Colorants

13 pages, 1602 KiB

Open AccessArticle

Can X-ray Diffraction Distinguish Natural from Anthropogenic Hematite? Replication of the Conversion of Natural Goethite in Both Furnace and Campfire

by Jules C. Picuri, Julia M. Natoli, Sophia E. Shaw, Shruthi P. Shyam, Stephen R. VanHoesen, Zhenyu Lin and Walter J. Bowyer

Colorants 2022, 1(3), 363-375; https://doi.org/10.3390/colorants1030022 - 06 Sep 2022

Cited by 1 | Viewed by 1453

Abstract

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Colorants: Ancient and Modern)

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9 pages, 2277 KiB

Open AccessArticle

Substituent Control of Near-Infrared Absorption of Triphenylamine Radical Cation

by Masafumi Yano, Mai Sasaoka, Kohei Tamada, Misaki Nakai, Tatsuo Yajima, Koichi Mitsudo and Yukiyasu Kashiwagi

Colorants 2022, 1(3), 354-362; https://doi.org/10.3390/colorants1030021 - 01 Aug 2022

Cited by 1 | Viewed by 2353

Abstract

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Colorants: Ancient and Modern)

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7 pages, 2384 KiB

Open AccessArticle

Synthesis and Color Evaluation of Tb⁴⁺-Doped Na₂ZrO₃ for Inorganic Yellow Pigments

by Ryohei Oka, Tomoyo Nouchi and Toshiyuki Masui

Colorants 2022, 1(3), 347-353; https://doi.org/10.3390/colorants1030020 - 01 Aug 2022

Cited by 1 | Viewed by 1738

Abstract

Tb⁴⁺-doped sodium zirconate samples, Na₂Zr_1−xTb_xO₃, 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 [...] Read more.

Tb⁴⁺-doped sodium zirconate samples, Na₂Zr_1−xTb_xO₃, 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 Na₂Zr_0.82Tb_0.18O₃ is composed of non-toxic elements, it could be a new environmentally friendly inorganic yellow pigment. Full article

(This article belongs to the Special Issue Colorants: Ancient and Modern)

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40 pages, 9659 KiB

Open AccessReview

The Modernity of Ancient Pigments: A Historical Approach

by Mary Virginia Orna and Marco Fontani

Colorants 2022, 1(3), 307-346; https://doi.org/10.3390/colorants1030019 - 13 Jul 2022

Cited by 3 | Viewed by 6765

Abstract

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 [...] Read more.

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! Full article

(This article belongs to the Special Issue Colorants: Ancient and Modern)

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9 pages, 2294 KiB

Open AccessArticle

Photonics of Halogenated Zinc(II) and Cadmium(II) Dipyrromethene Complexes

by Iuliia Aksenova, Elena Bocharnikova and Maria Ashmarina

Colorants 2022, 1(3), 298-306; https://doi.org/10.3390/colorants1030018 - 09 Jul 2022

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Abstract

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Colorants: Ancient and Modern)

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18 pages, 38547 KiB

Open AccessArticle

Chemoinformatics Analysis of the Colour Fastness Properties of Acid and Direct Dyes in Textile Coloration

by Jianhua Ran, Victoria G. Pryazhnikova and Felix Y. Telegin

Colorants 2022, 1(3), 280-297; https://doi.org/10.3390/colorants1030017 - 05 Jul 2022

Cited by 3 | Viewed by 1858

Abstract

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Colorants: Ancient and Modern)

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24 pages, 2006 KiB

Open AccessReview

Isorhodopsin: An Undervalued Visual Pigment Analog

by Willem J. de Grip and Johan Lugtenburg

Colorants 2022, 1(3), 256-279; https://doi.org/10.3390/colorants1030016 - 23 Jun 2022

Cited by 1 | Viewed by 1990

Abstract

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Colorants: Ancient and Modern)

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Colorants, Volume 1, Issue 3 (September 2022) – 7 articles

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