Used as a key intermediate in the synthesis of cyanine dyes, particularly in the production of sensitizing dyes for photographic emulsions. Its sulfonic acid groups enhance water solubility, making it suitable for aqueous-based dye formulations. Also employed in the development of optical brighteners and fluorescent probes due to its rigid aromatic structure and ability to form conjugated systems. Its derivatives find use in biomedical imaging and as markers in analytical chemistry.