Dyes with Releasable Cationic Groups

Dyes with releasable cationic groups are converted to water-insoluble dyes when heated in the dye bath. They can then enter textile materials that are amenable to dyeing with disperse dyes. Using this method, for instance, it is possible to dye polyester materials without having first to generate a finely dispersed form of the colorant with the aid of surfactants. An example of such a releasable group is the isothiouronium moiety [152], Dyes with isothiouronium groups are also suitable for wool [153], 

Reaction of dyes containing a primary amino group with dimethylformamide and an inorganic acid chloride, e.g., phosphoryl chloride, permits introduction of the formamidinium group (e.g.,57), which is also scissioned off upon heating in the dye bath [154], A similar reaction occurs with the trialkylhydrazinium moiety obtained by reacting formyl-substituted azo dyes with dialkylhydrazines and subsequent quatemization [155], 

The syntheses of the numerous groups of cationic azo dyes are described under each specific group in Section 3.7.2. 

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Finding a supramolecular system capable of fast and spatially controllable release of cations upon irradiation is of great interest for the study of intracellular process triggered by an ion concentration jump [42, 43, 45-47]. The complex of metal ions with a crown ether-linked merocyanine (DCM-crown) is an example of system (Scheme 7.9) which can temporarily release ions [46]. DCM-crown consists of DCM, a well-known laser dye, in which the dimethylamino group has been replaced by a macrocycle (monoaza-15-crown-5) that can bind metal ions [42]. 

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