Special Issue "Functional Colorants"

Guest Editor
Dr. Zhi-Min Hao
Brennerstrasse 60, CH-4123 Allschwil, Switzerland
E-Mail:
Interests: pigments; functional chromophores; latent pigments; pigment modifications; pigment solid state characteristics

Dear Colleagues,

Colorants played an important role in the early development of chemical industry as well as the organic chemistry as a scientific discipline.

Indeed, dyestuffs were central to the first Industrial Revolution, which began in the late 18^th century with the mechanization of the textile industries. The rapid spread of cotton mills, and increased productivity in textile manufacturing, encouraged chemists to investigate the composition of natural dyes. They gave the scientific name alizarin to the natural colorant obtained from madder wood extract, which is the basic compound for Turkey Red.

Dyes also played a prominent role in the second Industrial Revolution, when the quest for synthetic colorants led to the development of science-based industry.

The discovery of Mauveine, the first of the modern synthetic dyes, by William Henry Perkin in 1856 marked the beginning of the synthetic dye industry. It stimulated the colorant research by many other chemists. Of particular interest are the discoveries of diazotization and diazo compounds by P. Griess in 1858, Fuchsine by E. Verguin in 1859, and the production of synthetic alizarin (1869) and indigo (1897). In 1875, Otto N. Witt proposed a theory of color and constitution, with the concept of chromophores and auxochromes, which is still used in modern days.

The work by August von Kekulé on the quadric-valence of carbon in 1858, and on the benzene constitution in 1865, paved the way for the analysis, design and synthesis of organic dyes. Armed with the knowledge, C. Graebe and A. Liebermann were successful in the structural elucidation (1868) and subsequent synthesis of alizarin, the key component in the metal complex dye Turkey Red. They were then followed by the structural elucidation (A. von Baeyer, 1883) and the synthesis (K. Heumann, 1890) of indigo.

The development of the synthetic dye industry led to the emergence of classical organic chemistry, which in turn found rapid application in industry. From the end of the nineteenth century the intermediates employed in the manufacture of synthetic dyes found also use in making pharmaceutical products such as aspirin. Some synthetic dyes exhibited bactericidal properties; they were called medicinal dyes. Sulfonamides, drugs introduced in the 1930s, are actually based on research into dyestuffs and their intermediates. Certain classes of dyes have made color photography possible. A close look at the history of chemical industries would reveal a fact that many chemical companies started their business as dyestuff manufacturers in the early days.

The industries of colorants have reached the maturity phase of the life cycle. Like many other mature sectors of the specialty chemicals industry, colorant industries are facing challenges. The past three decades have seen a steady decline in new introductions of dyestuffs for the textile industry, the principal user of dyes. In addition to the maturity factor, in more recent times, there have been increasing impact of energy and raw material cost, and the introduction of stringent toxicological test requirements for new products due to ecological and environmental concerns. As a result, the colorant industries are currently undergoing restructuring and consolidation, and this is likely to continue in the foreseeable future.

On the other hand, there are also plenty of opportunities, especially in those non-traditional application areas where colorants are needed. As a matter of fact, dyes and pigments are today no longer used only for the coloration of textiles, plastics, paints, inks and lacquers but serve as key components in high-tech applications such as reprographics, optical data storage, display devices, dye sensitized solar cells, energy transfer cascades, light emitting diodes, laser welding processes or heat management systems. Dyes are also of growing importance in the medical and biomedical fields. It is interesting to note that in a number of such non-traditional applications, the color is largely irrelevant. It is the ability of the colorants to absorb visible electromagnetic radiation with high efficiency, or other functional property, that is exploited.

Human beings have the intrinsic desire to improve the quality of life. The insatiable demand for better life is one of the key driving forces behind the technological development. What was hard for the average man to imagine yesterday is in every day use today. To move toward a better future, we need to create and develop new materials with new effects for new applications. New colorants are to be designed for desirable functional properties. New functional colorants for non-traditional applications will be the future of innovative colorant research activities, and we look forward to contributions from those areas.

Zhi-Min Hao, Ph.D.
Guest Editor

Related Special Issue

Functional Colorants in the Journal Materials

Submission

All papers should be submitted to ijms@mdpi.org. To be published continuously until the deadline and papers will be listed together at the special issue website.

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• functional dyes
• functional colorants
• colorants for high-tech applications
• dyes for high-tech applications
• chromophores for displays
• dyes for solar cells
• dyes for optical information storage
• dyes for sensing system

Type of Paper: Review
Title: Dental Uses of Coloring Agents
Authors: Jen-Chang Yang and Tsuimin Tsai *
Affiliation: School of Dentistry and Graduate Institute of Biomedical Materials and Engineering, Taipei Medical University, 250 Wu Xing Street, Taipei 110, Taiwan.
E-mails: tmtsai00@tmu.edu.tw; yang820065@gmail.com; Tel. 886-2-273361661 ext. 5203; Fax: 886-2-2739082
Abstract: Colorants are frequently used in food, cosmetics, drugs, and medical devices. The most frequent dental applications of colorants are to provide product identification, mimicking natural tooth colors for dental restoration, and enhancing visual contrast. In addition to simply providing the color, coloring agents have also been used in the diagnosis and treatment of diseases in the oral cavity. This review covers the past, present, and the prosperous future applications of official approved coloring agents in the dental area. Applications in photodynamic therapy and tooth bleaching will be discussed.

Type of Paper: Article
Title: Photonic Crystals for Improved Light Harvesting
Author: Branko Kolaric
Abstract: In this manuscript we show how energy transfer between biomolecules and light itself can be controlled by specially ordered colloidal structure. The fluorescence of chromophores embedded in a photonic crystal is inhibited by the presence of a photonic pseudo-gap. We present the influence of such an incomplete bandgap on the emission and energy transfer by studying the steady-state and time-resolved emission properties of both a donor and an acceptor fluorophore in a self-assembled photonic crystal. Our results clearly show an inhibition of the donor emission and a concomitant enhancement of the acceptor emission, indicating improved energy transfer from donor to acceptor. This is explained by the decreased number of available photonic modes for radiative decay for the donor in a suitable engineered photonic crystal with respect to in the effective homogeneous medium. Branko Kolaric
Abstract: In this manuscript we show how energy transfer between biomolecules and light itself can be controlled by specially ordered colloidal structure. The fluorescence of chromophores embedded in a photonic crystal is inhibited by the presence of a photonic pseudo-gap. We present the influence of such an incomplete bandgap on the emission and energy transfer by studying the steady-state and time-resolved emission properties of both a donor and an acceptor fluorophore in a self-assembled photonic crystal. Our results clearly show an inhibition of the donor emission and a concomitant enhancement of the acceptor emission, indicating improved energy transfer from donor to acceptor. This is explained by the decreased number of available photonic modes for radiative decay for the donor in a suitable engineered photonic crystal with respect to in the effective homogeneous medium.

Type of Paper: Review
Title: Laser Properties of Semiconducting Organic Molecules
Authors: Eva M. Calzado ¹, Pedro G. Boj ² and María A. Díaz-García ^3,*
Affiliations: ¹ Dpto. Física, Ingeniería de Sistemasy Teoría de la Señal and Instituto Universitario de Materiales de Alicante, Universidad de Alicante, Alicante-03080, Spain; E-Mail: evace@ua.es (E.M.C.)
² Dpto. Óptica and Instituto Universitario de Materiales de Alicante, Universidad de Alicante, Alicante-03080, Spain; E-Mail: p.boj@ua.es (P.G.B.)
³ Dpto. Física Aplicada, Unidad asociada UA-CSIC and Instituto Universitario de Materiales de Alicante, Universidad de Alicante, Alicante-03080, Spain
* Author to whom correspondence should be addressed; E-Mail: maria.diaz@ua.es (M.A. D-G.); Tel. +34-965903543; Fax: +34-965909726
Abstract: The aim of this paper is to review the last advances achieved in the field of organic solid-state lasers in relation to the usage of semiconducting organic molecules and oligomers in the form of thin films as active laser media. We mainly focus in the work performed in the last years by our research group. The laser properties of various types of molecules, doped into polystyrene films in waveguide configuration, is described in terms of the observation of amplified spontaneous emission (ASE) by optical pump. The various systems investigated include N,N´-bis(3-methylphenyl)-N,N´-diphenylbenzidine (TPD), several perilenediimide derivatives (PDIs) as well as different types of oligomers based on phenylenevinylenes, thiophenes and thienoacenes. The ASE characteristics, i.e. threshold, emission wavelength, linewidth and photostability are compared with other molecular materials investigated in the literature.
Keywords: lasers; semiconducting molecules; oligomers; amplified spontaneous emission