Used as a fluorescent probe in biological imaging due to its ability to enter cells and emit strong fluorescence upon hydrolysis. Commonly applied in viability assays to distinguish live and dead cells, where intact cell membranes prevent entry, while damaged membranes allow uptake and retention of the dye. Also utilized in photodynamic therapy research as a photosensitizer that generates reactive oxygen species when exposed to light, enabling targeted cell destruction. Employed in ophthalmic diagnostics to detect corneal abrasions and epithelial defects by staining damaged tissue. Its lactone form offers improved stability and membrane permeability compared to the charged form, making it suitable for intracellular applications.