PHOTOCHROMIC MATERIALS FOR DATA STORAGE AND DISPLAY.

Studies on the mechanism of photochromism of salicylidene anilines indicate that the currently accepted mechanism involving hydrogen transfer and geometrical isomerism may not be correct. Photochromism was observed under conditions in which the postulated hydrogen transfer cannot occur. Contrary to reports in the literature, polyhalogenation of the aniline ring does not inhibit photochromism, although polyhalogenation of the salicylidene ring apparently does. A number of substituted salicylidene anilines were prepared. Data are given on methods of preparation and properties of salicylidene anilines containing fluorine, chlorine, bromine, as well as hydroxy and carboxy groups. Absorption spectra for the yellow and red forms of representative compounds are included. A number of examples of polymorphic salicylidene anilines were included. A number of examples of polymorphic salicylidene anilines were investigated transitions between crystalline forms both in the solid state and in the presence of solvents were observed. Data are reported on the wavelengths causing the photochromic changes. Data were obtained on the energy requirements for changing alpha1-salicylidene aniline from yellow to red using the most effective wavelength, 380 millimicrons. Starting with the anil in the yellow state, an increase of 0.1 in absorbance at 475 millimicrons requires about 0.04 joule per sq cm. However, more energy is required at higher levels of absorbance. Author