Dyes with Localized Charge

1) AzoDyes. The localized charge in cationic azo dyes may reside either in the diazo moiety (e.g., 19) [15] or in the coupling component (e g., 20) [16]  

---

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. 

In avian, mammalian and amphibian embryos, PG molecules, chiefly CS-PG, have been localized with positively charged dyes, such as alcian blue (Pintar, 1978 Derby, 1978 Erickson and Weston, 1983 Tucker, 1986) and ruthenium red (Hay,... 

Examples of the third type of cationic dye, with a localized pendant charge, are Basic Red 18 and Basic Blue 21 ... 

Basic Red 18 (131), Basacryl Red X-NL [14097-03-17 is an example of a pendant cationic azo dye, ia which a localized positive charge is not conjugated with the chromophoric system. /V-Kthy1-/V-(2-ch1oroethy1)ani1ine [92-49-9] reacts with trimethyl amine to form the ammonium salt coupler. The diazo component ia Basic Red 18 is 2-ch1oro-4-nitroani1ine [121 -87-9]. 

The most efficient factor in stabilizing the electronic state is the dipole-dipole interaction. This creates a local electric field (reactive field) around the excited dye interacting with its dipole [14]. If the charges are present in its vicinity, they create an electric field that interacts with the dye dipole and induces electrochromic shifts of absorption and fluorescence spectra. The direction of these shifts depends on the relative orientation of the electric field vector and the dye dipole. These effects of electrochromism are overviewed in [15]. 

---