Espiro - benzopirano and espiro - naftopirano fotocromico, espiro - Piran fotocromico, espiro - naftopirano heliocromico, espiro - Piran heliocromico, lens and flat or oftalmica process of rearrangement of Caisen

摘要

A series of novel photochromic spiropyrans are disclosed in which a spiro-adamantane group is introduced into the 2-position of the benzopyran or naphthopyran ring. The spiropyran compounds of the invention exhibit heliochromic properties, i.e. they colour in sunlight and fade rapidly at ambient temperatures in the absence of U.V. light, making them good candidates for use in the manufacture of sunglasses. The invention includes lenses which darken in sunlight and incorporate the novel spiropyrans and a process for the preparation of the spiropyran compounds.