Fluorescein isothiocyanate
Other names	FITC
Identifiers
CAS number	27072-45-3 Y
PubChem	18730
MeSH	Fluorescein-5-isothiocyanate
SMILES	C1=CC2=C(C=C1N=C=S)C(=O) OC23C4=C(C=C(C=C4)O)OC5=C3C=CC(=C5)O
Properties
Molecular formula	C21H11NO5S
Molar mass	389.382
Melting point	359.5 °C
Y (what is this?)  (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Fluorescein isothiocyanate (FITC) is a derivative of fluorescein used in wide-ranging applications including flow cytometry. FITC is the original fluorescein molecule functionalized with an isothiocyanate reactive group (-N=C=S), replacing a hydrogen atom on the bottom ring of the structure. This derivative is reactive towards nucleophiles including amine and sulfhydryl groups on proteins.

A succinimidyl-ester functional group attached to the fluorescein core, creating NHS-fluorescein, forms another common amine reactive derivative that has much greater specificity toward primary amines in the presence of other nucleophiles.

FITC has excitation and emission wavelengths of approximately 495 nm/521 nm. Like most fluorochromes, it is prone to photobleaching. Because of the problem with photobleaching, derivatives of fluorescein such as Alexa 488 and DyLight 488 have been tailored for various chemical and biological applications where greater photostability, higher fluorescence intensity, or different attachment groups are needed.