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.

Dr. Zhi-Min Hao
Guest Editor

• 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

• Functional Colorants in Materials (5 articles)