5-TRITC is an amine-reactive fluorescent dye commonly used to label proteins and nucleic acids. It reacts with amino groups in proteins to form stable thioether bonds, thereby labeling and detecting the presence and localization of specific proteins, producing bright red-orange fluorescence with excitation/emission maxima of about 555/580 nm.

5-TRITC (also named G isomer), a purified single isomer of the 5(6)-TRITC mixed isomers, is predominantly used in the label of peptides and proteins.