Triphenylmethane dyes light-fastness

Triphenylmethane dyes comprise one of the oldest classes of synthetic dyes. They are of bdUiant hue, exhibit high tinctorial strength, are relatively inexpensive, and may be appHed to a wide range of substrates. However, they are seriously deficient in fastness properties, especially fastness to light and... 

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]. 

Chloro-2-aminophenol is used chiefly for the preparation of blue azo dyes which can be after-chromed. Its combinations with chromotropic acid and with acetyl-H acid were the purest chrome blues known before the discovery of the chroming triphenylmethane dyes (eriochrome azurol). The latter dyes are superior in depth and brilliance of color, but are not as fast to light as the azo dyes from 4-chloro.2-aminophenol and chromotropic acid or acetyl-H acid. 

The assignment of the observed fast kinetic rate to trans-cis isomerization is strongly supported by our experimental data, which show that the time constant is related to the viscosity by approximately The Forster and Hoffman modeP was developed originally to explain the Q= relationship where Q is the fluorescence quantum yield and 17 is the viscosity of the medium for triphenylmethane dyes. In addition, it was predicted that the fluorescence lifetime, r, should follow a similar relationship t = c if According to this model, absorption of light produces a vertically excited Franck-Condon state with the phenyl rings still at a ground state equilibrium... 

Triphenylmethane dyes are characterized by the resonance-stabilized chromophore shown below. They are among the strongest and brightest of synthetic dyes, but usually do not exhibit good fastness to light. An exception is found with acrylic fibers, which are dyed in bright lightfast hues by selected triphenylmethane dyes. 

This consists of the phthalocyanine dyes, an example of this group being Coomassie Turquoise Blue 3G. This is a trisulphonated derivative of copper phthalocyanine. It dyes wool a very bright greenish blue shade. Its fastness to light is better than the triphenylmethane acid dyes which alone will give comparable shades. 

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