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A special issue of Colorants (ISSN 2079-6447).

Deadline for manuscript submissions: 31 December 2024 | Viewed by 11992

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Prof. Dr. Anthony Harriman

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School of Natural and Environmental Sciences, Newcastle University, Newcastle upon Tyne NE1 7RU, UK
Interests: photophysics; optical spectroscopy; dye chemistry; kinetics; energy and electron transfer; physical chemistry
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Special Issue Information

Dear Colleagues,

We are pleased to announce the Special Issue entitled “Feature Papers in Colorant Chemistry”. We are keen to receive and publish high-quality submissions on any subject relevant to this important field, especially articles concerning structure–colour relationships and applications in sophisticated technologies. The topics of this Special Issue include, but are not limited to, the following:

Synthesis and characterisation of new chromophores;
Functional dyes for advanced technologies;
Quantum chemistry applied to conjugated molecules;
Chromophore–chromophore interactions;
Establishing structure–colour relationships;
Design of interactive molecular arrays;
Advances in optical spectroscopy;
Photonic crystals.

We encourage researchers to submit original research articles, reviews, and communications. For well-prepared papers and those approved for further publication, authors may be eligible for discounts for publication.

Prof. Dr. Anthony Harriman
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Colorants is an international peer-reviewed open access quarterly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1000 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

structure–colour relationships
resonance theory
excitonic coupling
extended pi-conjugation
push–pull chromophores
poly(pyrrolic) dyes
cyanine dyes
stable free radicals
organic triplet sensitisers
solid-state emitters
super-resolution microscopy
opto-electronic devices
artificial light-harvesting arrays
chemical sensors
NIR absorbers
single-molecule emitters

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Published Papers (11 papers)

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Research

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18 pages, 5960 KiB

Open AccessArticle

Use of BODIPY and BORANIL Dyes to Improve Solar Conversion in the Fabrication of Organic Photovoltaic Cells Through the Co-Sensitization Method

by Arcano Matheus Bragança Leite, Higor Oliveira da Cunha, Paula Romanhi, Leandro Ferreira Pedrosa, Rajendran Suresh Babu and Ana Lucia Ferreira de Barros

Colorants 2024, 3(4), 311-328; https://doi.org/10.3390/colorants3040022 - 26 Nov 2024

Viewed by 174

Abstract

This work addresses the implementation of the co-sensitization technique to increase the energy efficiency of organic dye-sensitized solar cells (DSSCs). Fluorescent dyes derived from boron complexes— (BORANIL) and (BODIPY)— were successfully synthesized and used as co-sensitizers in different volume percentage ratios to verify the most effective concentration for photon capture through these sensitizers. The dyes were optically characterized using ultraviolet–visible spectroscopy (UV-VIS) and Fourier transform infrared (FTIR), analyzing them through the optical performance of each hybrid combination of dyes, an optimization of the photon collection capacity in the tests performed in a volume percentage ratio of 25:75 or 1:3. The morphology and surface roughness of the electrodes were analyzed using scanning electron microscopy (SEM) and atomic force microscopy (AFM), respectively. Through electrochemical characterizations, it was found that the highest photovoltaic conversion efficiency was obtained with the ATH1005 (D) dye mixed with ATH032 (G) in the proportion of 25%:75% or DG 1:3, with efficiency (η) of 3.45%, against 2.43% and 1.90% for DG 1:1 and DG 3:1 cells, respectively. Cells with BODIPY dyes also present higher conversion efficiencies compared to BORANIL cells. The results corroborate the presentation of organic solar cells as a viable option for electricity generation. Full article

(This article belongs to the Special Issue Feature Papers in Colorant Chemistry)

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13 pages, 42481 KiB

Open AccessArticle

Pink Hybrid Pigments Resulting from the Adsorption of Congo Red Dye by Zinc Oxide

by Julia de Oliveira Primo, Raphaella Wolf Fleck, Dienifer F. L. Horsth, Andressa dos Santos, Taiane L. Dlugoviet and Fauze J. Anaissi

Colorants 2024, 3(4), 298-310; https://doi.org/10.3390/colorants3040021 - 14 Nov 2024

Viewed by 318

Abstract

Hybrid pigments were obtained by combining zinc oxide with the anionic dye Congo red (CR), a breakthrough with significant environmental implications. By adjusting the ratio of solid mass to dye concentration, it is possible to obtain pigments with pink hues from a white solid (ZnO) through its adsorption of CR. The process involved using ZnO, prepared at 800 °C using cassava starch suspension as a suitable fuel. The oxide was characterized using XRD, SEM, and BET, and the results showed that the textural properties are typical of nanoparticles, with a size of 50.5 nm, a pore size of 3.48 nm, and a surface area of 3.03 nm, making it suitable for molecular dye removal. Controlling the adsorbent mass (in grams) and dye concentration (in mg L⁻¹) makes it possible to consistently produce hybrid pigments in various shades of pink that exhibit good thermal resistance. When dispersed in white waterborne paint, they are chemically stable in different solvents, have excellent painted surface coverage, and resist photochemical degradation. The results demonstrate technical feasibility and compatibility with the Sustainable Development Goals, particularly Goals 6, 11, 12, 14, 15, and 17, offering a promising solution for a more sustainable future. Full article

(This article belongs to the Special Issue Feature Papers in Colorant Chemistry)

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13 pages, 3519 KiB

Open AccessArticle

Optical Characterization of Fluorescent Chitosan-Based Carbon Dots Embedded in Aqueous Natural Dye

by Sthanley R. De Lima, Thiago V. Costa, Tácio T. S. Santos, Dora G. Felipe, Teófanes B. Serna, Acácio A. Andrade and Viviane Pilla

Colorants 2024, 3(4), 269-281; https://doi.org/10.3390/colorants3040019 - 21 Oct 2024

Viewed by 850

Abstract

(1) Background: This work evaluated the optical characterization of aqueous fluorescent chitosan-based carbon dots (or carbon nanoparticles CNPs) embedded in natural dye for potential functional packaging applications. Chitosan-based materials are nontoxic, biodegradable, biocompatible, bactericidal, and produced from renewable polymer sources. Anthocyanins are pigments of different colors with a large range of potential applications, such as in bioindicators and biomonitoring; (2) Methods: The CNPs were synthetized in aqueous solutions using chitosan as a carbon source. The natural dye was extracted from the leaves of Tradescantia pallida Purpurea in aqueous solutions. The fluorescence quantum efficiency (η) and fluorescence lifetime (τ) were determined using the mode-mismatched pump–probe thermal lens (TL) technique and time-resolved fluorescence lifetimes (TRFL) measurements, respectively; (3) Results: The η and τ were measured for CNPs embedded in natural dye solution at different concentrations (5.2, 12.09, and 21.57 mass percentage composition). The η and τ photophysical parameters obtained for CNPs embedded in natural dye were compared with those of other CNPs synthesized using different carbon sources, such as leaves, seeds, and protein; (4) Conclusions: Fluorescence spectra and time-resolved fluorescence measurements corroborate the TL results, and relatively high values of η were obtained for the CNP synthesized and embedded in natural dye. Full article

(This article belongs to the Special Issue Feature Papers in Colorant Chemistry)

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24 pages, 6128 KiB

Open AccessArticle

Easy and Fast Obtention of ZnO by Thermal Decomposition of Zinc Acetate and Its Photocatalytic Properties over Rhodamine B Dye

by Dalete Araujo de Souza, Pedro Hyug de Almeida da Silva, Francisco Paulino da Silva, Yonny Romaguera-Barcelay, Robson Dantas Ferreira, Edgar Alves Araujo Junior, José Fábio de Lima Nascimento, Fagner Ferreira da Costa, Litiko Lopes Takeno, Yurimiler Leyet Ruiz, Lianet Aguilera Dominguez, Walter Ricardo Brito and Francisco Xavier Nobre

Colorants 2024, 3(3), 229-252; https://doi.org/10.3390/colorants3030016 - 23 Sep 2024

Viewed by 718

Abstract

This study presents a simple, low-cost, and efficient route to obtain zinc oxide by adopting the thermal decomposition method of zinc acetate at 300 (Gr@ZnO_300), 400 (Gr@ZnO_400), 500 (Gr@ZnO_500), and 600 °C (Gr@ZnO_600) for 1 h. The diffraction patterns collected for the samples indicated the majority formation of the hexagonal phase (P63mc) for zinc oxide and residual amounts for graphitic carbon, which has a hexagonal structure of space group P63/mmc. The images collected by scanning electron microscopy (SEM) revealed the formation of sub-microcrystals with elongated rod-shaped morphology, with dimensions between 0.223 and 1.09 μm. The optical and colourimetric properties of the obtained materials indicate the presence of graphitic carbon in the samples, corroborating the analysis by XRD and Raman spectroscopy, with an optical bandgap close to 3.21 eV, and energies of the valence (E_VB) and conduction (E_CB) bands of 2.89 eV and −0.31 eV, respectively. The photocatalytic performance at 20 min of exposure time under UV light of all prepared samples in the decolourisation of rhodamine B (RhB) dye solutions follows the order Gr@ZnO_300 (95.6%) > Gr@ZnO_600 (92.8%) > Gr@ZnO_400 (84.0%) > Gr@ZnO_500 (78.1%), where the photocatalytic performance of Gr@ZnO_300 sample was 16.5 times more effective than the photolysis test. Moreover, the results confirmed that the best performance was archived at pH = 10, and the holes (h⁺) and superoxide (O₂^•−) radicals are the main species involved in the discolouration of RhB dye molecules in an aqueous medium. Finally, the reusability experiment shows high stability of the Gr@ZnO_300 sample as a solid photocatalyst and cycling capability, which obtained total discolouration of RhB of a solution under five cycling experiments of 60 min of exposure to UV light at room temperature. Full article

(This article belongs to the Special Issue Feature Papers in Colorant Chemistry)

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15 pages, 5236 KiB

Open AccessArticle

A Multimode Detection Platform for Biothiols Using BODIPY Dye-Conjugated Gold Nanoparticles

by Panangattukara Prabhakaran Praveen Kumar

Colorants 2024, 3(3), 214-228; https://doi.org/10.3390/colorants3030015 - 12 Aug 2024

Viewed by 795

Abstract

This study explored the synthesis and application of BODIPY-functionalized gold nanoparticles (AuNPs) for the sensitive detection of biothiols via an indicator displacement assay coupled with surface-enhanced Raman scattering (SERS) techniques, alongside their efficacy for in vitro cancer cell imaging. Moreover, the assay allowed for the visible colorimetric detection of biothiols under normal and ultraviolet light conditions. The BODIPY (boron-dipyrromethene) fluorophores were strategically conjugated to the surface of gold nanoparticles, forming a robust nanohybrid that leverages the plasmonic properties of AuNPs for enhanced spectroscopic sensitivity. The detection mechanism exploited the displacement of the BODIPY indicator upon interaction with biothiols, triggering a measurable change in fluorescence and SERS signals. This dual-mode sensing approach provides high selectivity and sensitivity for biothiol detection, with detection limits reaching nanomolar concentrations using fluorescence and femtomolar concentration for cysteine using SERS. Furthermore, the BODIPY-AuNP complexes demonstrated excellent biocompatibility and photostability, facilitating their use in the fluorescence imaging of biothiol presence within cellular environments and highlighting their potential for diagnostic and therapeutic applications in biomedical research. Full article

(This article belongs to the Special Issue Feature Papers in Colorant Chemistry)

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12 pages, 2417 KiB

Open AccessArticle

Solid-State Luminescence with a Large Stokes Shift in Starch Functionalized with Low-Content ESIPT Dye

by Emerson Colonetti, Lilian C. da Luz and Fabiano S. Rodembusch

Colorants 2024, 3(2), 99-110; https://doi.org/10.3390/colorants3020007 - 3 Apr 2024

Viewed by 1107

Abstract

Herein, we present the preparation of solid-state photoactive starches with a large Stokes shift, along with the resulting materials. In this investigation, 2-(2′-hydroxyphenyl)benzazole derivatives responsive to intramolecular proton transfer in the excited state (ESIPT) were covalently bonded to the polymeric structure of starch through a reaction involving an isothiocyanate group and the hydroxyl groups of starch. These compounds exhibit absorption at approximately 350 nm, which is related to fully spin- and symmetry-allowed π → π* electronic transitions, and solid-state fluorescence at approximately 500 nm, which features a significant separation between the absorption and emission maxima (~9000 cm⁻¹). Due to the minimal use of fluorophores in functionalized starch preparation, this modification does not affect the original properties of the starch. Finally, photoactive starch-based films with significantly high transparency were successfully produced. Full article

(This article belongs to the Special Issue Feature Papers in Colorant Chemistry)

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11 pages, 4875 KiB

Open AccessArticle

Synthesis of High Near-Infrared Reflective Black Pigment Based on YMn₂O₅

by Kazuki Yamaguchi, Satoru Mochizuki, Yudai Nagato, Takuro Morimoto and Toshiyuki Masui

Colorants 2023, 2(4), 705-715; https://doi.org/10.3390/colorants2040036 - 6 Dec 2023

Cited by 1 | Viewed by 1553

Abstract

Y(Mn_0.95M_0.05)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(Mn_0.95Fe_0.05)₂O₅ and Y(Mn_0.95Ga_0.05)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(Mn_1−xGa_x)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 O_2p and Mn_3d orbitals, and the absorption wavelength of Y(Mn_1−xGa_x)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(Mn_0.85Ga_0.15)₂O₅. Furthermore, this NIR reflectance value was higher than those of the commercially available products (R < 45%). Full article

(This article belongs to the Special Issue Feature Papers in Colorant Chemistry)

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13 pages, 9116 KiB

Open AccessArticle

Repurposing the Strontium Ranelate Antiosteoporotic Drug as a New Outstanding Biocompatible Blue Dye

by Luca M. Sihn, Erick L. Bastos, Marcelo Nakamura, Mayara K. Uchiyama and Henrique E. Toma

Colorants 2023, 2(3), 578-590; https://doi.org/10.3390/colorants2030029 - 13 Sep 2023

Viewed by 1241

Abstract

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. Full article

(This article belongs to the Special Issue Feature Papers in Colorant Chemistry)

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13 pages, 1764 KiB

Open AccessArticle

Adsorption Process of Methyl Orange Dye onto Zinc Hydroxide Nitrate: Kinetic and Thermodynamic Studies

by Daiane Amaral de Ramos Nogueira, Tânia Marina Palhano Zanela, Monielly Viomar Machado, Carlos Alberto Policiano Almeida and Rafael Marangoni

Colorants 2023, 2(3), 565-577; https://doi.org/10.3390/colorants2030028 - 6 Sep 2023

Cited by 2 | Viewed by 1458

Abstract

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. Full article

(This article belongs to the Special Issue Feature Papers in Colorant Chemistry)

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13 pages, 4946 KiB

Open AccessArticle

Enhanced Dyeing of Polypropylene Using Fluorine–Oxygen Gas Mixtures

by Masanari Namie, Jae-Ho Kim and Susumu Yonezawa

Colorants 2023, 2(3), 552-564; https://doi.org/10.3390/colorants2030027 - 31 Aug 2023

Viewed by 1628

Abstract

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 -CH_x) decreased because they were converted into polar groups (-C–O, -CHF-, and -CF_x), 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. Full article

(This article belongs to the Special Issue Feature Papers in Colorant Chemistry)

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Review

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16 pages, 5529 KiB

Open AccessReview

Bimetallic Fenton-like Catalysts in the Remediation of Dyes

by Lydia R. Milam and Roy P. Planalp

Colorants 2024, 3(1), 1-16; https://doi.org/10.3390/colorants3010001 - 21 Dec 2023

Viewed by 1178

Abstract

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. Full article

(This article belongs to the Special Issue Feature Papers in Colorant Chemistry)

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