Used in the synthesis of cyanine dyes, particularly for photographic sensitizers and biological staining. Its sulfonic acid group enhances water solubility, making it suitable for applications in aqueous environments such as in histology and microscopy. Also employed in the development of optical sensors and fluorescent probes due to its ability to form conjugated systems with strong absorption in the visible range. Additionally, derivatives are explored in dye-sensitized solar cells for light harvesting.