Used primarily as an intermediate in the synthesis of photochromic dyes, especially in the production of ophthalmic lenses that darken upon exposure to UV light. It plays a key role in the development of high-performance photochromic materials due to its ability to form stable, reversible ring-closed structures when exposed to sunlight. Also utilized in specialty polymers and light-sensitive coatings where controlled color change is required. Its derivatives are found in advanced optical devices and smart windows.