Hexacyanine 2 is primarily utilized in the field of photodynamic therapy (PDT) due to its strong light-absorbing properties. It acts as a photosensitizer, which, when exposed to specific wavelengths of light, generates reactive oxygen species that can destroy targeted cells, such as cancer cells. This makes it a valuable tool in treating various types of tumors. Additionally, it is employed in bioimaging and diagnostic applications, where its fluorescence properties help in visualizing cellular structures and processes. Its ability to bind to specific biomolecules also aids in studying molecular interactions and dynamics in biological systems.