Used as an active ester reagent in bioconjugation processes, particularly for labeling proteins and peptides with fluorescent dyes, biotin, or other functional groups. The N-succinimidyl ester reacts selectively with primary amines (such as lysine residues) under mild aqueous conditions to attach the 4-fluorobenzoate group, forming stable amide bonds. Its high reactivity and good solubility in organic and aqueous-organic solvents make it suitable for modifying biomolecules in research and diagnostic applications. Notably, the para-fluoro substituent enables subsequent nucleophilic substitution with Fluorine-18 for the preparation of PET imaging probes. Commonly employed in the development of immunoassays, targeted drug delivery systems, and molecular imaging agents.