Widely used as a fluorescent pH indicator in biological and analytical applications, this compound is particularly effective in intracellular pH measurements due to its high sensitivity and reversible protonation response. Its fluorescence intensity changes significantly across the physiological pH range, making it valuable in microscopy and flow cytometry for monitoring cellular acidification or alkalization. The compound is also employed in sensor systems where real-time pH monitoring is required, including in microfluidic devices and biosensors. Its spirocyclic structure provides stability and reduces leakage from cells, enhancing its utility in live-cell imaging. Additionally, it serves as a key component in dye mixtures for multicolor labeling and in calibrating fluorescence-based instruments.