Basic dyes methine

The distribution of each chemical type between the major application groups of colorants is far from uniform (Table 1.1). Stilbene and thiazole dyes are almost invariably direct dyes, also containing one or more azo groups. Acridines and methines are usually basic dyes,... 

The name of this structural class ( quinoline ) in the Colour Index is not ideal because quinoline derivatives feature in other related classes, such as the methine basic dyes with a quinolinium cationic group. The class is more precisely associated with quinophthalone (1.15), the characteristic chromogen derived by condensation of quinoline derivatives with phthalic anhydride. This small class of yellow compounds contributes to the disperse, acid, basic and solvent ranges of dyes. 

Most of these products are azo or anthraquinone types, often with a localised quaternary ammonium group isolated from the chromogen by a saturated alkyl chain, as in Cl Basic Red 18 (1.52). Such products often exhibit higher light fastness than the traditional delocalised types. Improved azomethine, methine and polymethine basic dyes of good light fastness are also available. In contrast to the more specialised traditional classes, the azo and methine dyes have contributed to the basic dye range across the entire spectrum of hues (see Table 1.6) and now account for a clear majority of all basic dyes listed in the Colour Index. 

Most of the basic dyes used for the polyacrylonitriles belong to the more recently developed azo and anthraquinone groups, as well as the methines. An example of an azo dye is ... 

A typical methine basic dye is, for example, C.I.S166 which has the structural formula ... 

Cationic dyes include the basic dyes and some of the mordant dyes that are designed to bind acidic sites on a substrate, such as fibers. Useful t5q>es of such dyes include the azo compounds, diphenylmethane compounds, triarylmethanes, xanthene compounds, acridine compounds, quinoline compounds, methine or polymethine compounds, thiazole compounds, indamine or in-dophenyl compounds, azine compounds, oxazine compounds, and thiazine compounds. 

Basic dyes are triarylmethane, xanthene, azine, oxazine, thiazine and acridine derivatives. Azo and methine dyes are encountered particularly as colouring agents for polyacrylonitrile fibres. 

Methine basic dye. Strictly, the name Astrazon pink FG applies to the chloride. 

Hamer s book in this series (1). which reviewed the synthesis of sensitizing dyes, their physical characteristics, and general photographic properties up to 1958, remains the basic encyclopedic source for the study of methine dyes. 

Another objective is to discuss briefly recent and major trends in the field of methine dyes color. Indeed, because of its relatively simple structure, the thiazole ring has been chosen in the past for studying color-structure relations. Using Brooker s basicity concepts (5), numerous valuable attempts in different countries succeeded in establishing semiempirical rules for explaining the effects of structural changes on color. 

The use of sensitizing dyes in photography has been the subject of many studies and constitutes. still now. one of the most studied areas in specialized periodic publications (125, 126) or in textbooks (88. 127). It can be ascertained that one hundred years after Vogel s discovery of spectral sensitization, the basic mechanisms of action of dyes on their silver halide support still remain not fully understood. However, the theoretical reasons explaining why among many other dye families practically only cyanine methine dyes appear to be spectral sensitizers (128) are better known. 

Chemical Reactions of Dyes. Decolorization is important for cyanines used ia imaging materials. Understanding decolorization provides clues to dye reactions that may cause degradation of imaging materials duting preparation and storage. For many dyes, protonation of the methine chain occurs readily and reversibly (64). Highly basic carbocyanine dyes like those from benzimidazole (eg, 36) protonate so readily that this provides a practical decolorization method. 

Many cationic dyes for acrylic fibres, especially methines, such as Cl Basic Red 13, Cl Basic Violet 7 and Cl Basic Red 74 are very bright and fluorescent and hence this fibre has a place in fluorescent textiles. 

Basic (cationic) dyes contain cationic groups which are ionized in the dyebath. They are applied to acrylics, nylon, polyester, and paper and are most often azo, anthraquinone, triarylmethane, quinoline, thiazine, methine, oxazine, and acridine types. 

With divalent metals such as Cu11, Ni11, and Co11, bidentate azo and azo-methine dyes form 1 2 metal-complexes with the basic structure 5 [1]. 

Developed in the late 1930s for acetate, methine dyes derived from Fischer s Base (2,3 -dihydro-1,3,3-trimethyl-2-methylene-1H-indole) and Fischer s Aldehyde ([1,3-dihydro-1,3,3-trimethyl-2H-indol-2-xylidene]-acetaldehyde) later found use in dyeing acrylic fibers. They provide bright yellow to violet dyeing with acceptable lightfastness. Basic Red 14 and Basic Yellow 11 are examples of this type with a delocalized charge ... 

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