Used as a key intermediate in the synthesis of photochromic compounds, especially in the production of dyes and pigments that change color when exposed to UV light. Commonly applied in the development of photochromic lenses for eyewear, where it contributes to light-sensitive properties that enable automatic tint adjustment. Also utilized in specialty inks and coatings for security printing and optical switches due to its reversible color response. Its carboxylic acid functionality allows for chemical modification and attachment to polymers, enhancing durability and performance in solid-state applications.