Dyes with Delocalized Charge

Cationic dyes with delocalized charge are classified with the methine dyes (see Section 2.6). They may be viewed as vinylogous amidinium salts 3 [1]  

All of these dyes can be represented by various resonance formulas. They are characterized by high color strength. 

Dyes in which both charged terminal atoms are not part of a heterocyclic ring are called streptocyanine dyes. An example is 4, which dyes paper in a greenish yellow shade [2], 

In the hemicyanine dyes, one of the charged terminal atoms is part of a heterocyclic ring, and the other is a nitrogen atom directly linked to the methine chain (5). 

An example of this type is the enamine dye 6, which confers a yellow color to polyacrylonitrile fibers [3], 

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The cyanine class of symmetrical dyes with delocalized positive charges was originally introduced by Alan Waggoner and has provided extraordinarily... 

Dyeing Mechanism. The original basic dyes were characterized by a delocalized charge in the molecule. As the importance of acryHc fibers grew basic dyes were developed with localized charge in one specific part of the molecule allowing stronger salt links to be formed than with the delocalized type. 

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 ... 

So-called delocalized cationic azo dyes are another type ia which the positive charge is delocalized (or distributed) across the dye cation. Basic Blue 54 (132) (2-amiao-6-methoxybenzothiazole coupled to /V, /V-dimethy1 ani1 ine and then quarternized with dimethyl sulfate) is an example of this class which can also be considered as a diazamethine dye. 

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