Used as a spin label in electron paramagnetic resonance (EPR) spectroscopy to study molecular dynamics and structural changes in proteins, membranes, and polymers. Its stable radical allows real-time monitoring of local viscosity, polarity, and conformational changes. Commonly applied in biochemical assays to probe protein folding, ligand binding, and membrane fluidity. Also utilized in polymer science to investigate cross-linking, degradation, and phase behavior due to its sensitivity to environmental changes.