analytical process that took into account the compositional information of blue pigments, glazes, and slip coatings. The chemical analysis was conducted using scanning electron microscopy (SEM-EDS), Raman spectroscopy provided information about the compositional variation, and the optical examination via optical microscopy (OM) and scanning electron microscopy (SEM-EDS) yielded information about the sample stratigraphy of the examined ceramic sections. This investigation into glazed ceramics was able to define and reflect the key aspects of each society’s perception of colour through a large variety of colour and glaze recipes.
]]>Colorants doi: 10.3390/colorants2020020
Authors: Isolda Duerto Clara Carrera Daniel Barrios Ana M. Benito Wolfgang K. Maser Belén Villacampa Enrique García-Bordejé María-Jesús Blesa
The importance of counter electrodes in Dye Sensitized Solar Cells (DSSCs) cannot be neglected as they enable the transfer of electrons across the outer circuit, thereby facilitating the reduction reaction of the I3−/I− redox electrolyte. However, the dissolution and deposition of the usual platinum layer on the counter electrode has resulted in contamination concerns. To address this issue, metal-free counter electrodes made of reduced graphene oxide (rGO) aerogels were developed and their catalytic performance towards I3− reduction was evaluated. The reduced graphene materials were characterized, and the fitting analysis of XPS revealed the presence of various nitrogen species, with the primary peaks attributed to pyridinic and pyrrolic nitrogen. The hydrothermal treatment of graphene oxide (GO) resulted in a higher graphitic character and the intensification of the contacts between graphene nanosheets, which should entail higher electrical conductivity, both in-plane and between rGO sheets. Additionally, the presence of nitrogen-provided active sites promoted the catalytic reduction of the electrolyte. Encouragingly, good charge transfer rates were observed between the counter electrode and the electrolyte in the assembled DSSCs, resulting in good photocurrents and exceptional stability over the course of nearly 1200 h after cell assembly. The results obtained suggest that these GO-based systems are promising candidates for developing metal-free counter electrodes for DSSC, supporting the interest of further study.
]]>Colorants doi: 10.3390/colorants2020019
Authors: Anuradha Chowdhury Sridharan Balu Kuo-Wei Lan Louis Wei-Chih Lee Thomas C.-K. Yang
Environmental remediation in the presence of robust semiconductor photocatalysts by utilizing renewable energy sources is of keen interest among researchers. In this study, we synthesize a BiVO4/P-g-C3N4 semiconductor heterojunction photocatalytic system through a hydrothermal route followed by utilizing a total-solvent evaporation method. The optical and electronic properties of the as-prepared heterojunction are characterized via various spectroscopic techniques. Rhodamine B (RhB) and Congo Red (CR) are used as synthetic colorants to evaluate the photocatalytic performances of BiVO4/P-g-C3N4. In addition, the chemical environment of the photocatalyst and its mechanistic pathways are confirmed through X-ray photoelectron spectroscopy and electrochemical Mott–Schottky analysis. The BiVO4/P-g-C3N4 photocatalyst shows higher photodegradation (96.94%) of the mixed synthetic dyes under simulated solar-light irradiation. The as-synthesized BiVO4/P-g-C3N4 heterojunction significantly promotes the quick separation of photoexcited carriers due to the excellent synergetic properties, the extended light absorption, and the photoelectrochemical response. Furthermore, a possible type-II charge transfer mechanism is adopted for the BiVO4/P-g-C3N4 system after investigating the band potentials, active species, and charge carrier migration over the heterojunction interface.
]]>Colorants doi: 10.3390/colorants2020018
Authors: David O. Oluwole Nikoletta B. Báthori
Phthalocyanines (Pcs) are 18-electron π-conjugated macrocyclic ring systems with proven activities in diverse fields, including pharmaceuticals and catalysis. These demonstrated activities are often alluded to as their fascinating photophysical and photochemical dispositions, which are usually dependent on their molecular structures. However, many of these molecules suffer from aggregation due to π–π stacking and have limited insolubility in hydrophilic media, which limits their extensive utilisation in pharmaceutical applications. This review will explore the possibility of fine-tuning the physicochemical properties of phthalocyanines when designed as multicomponent crystals. Among the proven and SMART approaches that have been shown to enhance drug solubility without altering the molecular structure is co-crystallisation. This protocol involves the design and formation of non-covalent interactions between two or more molecular entities to create a supramolecular assembly and subsequently afford multicomponent crystals (MCCs). A systematic review of the Cambridge Structural Database repository yielded several single and multicomponent crystals of Pcs; however, most of them were either salts or solvates, with only a few reports on their co-crystals.
]]>Colorants doi: 10.3390/colorants2020017
Authors: Andrey A. Khodonov Nikolay E. Belikov Alexey Yu. Lukin Alexey V. Laptev Valery A. Barachevsky Sergey D. Varfolomeev Olga V. Demina
Methods for preparation of 5′-substituted spiropyrans, their chemical properties, and the effects of various factors on the relative stabilities of the spiropyrans and their isomeric merocyanine forms are examined, reviewed, and discussed.
]]>Colorants doi: 10.3390/colorants2020016
Authors: Juan C. Stockert Silvina A. Romero Marcelo N. Felix-Pozzi Alfonso Blázquez-Castro
Diaryl-furanones are specific analytical reagents for the biochemical detection of primary amines by fluorescence techniques. Well-known reagents are fluorescamine (Fluram) and 2-methoxy-2,4-diphenyl-3(2H)-furanone (MDPF), yielding fluorescent products with λem at 480–490 nm. Although the reaction products claim to be pyrrolinones, recent studies show that they are really 3-oxopyrrole (pyrrolone) derivatives. Both reagents have been used for the cytochemical demonstration of primary amines. In this work, we have applied the fluorescent products of MDPF with amines (n-butylamine, BA; glucosamine, GA; and spermine, Sp), which showed interesting fluorescence reactions with chromatin DNA. 2,4-diphenyl-3-oxopyrrole products (diPOPy) can be easily synthesized according to well-known procedures, by mixing solutions of MDPF in acetone with water at pH 9 containing the amino compounds. DiPOPy derivatives of BA, GA, and Sp were used for spectroscopic, microscopic, and molecular modeling studies, showing a bright and selective blue–green fluorescence on DNA substrates, mainly chromatin, kinetoplast DNA, and stretched chromatin fibers. The cationic diPOPy fluorophore is planar, with a high partial positive charge in the N atom, and suitable for intercalative binding to DNA. A mechanism of fluorescamine fluorescence due to an inner-salt isomeric form is proposed, and an astonishing correlation between adenine–thymine-rich centromeric heterochromatin in mouse metaphase chromosomes after reaction of the fluorescamine reagent with protein amino groups is also discussed.
]]>Colorants doi: 10.3390/colorants2020015
Authors: Md. Himel Mahmud Md. Tanvir Raihan Md. Tarik Zaman Shakhik Fauzia Tasnim Khan Mohammad Tajul Islam
The textile industry has been exploring sustainable chemicals and natural alternatives to replace harmful and carcinogenic substances used in different stages of textile production for dyeing textiles. Natural dyes are gaining popularity, as they are environmentally friendly and less harmful. Betacyanin, a type of pigment obtained from red pitahaya, commonly known as red dragon fruit (Hylocereus polyrhizus), has peels that are available as agricultural waste and can be used to meet the demand for natural dye production. This study aimed to explore and utilize dragon fruit’s peel as a natural colorant for dyeing 100% cotton knit fabric (scoured and bleached single jersey plain knit) of 170 g/m2, which could transform a low-value material into a valuable product. However, cotton’s phenolic nature and oxidation process result in negative charges on its surface, making natural dyeing challenging. Cationization with cationic agents (ForCat NCH, a mixture of cationic polyamine and 1,3,dichlori-2-propanol) and mordanting (potassium alum or potassium aluminum sulfate) were carried to improve dye exhaustion and enhance colorfastness properties. Spectrophotometer 800 was used to measure color strength (K/S), and several fastness tests, including wash, perspiration, and rubbing were conducted to assess the final product’s performance. The process parameters, such as temperatures, times, pH levels, and dye concentrations were varied to understand better the optimum conditions.
]]>Colorants doi: 10.3390/colorants2020014
Authors: Rihem Jemai Mohamed Amine Djebbi Saber Boubakri Hafsia Ben Rhaiem Abdesslem Ben Haj Amara
Intending to provide efficient and compact wastewater remediation, the present work is exploiting and introducing a novel composite prepared from porous starch aerogel (PSA) and organically modified Ca-montmorillonite (OMMT) for the removal of dyes from aqueous samples. First, potato starch components were used as a hydrolysis precursor to obtain PSA. The organoclay samples were prepared by co-intercalation of octadecylamine (ODA) into Ca-MMT using a low-temperature melting procedure. Composites with different starch-to-organoclay ratios of 10:1, 1:1, and 1:10 were then prepared by a blending process in distilled water and used for methyl orange (MO) uptake. The removal of methyl orange dyes increased with the amount of organoclay in the PSA matrix. Characterization revealed that organoclay synergy improved the PSA surface chemistry, while an important improvement in textural properties and thermal stability was also observed. The composite’s efficiency was demonstrated by high removal capabilities towards MO in most experimental runs, with a maximum adsorption capacity beyond 344.7 mg/g. The fitting result showed that MO adsorption follows a monolayer adsorption model, and chemisorption was the rate-controlling step. Nonetheless, this study proved the great potential of PSA/OMMT in dyeing wastewater treatment. Furthermore, starch modification is proven as an effective approach to enhancing the performance of starch-derived adsorbents.
]]>Colorants doi: 10.3390/colorants2020013
Authors: Abed Haddad Corina E. Rogge
Yves Klein (1928–1962) is best known for his intensely blue monochromatic works made with International Klein Blue (IKB), a synthetic ultramarine blue pigment bound in a poly(vinyl acetate) binder. However, he also made monochromes in other colors, including red and pink, the pigments of which have never been elucidated. Analysis of one sculpture, three paintings, and one screenprint by micro-Fourier transform infrared spectroscopy (µ-FTIR), Raman and surface-enhanced Raman (SERS) spectroscopies, portable X-ray fluorescence spectroscopy (p-XRF), and scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectrometry (EDX), revealed that Klein used, knowingly or unknowingly, a variety of pink and red pigments, including Para Red, rhodamine 6G, rhodamine B, eosin Y, and alizarin lakes. The unexpected variety of pigments contrasts with his use of a single blue pigment and suggests he may not have held a singular vision of what constituted an iconic red or pink color.
]]>Colorants doi: 10.3390/colorants2020012
Authors: Gioele Colombo Anita Cinco G. Attilio Ardizzoia Stefano Brenna
A series of boron difluoride compounds with 2-(imidazo[1,5-a]pyridin-3-yl)phenols bearing alkylic chains at the 1-position has been synthesized and characterized both with 1H and 13C NMR and infrared spectroscopy. This series of compounds displayed blue emission in solution and in thin polymeric films, with interesting features like large Stokes shifts and good fluorescence quantum yields. Time-Dependent Density Functional Theory (TD-DFT) calculations allowed for the identification of the main electronic transitions as intra ligand transitions (1ILT), as corroborated by the Natural Transition Orbitals (NTOs) shapes.
]]>Colorants doi: 10.3390/colorants2010011
Authors: Mahmoud E. Farahat Gregory C. Welch
This work covers the development of non-fullerene acceptors for use in organic photovoltaics built using the N-annulated perylene diimide dye. The classic perylene diimide dye has been extensively used to construct non-fullerene acceptors, leading to device power conversion efficiencies of over 10%. Strong visible light absorption and deep frontier molecular energy levels have made such materials (both molecular and polymeric) near ideal for pairing with narrow-gap conjugated polymers in bulk-heterojunction active layers. The N-annulation of the dye provides an extra site for side-chain engineering and alters the electronic structure of the polycyclic aromatic core. In addition, N-annulation allows for selective bromination of the perylene core, leading to building blocks that are useful for the construction of large molecular frameworks using the atom-economical direct heteroarylation cross-coupling method. Herein, we detail a series of molecules developed by our team that are based on the N-annulated perylene diimide in the form of dimers with different cores (both electron-rich and electron-deficient); dimers with varied side chains; tetramers with varying geometries; and large, asymmetric molecules with internal energy cascades. The use of these molecules as non-fullerene acceptors in organic photovoltaic devices (binary and ternary blends, outdoor and indoor light applications, and spin-coated vs. slot-die-coated photoactive layers) is presented.
]]>Colorants doi: 10.3390/colorants2010010
Authors: Eddie Nahúm Armendáriz-Mireles Carlos Adrián Calles-Arriaga Wilian Pech-Rodríguez Adalberto Castillo-Robles Enrique Rocha-Rangel
In this paper, the potential of marine algae to act as sensitizers is systematically studied and presented. We aim to find a feasible financial strategy to enhance the global efficiency of dye-sensitized solar cells (DSSC). Algae are mainly composed of chlorophylls, carotenoids, flavonoids, and Betalains, which are essential pigments that confer unique characteristics that are required in natural sensitizers. Therefore, this review aims to unveil and understand the underlying mechanism between algae pigments and photoelectrodes and to conduct a comprehensive analysis to determine the effect of algae dye on light absorption efficiency and electron transport. The structural, morphological, optical, and electrochemical impedance properties are deeply analyzed, and we show the current opportunities for natural dyes to be used in energy technologies through DSSC. A comparison of several bibliographic sources dealing with DSSC based on algae provided a general overview of the improvements in factors such as the recombination times, the filling factor, and the Voc values. The contributions of this paper relate to the conversion efficiency and future applications in the DSSC field. Finally, this review exemplifies that the nature of the pigment affects the photophysical properties of the cell. Thus, this paper may contribute to future investigations of DSSC when choosing efficient natural dyes according to their optical and electronic properties. Therefore, this work provides the knowledge required to efficiently merge materials and dyes, in which photovoltaic energy systems’ reproducibility and scalability still represent a challenge. Lastly, this document discusses the natural pigments’ stability and the approaches to improve their chemical stability.
]]>Colorants doi: 10.3390/colorants2010009
Authors: Colorants Editorial Office Colorants Editorial Office
High-quality academic publishing is built on rigorous peer review [...]
]]>Colorants doi: 10.3390/colorants2010008
Authors: Francisco Nobre Jairo Trindade Marcus do Nascimento Giancarlo Souza Otoniel Mendes Anderson Albuquerque Júlio Sambrano Paulo Couceiro Walter Brito Yurimiler Leyet Ruiz José Milton De Matos
This paper reports easy and fast synthesis of PbMoO4 nanocrystals by microwave-assisted hydrothermal (MH) method at different synthesis times (1, 10, 30 and 60 min) at 100 °C. X-ray diffraction, Rietveld refinement and Raman spectroscopy confirm all characteristics of diffraction peaks and active vibrational modes of the pure scheelite structure (tetragonal, I41/a) for all synthesized PbMoO4 nanocrystals. The optical bandgap calculated directly from the samples is close to 3.5 eV. The images collected by scanning electron microscopy show particles with mean length from 159.90(8) nm to 303.02(3) nm with greater exposure of planes (111), (100), (011) and (110). The photocatalytic activity of PbMoO4 nanocrystals against RhB and RBBR dyes resulted in successful degradation in short time intervals using ultraviolet light, where the best performance was achieved for the PbMoO4-10 sample, which was 29.2 and 51.8 times more effective than photolysis. The contribution of oxidant species was monitored by radical scavengers, which confirms that holes (h+) are the main oxidative species in photodegradation of RhB and RBBR dyes, while reuse of the catalyst against RhB and RBBR dyes confirms high stability of the catalyst, although recycled four times.
]]>Colorants doi: 10.3390/colorants2010007
Authors: Noah B. Manz Paul A. Fuierer
The goal of this work was to optimize the combination of natural dyes producing panchromatic absorption matched to the AM1.5 solar spectrum for use in dye sensitized solar cells (DSSCs). Six classes of dyes (Anthocyanins, Betalins, Chlorophyll, Xanthonoids, Curcuminoids and Phycobilins) were explored. UV-Vis data and radial basis function interpolation were used to model the absorbance of 2568 combinations, and three objective functions determined the most commensurable spectrum. TiO2 anodes were sensitized with 42 dye combinations and IV measurements made on simple cells. The absorbance-optimized combination yielded an efficiency of only 0.41%, compared to 1.31% for a simple 1:1 molar ratio of Curcuminoids and α-Mangostin, which showed symbiotic effects. Our results indicate that panchromatic absorption alone is not sufficient to predict optimal DSSC performance, although the mathematical approach may have broader application.
]]>Colorants doi: 10.3390/colorants2010006
Authors: Siti Raihan Hamzah Muhammad Afiq Rosli Nadiah Sabihah Natar Nureel Imanina Abdul Ghani Nur Aien Muhamad Mohammad Saifulddin Azami Mohd Azlan Mohd Ishak Razif Nordin Wan Izhan Nawawi
The textile industry is suffering a great challenge regarding wastewater management, primarily due to the implementation of improper systems, specifically for dye wastewater treatment. Photocatalysis is one of approaches that have been used to treat wastewater. Titanium dioxide (TiO2) was immobilized by using the dip-coating technique in this research. Epoxidized natural rubber (ENR) and polyvinyl chloride (PVC) were used as a polymer to bind the TiO2 on the glass substrate. This immobilized TiO2/ENR/PVC underwent a photoetching process at various times to study the crosslink and porosity formations. Reactive red 4 dye was used as a model pollutant for photocatalytic performance. All immobilized TiO2/ENR/PVC samples under 12, 24 and 30 h of photoetching process (TEP12, TEP24 and TEP30 samples, respectively) showed higher photocatalytic activity compared to those without photoetching process (TEP0 sample) due to the intermediate charge in crosslinking reaction after the photoetching process. The TEP24 sample showed the highest photocatalytic degradation; light harvesting; photocatalytic degradation.
]]>Colorants doi: 10.3390/colorants2010005
Authors: Jeonghee Kang Ketevan Basilashvili Barney Yoo Jong I. Lee
Photoresponsive molecular devices can be a valuable tool to promote chemical changes in response to multiple signals, such as photons and pH, to deliver drugs or to detect physiological conditions in vivo. For example, trans-chalcones (Ct) from 4′-hydroxyflavylium (F1) and 7-hydroxyflavylium (F2) can undergo cis-trans isomerization by photoreaction into many different structures. The isomerization takes place at a slow rate in response to pH change; however, it can be done in seconds by photoreaction. In the investigation, as confirming the previous reports, 3-(2-hydroxy-phenyl)-1-(4-hydroxy-phenyl)-propenone, the trans-chalcone (CtF1) from F1, produces flavylium ions in pH = 1–4.5. Then, we further discovered that the flavylium quickly releases protons to yield the corresponding quinoidal base (A) in a solution of pH = 5.2 during irradiation with 350 nm. Meanwhile, the photolysis of 3-(2,4-dihydroxy-phenyl)-1-phenyl-propenone, the trans-chalcone (CtF2) from F2 at pH = 5.6, induces photoacid behavior by losing a proton from the trans-chalcone to generate Ct2−. The different outcomes of these nearly colorless chalcones under similar pH conditions and with the same photochemical conditions can be useful when yielding colored AH+, A, or Ct2− in a mildly acidic pH environment with temporal and spatial control using photochemical means.
]]>Colorants doi: 10.3390/colorants2010004
Authors: Jacques Burlot Xavier Gallet Gulsu Simsek Franci Ludovic Bellot-Gurlet Philippe Colomban
The study of rare objects requires the use of mobile non-invasive methods such as a portable X-ray fluorescence instrument (pXRF), but this involves an analysis from the outer surface, while the depth analyzed depends on the element measured and, in addition, the material can be very heterogeneous at different scales. The concept of elemental composition, therefore, has no “absolute” meaning for painted enamel decorations. This work evaluates this concept by comparing the pXRF measurements made with different configuration procedures, allowing to evaluate the consequences on the variability of the XRF signals, and discusses the contents of certain chemical elements. For this, two shards from the Qianlong period are analyzed, a shard of blue and white (underglazed) porcelain and a fragment of an ‘imperial’ bowl with painted enamel decoration (huafalang). The variability of measurements is compared for visually appearing homogeneous or heterogeneous areas.
]]>Colorants doi: 10.3390/colorants2010003
Authors: Coralie Pavesi Victor Flon Grégory Genta-Jouve Elodie Pramil Alexandre Escargueil Adeel Nasir Tristan Montier Xavier Franck Soizic Prado
The use of fungal pigments as dyes is attractive for various industries. Fungal pigments arise a strong interest because they are suitable for large-scale industrial production and have none of the drawbacks of synthetic pigments. Their advantages over synthetic or vegetal dyes mark them as a prime target. Azaphilones are fungal polyketides pigments bearing a highly oxygenated pyranoquinone bicyclic core produced by numerous species of ascomyceteous and basidiomyceteous fungi. In order to find new azaphilones dyes, the fungal strain Penicillium hirayamae U., a known producer of azaphilone but, chemically, barely studied so far, was investigated by molecular networking and led to the isolation of three new azaphilones, penazaphilone J-L, along with the known penazaphilone D, isochromophilone VI, and sclerketide E. Their structures were determined based on extensive NMR and the absolute configurations by ECD. All compounds were evaluated for their cytotoxic activity against human cell lines and human pathogenic-resistant strains.
]]>Colorants doi: 10.3390/colorants2010002
Authors: José María Andrés Castán Sana Abidi Tatiana Ghanem Saad Touihri Philippe Blanchard Gregory C. Welch Yulian Zagranyarski Julien Boixel Bright Walker Pierre Josse Clément Cabanetos
Benzothioxanthene imide (BTI) has recently emerged as an interesting and promising block for organic electronics. In this contribution, we report on the impact of the N-annulation of the latter dye on the optoelectronic of π-extended molecular structures. To do so, the thiophene-diketopyrrolopyrrole was selected, as central π-conjugated core, and either end-capped with two BTIs or its N-annulated version, namely the TCI. While almost similar band gaps were measured for individual rylene imide dyes, significant differences were highlighted, and rationalized, on their π-extended counterparts.
]]>Colorants doi: 10.3390/colorants2010001
Authors: Abed Haddad Toni Nakie-Miller Josephine Brilliant Jenks Glen Kowach
Synthetic organic dyes were extensively used by artists in the first half of the 20th century, knowingly or otherwise. This included Andy Warhol and his À la Recherche du Shoe Perdu (c. 1955), a major portfolio of hand-colored prints, a copy of which resides in the collection of The Museum of Modern Art (MoMA). Warhol and his friends were known to use Dr. Ph. Martin’s Synchromatic Transparent Water Colors to bring these prints to life. A historical set of Synchromatic Transparent Watercolors were initially investigated by UV-visible spectroscopy, and samples from the historic set were also characterized by µ-Fourier transform infrared spectroscopy for fingerprint identification. To better elucidate the nature of the mixtures present, thin-layer chromatography was coupled with surface-enhanced Raman spectroscopy to separate the components of all colorants in the set. The dyes decisively identified include Acid Red 73, Acid Red 87, Acid Red 17, Acid Red 103, Basic Red 1, Acid Orange 7, Acid Yellow 23, Acid Green 1, Basic Green 4, Acid Blue 3, Acid Blue 93, Basic Violet 3, Basic Violet 10, Basic Violet 17, and Acid Black 2. Overall, Acid Blue 3, along with Acid Orange 7 and Acid Black 2, were found in the greatest number of dyes in the Dr. Ph. Martin’s set. Data from the historic set was subsequently used for direct comparison with reflectance spectra from the Warhol portfolio using principal component analysis. Microfade testing on a Synchromatic Transparent Watercolors brochure was also conducted to identify fugitive colorants, the results of which were extrapolated to each of the prints in the Warhol portfolio. The analysis provided further insight into the dyes used in À la Recherche du Shoe Perdu and confirmed the extreme light sensitivity of some colorants and the fastness of others.
]]>Colorants doi: 10.3390/colorants1040026
Authors: Anabelle Kriznar Francisco Ager Luis Robles Macías Inés Ortega Feliu Blanca Gómez Tubío Miguel Ángel Respaldiza
Not many manuscript maps have been the object of material analysis so far. A portolan chart, signed and dated by Juan Vespucci in 1520, was studied in this research, conserved at the Archivo General de Indias in Seville (Spain). It is made on parchment and depicts the coasts and islands of Europe and Africa. It is the oldest portolan chart made in Seville, being unusual in applying hand stamp for decorative figures. The map was analysed by different non-invasive techniques: infra-red and ultraviolet light, digital microscope and X-ray fluorescence (XRF). The main goals of this study were to identify the materials used, as well as to detect retouching or restoration work. Results showed that the entire parchment was first covered with a white layer made of lead white (Pb), calcite or gypsum (Ca). The principal pigments used were vermilion (Hg), yellow ochre (Fe), azurite (Cu) and a copper-based green pigment (Cu) and carbon black. The letters were probably written with an iron-gall ink (Fe, Cu). Very thin golden leaves were applied on a mixtion glue for gilded wind roses. Several retouches from the 19th/20th centuries were found using zinc and titanium whites and probably cobalt blue.
]]>Colorants doi: 10.3390/colorants1040025
Authors: Valentina Lorenzon Greta Faccio
Many pigments and dyes are not only valuable molecules in manufacturing, but also environmental pollutants. Stemming from the observation of the slow pace of change taking place to counter the ‘fast fashion’ phenomenon and its environmental consequences, this critical review highlights the importance not only of biotechnological approaches but also of a sustainable leadership to achieve a future-proof fashion industry. Science has been producing sustainable alternatives to counter the issue of dyes, but this is not enough. A change in the business attitude and leadership approach of the organizations that operate in the industry is needed. Only through the successful combination of new technologies and forward-looking decision-making will it be possible to alter the status quo and deal with the multiple environmental challenges that businesses are and will be facing.
]]>Colorants doi: 10.3390/colorants1040024
Authors: Paulina Góra Jolanta Wąs-Gubała
Fragments of single textile fibres are one of the most commonly found microtraces at crime scenes. Among them, the widespread blue and black/grey cotton fibres should be recognized. The analytical methods routinely used in fibre examination mainly focus on color assessment and determination of the fibres’ morphological features as well as chemical composition. This publication presents the physicochemical characteristics of blue and black/grey denim fabrics and fibres as well as an overview of the non-destructive and destructive methods used in the discrimination of these fibres. Usually, such fibre microtraces are very difficult to distinguish in forensic examinations due to their widespread abundance, and, thus, their evidential value is not significant. As previous research shows, most denim material samples were colored with indigo dye. However, due to the changing trends in denim production and the fashion market, indigo derivatives may play a more critical role. The literature review shows significant shortcomings in the development of techniques focusing on the analysis of the dyes contained in denim fibres, and this is a research direction worth pursuing.
]]>Colorants doi: 10.3390/colorants1040023
Authors: Iris Peng Katie Hills-Kimball Isabela Miñana Lovelace Junyu Wang Matthew Rios Ou Chen Li-Qiong Wang
The colors of copper-containing pigments, copper (II) oxide and malachite, and their origins in ceramic glazes were systematically examined over a wide firing temperature range using a suite of analytical and spectroscopy techniques including SEM, UV-Vis FORS, XRD, FTIR, and EPR to gain new insight into the structural and chemical transformations of the glaze during firing. The two colorants investigated were black copper (II) oxide (CuO) nanopowder and blue-green basic copper carbonate, or malachite (Cu2CO3(OH)2), both of which produce a final light blue color following firing. Additionally, silicon carbide (SiC) was used to locally reduce CuO to simulate firing glazes in a reductive environment and produce a final red color. At lower temperatures, malachite was found to decompose to form CuO at 550 °C, elucidating the reason that two different copper colorants could be used interchangeably to form the same “Robin’s Egg Blue” color. At 850 °C, a glaze sintering process occurred, resulting in the distribution of Cu2+ in a square planar geometry and an observed blue color. This structural change occurred at temperatures lower than the glaze’s melting point, indicating that complete vitrification of the glaze is not required for glaze coloration. Conversely, the reduction in Cu2+ to Cu+ through the addition of SiC did not occur until the glaze was fired above the melting temperature (1000 °C), signifying that high temperatures are required for the redox reaction to occur. This study sheds light on intermediate colorant-glaze interactions that are beneficial for understanding and predicting glaze coloring upon exposure to varying temperatures, and the results from this study can be applied to better-controlled glaze production for artists and a deeper appreciation of ceramic glaze chemistry and aesthetics.
]]>Colorants doi: 10.3390/colorants1030022
Authors: Jules C. Picuri Julia M. Natoli Sophia E. Shaw Shruthi P. Shyam Stephen R. VanHoesen Zhenyu Lin Walter J. Bowyer
Hematite, the mineral that gives color to bright red iron ochres, occurs naturally, but there is much evidence that early humans sometimes artificially produced hematite by heating a related mineral, goethite, in wood fires. This represents an important cognitive and technological advance in early human prehistory. Thus, there is a need to distinguish natural hematite from hematite generated by heating goethite in a wood fire. Measuring the line widths of powder X-ray diffraction (XRD) in hematite has been explored, and synthetic goethite heated in a modern furnace has been used as a model system for studying this process. We now show that to be an inappropriate model. Although chemically identical, natural goethite is physically different from and much more variable than goethite produced in a laboratory. Furthermore, by replicating the process using Stone Age technology, we show that heating goethite in a wood fire complicates the interpretation of XRD line widths of the resulting hematite. We conclude that strategies other than powder XRD are necessary to draw conclusions about the ancient processing of iron ochres.
]]>Colorants doi: 10.3390/colorants1030021
Authors: Masafumi Yano Mai Sasaoka Kohei Tamada Misaki Nakai Tatsuo Yajima Koichi Mitsudo Yukiyasu Kashiwagi
Five triphenyltriphenylamines with various substituents were investigated as precursors for near-infrared absorbing materials. Cyclic voltammetry (CV) studies showed that they all give stable radical cations in solution. The radical cations obtained by one-electron chemical oxidation of these compounds show strong absorption in the near-infrared region, and the position of the absorption is strongly influenced by the substituent. DFT (density functional theory) calculations suggest that the introduction of stronger electron-donating substituents would result in a smaller HOMO–SOMO energy gap and thus a larger long wavelength shift, which is consistent with the experimental results. On the other hand, strong electron-withdrawing substituents increase the HOMO–SOMO energy gap, resulting in a short wavelength shift. The position of the near-infrared absorption peak of the triphenylamine radical cation can be controlled to the longer or shorter wavelength direction depending on the substituent. A molecular design of near-infrared absorbing dyes utilizing the electronic effects of substituents is described.
]]>Colorants doi: 10.3390/colorants1030020
Authors: Ryohei Oka Tomoyo Nouchi Toshiyuki Masui
Tb4+-doped sodium zirconate samples, Na2Zr1−xTbxO3, were synthesized as novel environmentally friendly inorganic yellow pigments by a conventional solid-state reaction method. Their crystal structures, optical properties, and colors were characterized. A single-phase form was obtained for the samples in the x range of x ≤ 0.18, while impurity phases were detected for the sample with x = 0.20. All samples showed strong optical absorption in the blue light region, due to the charge transfer transition between O2− and Tb4+. As a result, the sample color became yellow, which is the complementary color of blue, and the color became more vivid with increasing Tb4+ content in the single-phase region. Among the samples, Na2Zr0.82Tb0.18O3 was the optimal composition, with the highest yellowness (b* = +67.2) and pure yellow hue (h° = 90.1). Although the b* value was lower than commercial yellow pigments such as BiVO4 and ZrSiO4:Pr, this sample had a purer yellow hue. Since Na2Zr0.82Tb0.18O3 is composed of non-toxic elements, it could be a new environmentally friendly inorganic yellow pigment.
]]>Colorants doi: 10.3390/colorants1030019
Authors: Mary Virginia Orna Marco Fontani
Naturally occurring and synthetic ancient pigments have a history of use spanning thousands of years. Curiously, some of their newly discovered properties make them excellent candidates for semiconductors, anticounterfeiting agents and so much more. In this paper, we will review their ancient roots in art and modern emergence as 21st century workhorses. You can never judge a pigment by its color alone!
]]>Colorants doi: 10.3390/colorants1030018
Authors: Iuliia Aksenova Elena Bocharnikova Maria Ashmarina
This article compares spectroscopic properties of the series of dipyrromethene dyes, namely their complexes of boron (III), zinc(II) and cadmium(II) with the halogenated ligands of the same structure. Absorption and emission spectra, lifetimes of long-lived emission and quantum yields of luminescence were studied as the functions of molecular structure of dipyrromethene complexes. The role of the position and nature of a substituent in a ligand, polarity of a solvent and temperature of media were also investigated. The studies demonstrate that replacing the central atom boron(III) by zinc(II) decreases the fluorescence quantum yield, indicating the increased role of non-radiative processes in excitation energy deactivations such as intersystem crossings. In addition, according to the heavy atom effect, the efficiency of intersystem crossings in halogen-substituted zinc(II) and cadmium(II) dipyrromethene complexes is higher than in the corresponding boron fluoride dipyrromethenes (BODIPY), which leads to increase in phosphorescence at low temperatures (frozen solutions). The obtained results make it possible to carry out further investigations of potential sensory properties that are required for systematic use of halogenated dipyrromethene complexes for the creation of modern optical oxygen sensors and singlet oxygen photosensitizers for photodynamic therapy or photocatalytic oxidative reactions.
]]>Colorants doi: 10.3390/colorants1030017
Authors: Jianhua Ran Victoria G. Pryazhnikova Felix Y. Telegin
The efficiency of chemoinformatics methods based on a fragment approach for the analysis of relationships between the chemical structure of textile dyes and colour fastness of the dyeings have been shown by examining a large set of properties, including the light fastness of acid dyes on wool and polyamide fibres, the sensitivity of acid dyes on wool to oxygen bleaching, the wash fastness of acid dyes on wool, the adsorption of direct dyes on cotton, and the photodegradation of azo dyes in solution. An analysis of the developed regression models depicted the contribution of ten substructural molecular fragments for each indicator of the colour fastness properties of acid and direct azo dyes on textile materials. The similarity of several individual multi-atomic fragments for acid and direct azo dyes was found for wool, polyamide, and cotton fibres, which indicates the coinciding mechanisms of the physicochemical processes that accompany the destruction of dyes while testing the light fastness and sensitivity of the dyeings to oxygen bleaching, as well as their adsorption/desorption with the wash fastness and dyeability of wool and cotton.
]]>Colorants doi: 10.3390/colorants1030016
Authors: Willem J. de Grip Johan Lugtenburg
Rhodopsin, the first visual pigment identified in the animal retina, was shown to be a photosensitive membrane protein containing covalently bound retinal in the 11-cis configuration, as a chromophore. Upon photoexcitation the chromophore isomerizes in femtoseconds to all-trans, which drives the protein into the active state. Soon thereafter, another geometric isomer—9-cis retinal—was also shown to stably incorporate into the binding pocket, generating a slightly blue-shifted photosensitive protein. This pigment, coined isorhodopsin, was less photosensitive, but could also reach the active state. However, 9-cis retinal was not detected as a chromophore in any of the many animal visual pigments studied, and isorhodopsin was passed over as an exotic and little-relevant rhodopsin analog. Consequently, few in-depth studies of its photochemistry and activation mechanism have been performed. In this review, we aim to illustrate that it is unfortunate that isorhodopsin has received little attention in the visual research and literature. Elementary differences in photoexcitation of rhodopsin and isorhodopsin have already been reported. Further in-depth studies of the photochemical properties and pathways of isorhodopsin would be quite enlightening for the initial steps in vision, as well as being beneficial for biotechnological applications of retinal proteins.
]]>Colorants doi: 10.3390/colorants1020015
Authors: Erman Salih İstifli
Organic azo dyes, which are widely used in industrial, health and cosmetic fields, pose genotoxic risks due to their chemical structures; however, the molecular details of the undesirable effects of these dyes on DNA have been poorly or insufficiently clarified. In this computational molecular docking study, the DNA binding modes and binding affinities of 14 azo dyes, previously determined to show DNA clastogenicity, were characterized using 2 different double-stranded DNA (dsDNA) conformations (an intact dsDNA and dsDNA with an intercalation gap). In this study, it was determined that 10 out of the 14 genotoxic azo dyes were strong dsDNA minor groove binders, while the remaining ones formed tight binding complexes with dsDNA through intercalation or threading intercalation modes. The azo, nitro, hydroxyl, ammonium, sulfonate, naphthalene, methoxyphenyl, bromine, nitrophenyl, imidazole, amino-phenylethanol and chloro-nitrophenyl groups were found to play primary role in the most favorable binding conformations of these dyes on dsDNA with an affinity ranging from −6.35 kcal/mol to −9.42 kcal/mol. It was determined that dsDNA sequences containing GT dinucleotides are frequently preferred in binding by these dyes, and that rings and polar groups are important features for tight binding with dsDNA. It was concluded that these dyes may be banned, or non-genotoxic congeners should be manufactured with appropriate molecular optimization for the genetic health of the human population and for future generations.
]]>Colorants doi: 10.3390/colorants1020014
Authors: Masafumi Yano Kohei Tamada Misaki Nakai Koichi Mitsudo Yukiyasu Kashiwagi
Four triphenylamines with extended π-systems were synthesized. Cyclic voltammetry (CV) measurements showed that they gave radical cations, which are stable in solution. Radical cations obtained upon one electron chemical oxidation showed strong absorption in the near-infrared region. The radical cations of the naphthalene-substituted derivatives show a maximum absorption wavelength above 1000 nm and are classified as NIR-II dyes. Molecular design rules of novel near-infrared absorbing dyes are described.
]]>Colorants doi: 10.3390/colorants1020013
Authors: Fiona Beckett Aaron Shugar
Daylight fluorescent artists’ colors have been well established as fugitive. Upon exposure to light, these vibrant colors can fade and exhibit color shifts. Artwork containing these fluorescent colorants presents complex challenges for art conservators faced with conserving these inherently problematic materials. This paper examined nine fluorescent colorants obtained from Kremer Pigmente, referred to the previous literature and research, and attempted to quantify the visual and photographic observations of fading and color changes. It provides additional information that could be useful in considering conservation documentation and treatment. Fiber optic spectroscopy using ultraviolet and visible light sources was used to measure the spectral shifts of the colorants before and after exposure to light. The fluorescent colors exhibited alterations in intensity coupled with primary peak shifts in the spectrum corresponding to the optical fading and color shifts. Multimodal imaging was executed to analyze the pigments in different regions of the spectrum before and after aging, which has not been documented before with these fluorescent colorants. Imaging in various regions of the spectrum indicated differences in absorption and reflectance between the pigments as captured by a modified camera. The results were compared to recently published research including the identification of the dyes present in the Kremer line of pigments. Multimodal imaging and fiber optic spectroscopy provided valuable information for future documentation and conservation of artworks containing these colorants. Specifically, these non-invasive techniques provide a method to document and identify the spectral changes between the aged and unaged pigment, graph and predict the direction of overall color change, and provide useful data for establishing future conservation treatment protocols.
]]>Colorants doi: 10.3390/colorants1020012
Authors: Junlong Xiong Ka-Wing Yeung Clarence T. T. Wong Wing-Ping Fong Dennis K. P. Ng
Photodynamic therapy (PDT) is an established treatment modality for a range of superficial and localized cancers. There has been tremendous interest in the development of advanced photosensitizers that exhibit superior photophysical properties, high tumor selectivity, and improved pharmacokinetics. Glucose is one of the well-studied targeting moieties that can deliver various therapeutic agents to cancer cells selectively via the Warburg effect. However, the use of glucosylated photosensitizers for targeted PDT has remained little studied and to the best of our knowledge, the PDT effect of the positional isomers of these conjugates has never been compared. We report herein the preparation and photophysical properties of the C1α and C1β anomers of a glucosylated boron dipyrromethene-based photosensitizer. The cellular uptake and photocytotoxicity of both anomers were also studied and compared using A549 human lung carcinoma cells and HEK293 human embryonic kidney cells. Interestingly, the cellular uptake of the C1α anomer was approximately 2-fold higher than that of the C1β anomer regardless of the cell type and incubation time. The uptake pathway of both anomers was also studied. It was found that they were internalized through energy-dependent receptor/protein-mediated endocytosis rather than the well-known glucose transporters and sodium-driven glucose symporters.
]]>Colorants doi: 10.3390/colorants1020011
Authors: Serghey A. Shapovalov
The most important results obtained during the first century of pinacyanol (PIN) application in fundamental and applied research are summarized. The main usages of PIN during the century are described. The structural, protolytic, and thermodynamic properties of the dye in different systems (aqueous and aqueous–organic solutions, premicellar and micellar surfactant systems, and salt-containing solutions) have been analyzed. Quantitative characteristics of intermolecular interactions are considered. Self-association and dissimilar association of PIN with the participation of other dyes, organic ions and molecules, and metal complex compounds under 5 × 10−7–8 × 10−5 mol/L concentrations of PIN are discussed. The analyzed data indicate that at present, as before, the scientific interest in this dye is very high.
]]>Colorants doi: 10.3390/colorants1020010
Authors: Orkun Çoruh Güngör Gündüz Üner Çolak Bora Maviş
Mica-titania pearlescent pigments (MTs) were previously coated with organic molecules to obtain combination pigments (CPs) for achieving certain improvements or functionalities. Anthocyanins (ACNs) are molecules that can be extracted from natural resources and exhibit color changes via pH modifications of the enclosing medium. The purpose of the study was to produce a new series of CPs by depositing ACNs on MTs at different pH values, to observe the changes in color, and to associate these changes to thermogravimetrically determined deposition efficiencies in light of spectral differences. The extraction and deposition methods were based on aqueous chemistry and were straightforward. The ACN deposition generally increased with increasing pH and correlated with the consistency between the charges of the MT surfaces and the dominant ACN species at a specific pH value. The fluorescence of the CPs was inversely correlated with the deposition quantities invoking the possibility of a quenching effect.
]]>Colorants doi: 10.3390/colorants1020009
Authors: Nicolly de Lima Petito Julia Marim Devens Deborah Quintanilha Falcão Fábio Moyses Lins Dantas Thaís Souza Passos Katia Gomes de Lima Araujo
Red bell pepper extract rich in carotenoids was (RBPE) encapsulated with four different encapsulating agents: calcium caseinate (ECC), bovine gelatin (EBG), whey proteins isolate (EWPI), and concentrate (EWPC), aiming to investigate the most effective material to coat and enable the water dispersibility of pigments. Formulations were obtained by the oil in water (O/W) emulsification technique, followed by freeze-drying. Samples were analyzed by encapsulation efficiency, high-performance liquid chromatography (HPLC), Fourier transform infrared spectroscopy (FTIR), dynamic light scattering (DLS), atomic force microscopy (AFM), thermogravimetric analysis (TGA), dispersion stability, and CIELab. Nanoformulations showed a carotenoid encapsulation efficiency of 54.0% (ECC), 57.6% (EWPI), 56.6 % (EWPC), 64.0 % (EBG). Recovered carotenoid profiles from nanoformulations showed similarity to the RBPE, indicating the efficiency of the encapsulation process. Average particle sizes of approximately 109 nm (ECC), 71 nm (EWPI), 64 nm (EWPC), and 173 nm (EBG) were obtained. AFM revealed that all formulations exhibited spherical forms and a heterogeneous distribution profile. Regarding TGA, formulations presented similar thermal behaviors to and lower decomposition speeds than RBPE, suggesting improved thermal stability. Powder formulations were easily dispersed in water (8 mg/mL) and presented intense color and stability to sedimentation for 48 h. Results indicated that all formulations and the chosen technique efficiently increased carotenoid dispersibility in water, indicating their potential to be applied as natural food pigments.
]]>Colorants doi: 10.3390/colorants1020008
Authors: Masanari Namie Jae-Ho Kim Susumu Yonezawa
The surface of polypropylene (PP) was modified with fluorine gas at 25 °C and 10–380 Torr for 1 h. The surface roughness of the fluorinated PP samples was approximately two times larger than that (5 nm) of the untreated sample. The results of Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy showed that the bonds (e.g., -C-C- and -CHx) derived from raw PP decreased and were converted into fluorinated bonds (e.g., -CFx) after surface fluorination. These fluorinated bonds showed higher electronegativity according to the zeta potential results. Fluorinated PP could be stained with the methylene blue basic dye because of the increased surface roughness and the negatively charged surface.
]]>Colorants doi: 10.3390/colorants1010007
Authors: Juan C. Stockert Jesús Espada Alfonso Blázquez-Castro
Melanin and melanoma tumors are two fields of increasing interest in biomedical research. Melanins are ubiquitous biopigments with adaptive value and multiple functions, and occur in the malignant melanoma. Although several chemical structures have been proposed for eumelanin, molecular modeling and orbitals indicate that a planar or spiral benzoquinone-porphycene polymer would be the model that better explains the broad-band light and ultrasound absorption, electric conductivity, and graphite-like organization shown by X-ray crystallography and electron microscopy. Lysosomes and melanosomes are selectively labeled by vital probes, and melanin also binds to metal cations, colorants, and drugs, with important consequences in pharmacology, pathology, and melanoma therapy. In addition to traditional and recent oncologic treatments, photodynamic, photothermal, and ultrasound protocols represent novel modalities for melanoma therapy. Since eumelanin is practically the ideal photothermal and ultrasound sensitizer, the vibrational decay from photo-excited electrons after NIR irradiation, or the electrochemical production of ROS and radicals after ultrasound absorption, induce an efficient heating or oxidative response, resulting in the damage and death of tumor cells. This allows repetitive treatments due to the remaining melanin contained in tumoral melanophages. Given that evolution and prognosis of the advanced melanoma is still a concern, new biophysical procedures based on melanin properties can now be developed and applied.
]]>Colorants doi: 10.3390/colorants1010006
Authors: Olena M. Obukhova Nikolay O. Mchedlov-Petrossyan Natalya A. Vodolazkaya Leonid D. Patsenker Andrey O. Doroshenko
The equilibrium between different tautomers that can be colored or colorless is an important feature for rhodamine dyes. Presently, this phenomenon is mostly discussed for rhodamine B. Herein, we studied the tautomerism and acid–base dissociation (HR+ ⇄ R + H+) of a set of rhodamines in organic media. Form R is an equilibrium mixture of the colored zwitterion R± and colorless lactone R0. Absorption spectra in 90 mass% aqueous acetone reflects the correlation between the dyes structure and the equilibrium constant, KT = [R0]/[R±]. Increase in the pKa value on transferring from water to organic solvents confirms the highly polar character of the R± tautomer. To reveal the role of the solvent nature, the tautomerism of an asymmetrical rhodamine, 2-(12-(diethyliminio)-2,3,5,6,7,12-hexahydro-1H-chromeno[2,3-f]pyrido[3,2,1-ij]quinolin-9-yl)benzoate, was examined in 14 media. This chain–ring tautomerism is an intramolecular acid–base reaction; the central carbon atom acts as a Lewis acid. The interaction with other Lewis acids, Li+, Ca2+, Mg2+, and La3+, results in rupture of lactone cycle. In polar solvents, lactones undergo photocleavage resulting in formation of highly fluorescent R±, whereas the blue fluorescence and abnormally high Stokes shift in low-polar media may be explained either by another photoreaction or by spiroconjugation and charge transfer in the exited state.
]]>Colorants doi: 10.3390/colorants1010005
Authors: Mohammad Tajul Islam Mohammad Sahariar Farhan Farzana Faiza A. F. M. Fahad Halim Afsana Al Sharmin
A systematic review and bibliometric study were undertaken utilizing the Science Citation Index Expanded database from 1990 to 2020 to obtain insights into the trajectory of pigment coloration research. The study focused on the publication performance in terms of the yearly production and citations, as well as mainstream journals, categories of the Web of Sciences, leading nations, well-known institutions, and research trends. The survey found that the yearly output of scholarly publications on pigment coloration research climbed gradually throughout the first quarter of the study period and then increased substantially in the latter five years. The present research emphasis and future trends were examined after summarizing the paper title and abstract analyses, author keyword analysis, and the most regularly used keywords derived from words in KeyWords Plus. To expand its reach in numerous application areas, pigment coloration research will continue to focus on improving pigment qualities.
]]>Colorants doi: 10.3390/colorants1010004
Authors: Anthony Pagan Jong I. Lee Jeonghee Kang
Flavylium ions (6a–6e) were synthesized using Aldol condensation to compare the spectroscopic properties caused by the different numbers and locations of hydroxy groups on the flavylium cations (AH+). Without the addition of acid, increasing the concentration of flavylium ions to 10 mM in ethanol led to the following observation. The flavylium ions with the least number of OH groups (6a and 6b) showed a change in peak at higher concentrations, whereas 6c and 6d did not show the same degree of change in their 1H-NMR signals. This suggests an equilibrium that shifts the isomers B, CE, and Cz more towards the flavylium ion with more OH groups even at low concentrations. One possibility for the cause of this shift is that the flavylium ions become more stable through aggregation. In addition to the NMR results, the UV measurements confirmed that isomers with fewer OH groups showed a more dramatic shift towards the flavylium ion at higher concentrations. Using modeling data at DFT//B3LYP/6311**G(d) level, the self-association was investigated to show that the hydrogen bonding of OH groups is the main player but cannot stabilize entirely without the presence of the chloride ion in the complex.
]]>Colorants doi: 10.3390/colorants1010003
Authors: Serghey A. Shapovalov
The interaction between single- or double-charged anions of bromocresol purple (BP) and cyanine cations (quinaldine blue, QB, or quinaldine red, QR) at concentrations of dyes 5.0·10−7–4.0·10−5 mol/L has been investigated by vis-spectroscopy. The thermodynamic constants of dissimilar associations (Kas) have been studied. Comparison of the values of lg Kas shows that QB− associates of BP− are more stable (6.61 ± 0.07) than QR associates (4.84 ± 0.06); a similar phenomenon is observed for associates of the BP2− anion. Semi-empirical calculations (PM3 method) are in agreement with the vis-spectroscopy data and indicate that the association of dye into an associate is possible. The standard enthalpies of formation of associates (ΔfHo) and energy diagrams have been determined. The ΔfHo data indicate that the formation of an associate between dye ions is an energetically favourable process. The gain in energy significantly exceeds the systematic error of semi-empirical calculations and increases from 157 kJ/mol (associate ”BP− + QB+”) to 729 kJ/mol (associate “BP2− + QR+”). The most probable structures of dissimilar associates are presented. The study of the dissimilar association develops the concept of intermolecular interactions in solutions.
]]>Colorants doi: 10.3390/colorants1010002
Authors: Shu-Kun Lin
On 11 May 2010, the code ISSN 2079-6447 was obtained for Colorants following an application to the ISSN Center in Paris [...]
]]>Colorants doi: 10.3390/colorants1010001
Authors: Anthony Harriman
Colorant: A substance which is used to impart colour to another material! [...]
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