Widely used in the synthesis of cyanine dyes, particularly for near-infrared fluorescent probes applied in bioimaging and medical diagnostics. Its sulfonic acid group enhances water solubility, making it suitable for biological labeling and staining applications. Commonly employed in the development of optical sensors and photodynamic therapy agents due to its strong light absorption and emission properties. Also utilized in photographic dyes and dye-sensitized solar cells for improved light harvesting.