Photochromic aminotriarylmethane solutions for flash blindness protection

Photochromic filter solutions have been developed for flash blindness protection. Triarylmethane leuconitriles, which dissociate into a colored dye cation and cyanide ion when activated by uv light, produce high closed densities and open transmission. The fading rate of the dye solutions can be controlled by the choice of solvent or bleach anion concentration. However, the closed density of these solutions decreases when repeatedly activated with a xenon flash. It has been found that this fatigue can be greatly reduced by substitution of bisulfite for cyanide as the triarylmethane counter ion. Triarylmethane bisulfite solutions retain up to 99% of the initial closed density after fifty xenon flashes. The temperature coefficient of fading of the leucobisulfites in aqueous methanol is much smaller than that of spiropyran solutions in toluene.