Pinacyanol chloride is primarily used as a biological stain in microscopy, particularly for enhancing the visibility of cellular components under a microscope. It is effective in staining mitochondria and other organelles, aiding researchers in studying cell structure and function. Additionally, it has been utilized in the field of photodynamic therapy due to its light-sensitive properties, where it can generate reactive oxygen species to target and destroy abnormal cells. In material science, pinacyanol chloride is employed as a sensitizer in photographic films and as a dye in various optical applications, leveraging its ability to absorb and emit light at specific wavelengths. Its unique properties make it a versatile compound in both biological and industrial research.