Basic dyes light fastness

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. 

Derivatives of triphenylmethane were among the earliest synthetic colorants, and are still in demand where bright, intense colours are needed without the necessity for outstanding fastness to light and chemical reagents. Basic dyes of this type, as well as other cationic dyes, are suitable for dyeing conventional acrylic fibres, on which they show better fastness properties than on natural fibres. The photodegradation of triphenylmethane dyes has been reviewed [42]. 

Of some importance as textile dyes are aza analogues of polymethine (cyanine) dyes. Azacarbocyanines result when Fischer s aldehyde is heated with primary aromatic amines. Thus Cl Basic Yellow 11 (6.220) is obtained when Fischer s aldehyde is condensed with 2,4-dimethoxyaniline. The equivalent reaction with 2-methylindoline gives Cl Basic Yellow 21 (6.221), which has superior light fastness but has been classified by ETAD as toxic [73]. The tinctorially strong golden yellow diazacarbocyanine dye Cl Basic Yellow 28 (6.222) is prepared by coupling diazotised p-anisidine with Fischer s base (6.223), followed by quaternisation with dimethyl sulphate. Some triazacarbocyanine dyes are also used commercially. 

Cationic (Basic) Dyes. These water-soluble cationic dyes are applied to paper, polyacrylonitrile (e g. Dralon), modified nylons, and modified polyesters. Their original use was for silk, wool, and tannin-mordanted cotton when brightness of shade was more important than fastness to light and washing. Basic dyes are water-soluble and yield colored cations in solution. For this reason they are frequently referred to as cationic dyes. The principal chemical classes are diazahemi-cyanine, triarylmethane, cyanine, hemicyanine, thiazine, oxazine, and acridine. Some basic dyes show biological activity and are used in medicine as antiseptics. 

The basic dyes are of poor fastness to light and vary with regard to washing fastness from poor to moderate. Some examples on wool are tabulated. below to provide general conception of their fastnesses. 

Modified Basic Dyes. In comparison say with dyeings on cotton, the light fastness rises dramatically when these dyes are used on PAC fibres. 

Fluorescence Gel Films. Fluorescent dyes are used in the sol-gel process for monitoring gelation process (McKieman, 1989 Pouxviel, 1989) but there are little basic data for fluorescence gel film. In this sechon, ophcal properties such as fluorescence spectra, fluorescence quantum yield and fluorescence lifetime, and light fastness ofthe fluorescent gel films formed by the sol-gel method using organic dyes and pigments to show emission of three colors, blue, green and red, are described. 

The parent molecule of aromatic azo compounds is azobenzene, whose UVATIS spectroscopic features and photochemistry are basically determined by the azo group -N = N- in conjugation with two phenyl substituents. The most important applications of azobenzene derivatives (azobenzenes) are their use as dyestuffs. Azo dyes absorb visible light and generally show remarkable light-fastness, which is due to an effective deactivation mechanism of the excited-state molecules that includes photoisomerization. ZoUinger has discussed this aspect from the viewpoint of dyestuff chemistry. 

Like most ammonium bases, methylene blue does not dye wool easily, but is readily fixed on silk and tannined cotton. It has also a slight affinity for unmordanted vegetable fibres. Methylene blue is principally used in cotton-dyeing. It dyes a greenish shade of blue, which shows a dull tone similar to that of indigo. It is very fast to light, and the shades may be readily modified by other basic dyestuffs, such as methyl violet or malachite-green. 

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