Synthesis and evaluation of novel photochromic disazo condensation pigments

Photochromic disazo condensation pigments have been synthesized by the cond ensation of 1-azaphenyl mercuric acetate-2-hydroxy-3-naphthoic acid with va rious benzidine derivatives and subsequent: treatment dithizone. The photoc hromic disazo condensation pigments have been characterized by their IR spe ctra and elemental analysis. The kinetic study of photochromic behaviour ha s been investigated by preparing films of the pigment. The pigment film on exposure to sunlight or tungsten light source of suitable wavelength showed very good photochromic effect. The film regained its original colour on re moval from sunlight. The duration for return of the colour depends upon the intensity of incident light, ambient temperature, moisture content and the rmal treatment of the film.