Traditional Colorants Research Articles

Red phenanthrenequinone dyes with high thermal and photo-stability for LCD color filters

Color filters (CF) are essential integral parts of the liquid crystal display (LCD) and image sensor. Compared to traditional pigment colorants, organic dyes offer a promising alternative to realize CF with improved optical properties and higher resolution. However, organic dyes usually suffer from inferior thermal and photo-stability, limiting their applications in CF. Herein, four robust donor-acceptor organic dyes based on phenanthrenequinone chromophore were designed and synthesized by introducing aromatic amine derivatives as the electron donors. The strong donor-acceptor interactions in these dyes contribute to intense broad charge-transfer absorption bands from 375 nm to 600 nm with high molar extinction coefficients, thus realizing red color. Also, these dyes exhibit high thermal and photo-stability, good compatibility with the polymer binder and low aggregation tendencies, resulting in high thermal and photo-stability for the fabricated CF films. Remarkably, among these phenanthrenequinone dyes, DTPAP with multi-donor substitution and extended π-conjugation exhibited the best performance in terms of molar extinction coefficient, thermal and photo-stability, contributing to the highest thermal and photo-stability for the CF film with color difference values (ΔEab) below 0.75 under simulated industrial manufacturing processes. This work confirms that phenanthrenequinone is a robust chromophore and is conducive to developing thermal and photo-stable CF dyes, and paves a way to improve the optical properties and stability of donor-acceptor dyes for CF.

Non-invasive study of the dyes and pigments in the Chinese woodblock New Year paintings

Woodblock New Year painting is a traditional Chinese folk art that flourished during the 19th and early 20th centuries. These paintings feature a wide variety of colors, particularly after the introduction of synthetic colorants from Europe in the late 19th century. The scientific identification of dyes and pigments used in these paintings can provide valuable insights into the socio-historical context of the time. However, the history of materials used in the printing of New Year paintings is still lacking adequate information. In this study, we employed a combination of spectroscopic and imaging techniques, including Macro X-ray fluorescence imaging (MA-XRF), hyperspectral imaging, and Raman spectroscopy to identify the dyes and pigments used in two Yangliuqing New Year paintings. Our analysis revealed the presence of both traditional pigments and synthetic colorants, such as vermilion, Prussian blue, and methyl/crystal violet. We also discovered several color-matching techniques used to create light pink, light orange, and dark purple hues. These findings suggest that synthetic colorants were gradually replacing traditional pigments in China due to the growth of global trade at that time. Furthermore, our research provides valuable information for the conservation, preservation, and display of New Year paintings.

Ultralight plasmonic structural color paint.

All present commercial colors are based on pigments. While such traditional pigment-based colorants offer a commercial platform for large-volume and angle insensitiveness, they are limited by their instability in atmosphere, color fading, and severe environmental toxicity. Commercial exploitation of artificial structural coloration has fallen short due to the lack of design ideas and impractical nanofabrication techniques. Here, we present a self-assembled subwavelength plasmonic cavity that overcomes these challenges while offering a tailorable platform for rendering angle and polarization-independent vivid structural colors. Fabricated through large-scale techniques, we produce stand-alone paints ready to be used on any substrate. The platform offers full coloration with a single layer of pigment, surface density of 0.4 g/m2, making it the lightest paint in the world.

Multi-analytic characterization of colorants in two impressions of an Utagawa Toyoharu perspective print

Abstract Two impressions of an Utagawa Toyoharu (1735–1814) perspective print were used to develop an analytical protocol for investigating traditional Edo period Japanese ink colorants. Characterization of these often sensitive colorants can help guide policies regarding the preservation of Edo period Japanese prints. As there are some visual similarities and notable differences in the colors in the two impressions, another goal of the study was to determine the correlation of the color palettes used in both impressions. This study compares the colorants in the prints to reference samples using accessible non-invasive techniques, focusing on multimodal imaging and reflectance spectroscopy. XRF and Raman spectroscopy are used to supplement analyses. Results indicate that the color palettes in the two impressions are similar and the visual differences are due to a coating on one of the prints and differing preservation histories. The study details a successful approach for the characterization of Edo period print colorants using primarily multimodal imaging and reflectance spectroscopy, while showing their limitations.

A blue can conceal another! Noninvasive multispectroscopic analyses of mixtures of indigo and Prussian blue

AbstractBlue colors were sparsely used in the first colored Japanese ukiyo‐e prints but became predominant during the 19th century, mainly due to the integration of the synthetic Prussian blue in the palette of the printers around 1830. For a long time, researchers have assumed that the traditional Japanese organic blue colorants such as indigo were substituted by cheaper Prussian blue. Some analytical studies conducted on such artworks showed evidence of the common use of indigo and Prussian blue in Japanese paintings, alone or mixed together. Recent measurements carried out on bluish areas of an ukiyo‐e designed by Utamaro showed the simultaneous use of the two pigments. However, if visible reflectance spectroscopy suggested the single use of Indigo, Fourier transform infrared spectroscopy (FTIR) also indicated the presence of Prussian blue. These results question about the possible identification of all the pigments of a colored mixture by using a single analytical technique. Without using FTIR spectroscopy, the Prussian blue would not have been detected, whereas on infrared spectra the expected specific bands ascribed to indigo are not identified. The objective of this work is to investigate mixtures of pigments, using noninvasive spectroscopic techniques in order to assess their limits of detection. Fluorimetry, hyperspectral imaging, and infrared spectroscopies have been performed on three color charts made of indigo, Prussian blue, and mixtures of them at different proportions of matter. The results emphasize the systematic identification of Prussian blue thanks to infrared spectroscopy, whereas the identification of indigo, mixed with Prussian blue, appears to be more challenging.

Creation and reference characterization of Edo period Japanese woodblock printing ink colorant samples using multimodal imaging and reflectance spectroscopy

The Library of Congress Prints and Photographs Division holds a large collection of Edo period (1615–1868) nishiki-e, Japanese multicolored woodblock prints. The sensitivities of some of the traditional colorants to environmental and conservation treatment factors results in numerous preservation concerns. Characterization of colorants in these prints can help guide preservation policies, however, identification of colorants can be difficult and re-creation methodologies for reference samples have been elusive. This paper details reproducible colorant preparation methods and characterizes these samples using accessible non-invasive techniques, multimodal imaging and reflectance spectroscopy. A majority of the colorants can be identified using the two techniques as complementary methods.

Influence of environment on the stability of Chinese traditional colorants

Artists use traditional Chinese colorants extensively in contemporary artworks, mainly brilliants and dyes derived from natural raw materials. Colorant fading caused by ultraviolet (UV) light has b...

Regional variation in components and antioxidant and antifungal activities of Perilla frutescens essential oils in China

Perilla frutescens is an important annual herb of the mint family that is native to East Asia, particularly China, Korea, and Japan, is widely used as a fresh vegetable and in traditional Chinese medicines, popular garnishes, and food colorants. Hydrodistilled essential oils obtained from P. frutescens from 11 areas of China were analyzed by gas chromatography-mass spectrometry (GC–MS). One hundred and nineteen compounds accounting for 98.07–99.74% of the oils were identified. The predominant compounds were 2-acetylfuran (max. 82.17%), perillaldehyde (max. 53.41%), caryophyllene (max. 38.34%), laurolene (max. 40.6%), 2-hexanoylfuran (max. 33.03%), 2-butylamine (max. 22.22%), α-asarone (max. 11.85%), β-farnesene (max. 9.25%), α-caryophyllene (max. 9.16%), and (Z,E)-α-farnesene (max. 7.14%). Chemical variation in the oils was estimated using cluster analysis and principal component analysis. The results revealed chemical polymorphism in the oils. However, the oils from Ganzhou, Kaili, Suining, Macheng, Nanyang, and Yixing were more similar, and the oils from Quzhou, Loudi, and Nanning also revealed similarities. Antioxidant activity (by free radical scavenging activity and ferric reducing power) and antifungal activity (by poisoned food method and micro-well dilution method) were also assessed. The antioxidant activity of the oils showed similar order to that obtained by three different testing methods: Pingliang, Baoding, Loudi, and Quzhou>Kaili, Ganzhou, Macheng, and Nanning>Suining, Nanyang, and Yixing. All oils except that from Baoding were active against all of the tested strains. These results suggested that the region of origin greatly influenced the chemical composition and bioactivities of P. frutescens, which might help in developing this promising bioresource in the food and pharmaceutical industries.

Deletion of pigR gene in Monascus ruber leads to loss of pigment production

Pigments produced by Monascus are traditional food colorants and are widely used as dietary supplements. Since genes involving in pigment biosynthesis have not been reported, we describe the identification of a putative pigment-regulatory gene (pigR) obtained by molecular analysis of an albino strain of Monascus ruber M7. In the pigR-deleted strain (ΔpigR), neither the pigments nor pigR expression were detected by HPLC or reverse-transcription PCR, respectively, whereas the introduction of the pigR, together with a constitutive trpC promoter into ΔpigR, caused it to produce 5.4U of red pigments/g dry mycelia, about 12-fold higher than Monascus ruber M7 (0.46U/g dry mycelia). Thus pigR up-regulates pigment production in Monascus ruber M7.

Determination of Beet Root Betanin in Dairy Products by High-Performance Liquid Chromatography (HPLC)

The food industry uses different additives to give foods and beverages the appearance expected by the consumer. Among them, pigments of natural origin are receiving increasing attention due to safety concerns about traditional colorants and the relevance of a healthy diet. This experiment describes the quantitative determination of the characteristic pigment of red beet roots in dairy foods such as conventional yogurt, drinking yogurt, and fromage frais of strawberry, blackberry, and apricot varieties. The laboratory experiment is suitable for an undergraduate instrument analysis course and introduces the principles involved in chromatographic techniques and the use of high-performance liquid chromatography (HPLC) equipment. It also opens the discussion to other concepts such as carbon chirality, absorbance, and the requirements of food additives.

Simple, Highly Efficient Vacuum‐Processed Bulk Heterojunction Solar Cells Based on Merocyanine Dyes

AbstractIn order to be competitive on the energy market, organic solar cells with higher efficiency are needed. To date, polymer solar cells have retained the lead with efficiencies of up to 8%. However, research on small molecule solar cells has been catching up throughout recent years and is showing similar efficiencies, however, only for more sophisticated multilayer device configurations. In this work, a simple, highly efficient, vacuum‐processed small molecule solar cell based on merocyanine dyes – traditional colorants that can easily be mass‐produced and purified – is presented. In the past, merocyanines have been successfully introduced in solution‐processed as well as vacuum‐processed devices, demonstrating efficiencies up to 4.9%. Here, further optimization of devices is achieved while keeping the same simple layer stack, ultimately leading to efficiencies beyond the 6% mark. In addition, physical properties such as the charge carrier transport and the cell performance under various light intensities are addressed.

THE BENEFITS AND RISKS OF ANOXIC DISPLAY FOR COLORANTS

Tate is undertaking a major research project to assess the effects of anoxic storage on paper-based works of art. The outcomes will include: the design of a safe, affordable anoxic framing system suitable for both storage and display, capable of being incorporated into historic frames; guidelines on materials which would be harmed by anoxia and information on their recognition and behaviour. Such framing would provide safer access to paper-based works of art. This paper reviews the following materials found in paper-based works of art that are susceptible to oxidation and which could therefore benefit from anoxia: traditional colorants; modern pigments; graphic media; printing, copying or photographic processes; and oil or alkyd media. Materials, predominantly colorants, which may be susceptible to reducing reactions that proceed in the absence of oxygen, are identified for later study into their behaviour and their non-destructive identification on paper-based works of art.

Bulk heterojunction organic solar cells based on merocyanine colorants

Traditional low-molecular weight colorants that are widely applied in textile coloration, for printing purposes and nonlinear optics, now afford bulk heterojunction solar cells in combination with soluble C(60) fullerene derivative PCBM with power conversion efficiencies up to 1.7% under standard solar radiation.

Dyes and other colorants in microtechnique and biomedical research

Dyes and other colorants in microtechnique and biomedical research

Analysis of Metallic Pigments Used in 19th Century Japanese Prints

Japanese color woodblock prints ("ukiyo-e") from the Edo (1615-1868) and Meiji periods (1868- 1912) are among the most celebrated examples of color printmaking in the world. Full-color prints became technically and commercially viable around 1765. Traditional ukiyo-e colorants were watersoluble, uniform, translucent, organic (vegetal) and inorganic pigments of very small particle size. (Synthetic colorants were also introduced from the West in the 19th C, probably beginning with "Prussian blue" in the 1820s.) A pigment was applied with a brush to a color block, and then rice flour paste was mixed with the pigment to thicken it, facilitate control and rubbing into the paper, improve the uniformity of the colorant, and avoid a dry or granular texture. The dampened paper, sized with cooked bovine skins and alum, was then placed on the block (aligning with registration marks cut into the blocks). The colorants were then pressed into the paper by rubbing a bamboo pad against the back of the paper so that the colors were absorbed on the front surface.

Non-destructive analysis of organic pigments and dyes using Raman microprobe, microfluorometer or absorption microspectrophotometer

AbstractThe use of Raman microanalysis, together with related techniques of absorption microspectrophotometry and fluorometric microanalysis, for investigating dyes and pigments is described. Examples are given of the identification of a number of synthetic and traditional colorants.

The Ozone Fading of Traditional Japanese Colorants

The Ozone Fading of Traditional Japanese Colorants

The ozone fading of traditional Japanese colorants

The colorfastness of several traditional Japanese colorants upon exposure to atmospheric ozone was tested in a chamber exposure experiment. Samples, in the form of colorants applied to paper, dyes on silk cloth, and colorants on a nineteenth- century Japanese woodblock print, were exposed to an atmosphere containing 0•40 parts per million ozone at 220C and 50% RH, in the absence of light, for 12 weeks. Color differences, calculated from the measured diffuse reflectance spectra, were used to assess the rate and extent of the ozone fading. Of the colorants applied to paper, orpiment was the only inorganic pigment that showed severe color loss after ozone exposure. Several organic colorants on paper also reacted, including the widely used plant colorants ɑi (indigo) and ukon (turmeric). The woodblock print, produced using the plant-derived colorants beni (safflower), ɑi (indigo), shio (gamboge) and aigami (dayflower), showed significant ozone fading only in the blue and green areas, which contain ɑi. Several of the dyed silk cloths also exhibited some color change in this experiment, suggesting that prolonged exposure to atmospheric ozone could pose a risk to these materials as well.

The Ozone Fading of Traditional Natural Organic Colorants on Paper

This report details the results of an ozone exposure experiment performed on a large number of traditional natural organic colorants applied to watercolor paper with no binder. These colorants were exposed in an environmental chamber to an atmosphere containing 0.397 ± .007 parts per million (ppm) ozone at 72°F and 50% RH in the absence of light for 12 weeks. This ozone concentration is typical of that found in the Los Angeles atmosphere during a heavy smog episode. The total ozone dose delivered to the samples is equivalent to about four years of exposure to outdoor air in Los Angeles or to about eight years inside a typical air conditioned building in Los Angeles.The ozone sensitivity of these colorant systems was evaluated by monitoring the color changes which occurred during the exposure. Almost all colorant systems tested showed some degree of fading after ozone exposure, and a few of these (curcumin, dragon's blood, indigo, and madder lake) should be considered very ozone-fugitive.

The Ozone Fading of Traditional Natural Organic Colorants on Paper

This report details the results of an ozone exposure experiment performed on a large number of traditional natural organic colorants applied to watercolor paper with no binder. These colorants were exposed in an environmental chamber to an atmosphere containing 0.397 ± .007 parts per million (ppm) ozone at 72°F and 50% RH in the absence of light for 12 weeks. This ozone concentration is typical of that found in the Los Angeles atmosphere during a heavy smog episode. The total ozone dose delivered to the samples is equivalent to about four years of exposure to outdoor air in Los Angeles or to about eight years inside a typical air conditioned building in Los Angeles.The ozone sensitivity of these colorant systems was evaluated by monitoring the color changes which occurred during the exposure. Almost all colorant systems tested showed some degree of fading after ozone exposure, and a few of these (curcumin, dragon's blood, indigo, and madder lake) should be considered very ozone-fugitive.