Complex Azo Dyes and Pigments

There are a number of particular technical advantages associated with the formation of coloured metal complexes. Commonly, the transition metal complexes of a coloured organic ligand exhibit lightfastness which is significantly better than that of the free ligand. An explanation that has been offered for this effect is that coordination with a transition metal ion 

In terms of fastness properties, carbonyl dyes and pigments are often superior to their azo counterparts. They are thus commonly the colorants of choice when high technical performance is demanded by a particular 

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Azo dyes and azo pigments are the most important class of both non-metallized and metallized colorants. Therefore, this section is devoted entirely to metal complex azo dyes and pigments. 

Dyes and Pigments. Several thousand metric tons of metallated or metal coordinated phthalocyanine dyes (10) are sold annually in the United States. The partially oxidized metallated phthalocyanine dyes are good conductors and are called molecular metals (see Semiconductors Phthalocyanine compounds Colorants forplastics). Azo dyes (qv) are also often metallated. The basic unit for a 2,2 -azobisphenol dye is shown as stmcture (11). Sulfonic acid groups are used to provide solubiHty, and a wide variety of other substituents influence color and stabiHty. Such complexes have also found appHcations as analytical indicators, pigments (qv), and paint additives. 

The yellow ink jet dyes (and pigments) are metal-free azo dyes, such as Cl Direct Yellow 132 and Cl Acid Yellow 23 (Tartrazine).48,49 Most of the magentas are azo dyes derived from H-acid (l-amino-8-naphthol-3,6-disulfonic acid), such as (62), and xanthenes, such as Cl Acid Red 52 and Cl Acid Red 289.48,49 Where high lightfastness is a requirement, a copper complex azo dye, Cl Reactive Red 23 (63), is used. However, such dyes are dull (see Section 9.12.3.2). Nickel complex PAQ dyes, such as (22), are claimed to be brighter and to have similar high lightfastness... 

Some coordination compounds have been used as dyes and pigments, but it must be admitted that these applications developed without reference to the fact that the compounds are complexes. Examples of paint pigments are Prussian blue and the phthalocyanines metallized azo dyes are common in the textile industry. 

This chapter is concerned with dyes and pigments which are complexes of azo, formazan, azomethine, nitroso, anthraquinone and phthalocyanine ligands. Many of these compounds find important applications in other fields, particularly colour photography and reprography, analysis, catalysis, biology, and some modem high technology industries such as electronics. These applications are described in other chapters of this volume. 

Metal-dye complexes play a very important role in dyestuff technology and find applications in many other fields, e.g. in analytical chemistry.119-123 Except for copper phthalocyanine, metal-azo compound complexes are the most important and the most widely used as dyes and pigments. Typical precursors are shown in Scheme 1. 

A variety of azo and methine dyes and pigments have been examined in conjunction with PVK and other polymers, but the patent literature indicates that virtually any dye or pigment can sensitize the photoconductivity of PVK into the visible range. When photogeneration proceeds via electronic transitions involving both the polymer and the dye (such as a charge-transfer complex between PVK and the acceptor part of the dye), the process is also considered intrinsic. When these transitions proceed within the dye molecules or pigment particles, the process is termed extrinsic. 

Impact PS Good light stability. Must withstand temperatures up to 280X Yellow and red toners Polycyclics Isoindolinone Selected Bis-arylamides Phthalocyanine Blue Phthalocyanine Green Metal complex Selected dyes Cadmium pigments Ultramarine Blue Azo condensation Special monoazos... 

The l-phenylazo-2-naphthol (7) and particularly the 2-phenylazo-l-naphthol (8) systems are used extensively, providing many of the commercial metal complex azo colorants. Azo pigments are derived from (7) whilst azo dyes are obtained from (8). Both these types of colorant exist predominantly, if not exclusively, in the hydrazone tautomeric form.8,9... 

The use of metal complex dyes for textile and related applications has already been treated comprehensively.7 There have been few major advances since that review. Therefore, this section focuses on typical commercial metal complex dyes, key structure-property relationships, and some recent studies on metal complex azo pigments. 

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