Volume 6, Issue 9

There are several commercially significant metal complex organic pigments that are based on first row transition metals. The most important of these are the copper phthalocyanine blue and green pigments which find virtually universal use in paints, printing inks, and plastics. These pigments are of such prime importance that they are dealt with separately in three other chapters in this series. This paper describes a group of pigments that are complexes of iron, copper, nickel, and cobalt with polydentate colored ligands of azo, azomethine, oxime, and isoindoline chemical types. The oldest metal complex organic pigment that still finds some use is CI Pigment Green 8, an octahedral oxime iron complex. In the 1970s and 1980s, there was considerable industrial research effort aimed at developing metal complex pigments based on azomethine and isoindoline structures, many of which were found to offer excellent lightfastness, good solvent resistance and thermal stability, although they exhibited rather dull colors. However, several products provide brilliant effects when used in combination with metallic and pearlescent pigments in automotive paints. Many of the pigments introduced have since been withdrawn by the original manufacturers, but a few remain on the market. The synthesis of metal complex pigments generally involves the preparation of the colored ligand, which is then complexed with the transition metal ion

Copper phthalocyanine is the dominant blue organic pigment by far, used extensively in printing ink, paint, plastics, and a range of other applications. A historical perspective of the development of phthalocyanine pigments, from their original serendipitous discovery, through the characterization of their molecular structures, to their development as pigments, is discussed in this chapter and in the separate chapter entitled Phthalocyanines: General Principles. Copper phthalocyanine exhibits polymorphism. The α - and β -forms are the most important crystal phases used as pigments, while the ε -form has only minor significance. Although structurally complex, the synthesis of copper phthalocyanine is relatively straightforward, involving readily available commodity starting materials to provide the products in high yield. After-treatments are required not only to convert the crude pigment into an appropriate pigmentary physical form, but also to provide stability towards crystal phase change and flocculation in application.

Inorganic luminescent pigments (luminescent materials, luminophores, phosphors) as synthetically generated crystalline compositions absorb energy followed by emission of light with lower energy, respectively, longer wavelengths. The light emission occurs often in the visible spectral range. External energy is necessary to enable luminescent materials to generate light. Luminescent pigments are divided into fluorescent and phosphorescent pigments. This classification goes back to different energy transitions. Emission based on allowed optical transitions, with decay times in the order of µs or faster is defined as fluorescence. Emission with longer decay times is called phosphorescence. The occurrence of fluorescence or phosphorescence as well as the decay time depend on structure and composition of a specific luminophore. There are four luminescence mechanisms discussed for inorganic luminescent materials: center luminescence, charge-transfer luminescence, donor–acceptor pair luminescence, and long-afterglow phosphorescence. The emission of luminescent light can have its origin in different excitation mechanisms such as optical excitation (UV radiation or even visible light), high-voltage or low-voltage electroluminescence and excitation with high energy particles (X-rays, γ-rays). Inorganic luminescent pigments are used mainly in fluorescent lamps, cathode-ray tubes, projection television tubes, plasma display panels, light-emitting diodes (LEDs) and for X-ray and γ-ray detection. The pigment particles are dispersed for the applications in specific binder systems. They are applied in form of thin layers and by means of luminophore/solvent suspensions, containing adhesive agents, on a substrate.

Artistic creation has accompanied the development of mankind since the beginning. Color as the appearance of things perceptible with the eye is fundamental for the creative process. For the longest time in the past, the use of color was characterized by often very complex manufacturing processes that required the greatest inventiveness and complex knowledge of comprehensive interrelationships from the user. Existing knowledge was passed on and used again and again, but the basic color materials were always further developed and sensitively adapted to the differentiated areas of application and needs. Today, paint coats and, in some cases, extensive collections of recipes provide us with evidence and ideas about these processes in previous times. In this context, it is important to understand that paint recipes were treated like valuables and secrets in the past. The present overview offers insights into the world of historical pigments, dyes and binders. However, a complete overview is not possible at this point due to the diversity of sources, the individual work processes and the different application requirements.

This article describes the defining characteristics of photochromic dyes and highlights the subset of properties that are of greatest commercial importance. It outlines the history of the industrial exploitation of photochromic colorants before moving on to discuss current and potential applications. In doing so, a brief tour of key types of photochromic dye is provided.

This article outlines the general structures and photochromism characteristic of fulgide dyes and their most important related analogues. It provides an overview of synthetic routes to such derivatives in addition to exemplifying how typical structural variations influence photochromic behavior. A brief survey then follows, giving a flavor of the applications that have been – and continue to be – sought for them in the capacity of functional dyes.