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Fluorescein

Athanor · official

C20H12O5 · 332.3 g/mol

IUPAC name: 3',6'-dihydroxyspiro[2-benzofuran-3,9'-xanthene]-1-one

Also called FITC parent, resorcinolphthalein, uranine, fluorescent tracer

ReagentsRings
Open in Athanor
The structure of Fluorescein
Drawn from its SMILES with RDKit
Harmful or irritantWarningHarmful if swallowed · Causes serious eye irritation

Names and identifiers

IUPAC name
3',6'-dihydroxyspiro[2-benzofuran-3,9'-xanthene]-1-one
Synonyms
FITC parent, resorcinolphthalein, uranine
+ 39 more

fluorescent tracer, Solvent Yellow 94, Resorcinolphthalein, Yellow fluorescein, Fluoresceine, Fluorescein acid, 3,6-Fluorandiol, D&C Yellow No. 7, 3',6'-Dihydroxyfluoran, Japan Yellow 201, D and C Yellow No. 7, C.I. Solvent Yellow 94, Soap Yellow F, Hidacid fluorescein, Yellow 7, Fluoreszein, Fluorescein Red, D+C Yellow No. 7, 11712 Yellow, CHEBI:31624, Japan Yellow No. 201, Zlut kysela 73, 3',6'-Fluorandiol, Ki201, NSC-667256, 9-(o-Carboxyphenyl)-6-hydroxy-3-isoxanthenone, DTXSID0038887, Spiro[isobenzofuran-1(3H),9'-[9H]xanthen]-3-one, 3',6'-dihydroxy-, 9-(o-Carboxyphenyl)-6-hydroxy-3H-xanthen-3-one, TPY09G7XIR, CI 45350:1, C.I. 45350:1, NSC-759114, DTXCID8018887, 3,6-Dihydroxyspiro(xanthene-9,3'-phthalide), 3',6'-Dihydroxyspiro(isobenzofuran-1(3H),9'(9H)-xanthen)-3-one, Spiro(isobenzofuran-1(3H),9'-(9H)xanthen)-3-one, 3',6'-dihydroxy-, D & C YELLOW NO. 7 K7133, 3,6-Dihydroxyspiro[xanthene-9,3'-phthalide]

Molecular formula
C20H12O5
Empirical formula
C20H12O5
Molecular weight
332.3 g/mol
Exact mass
332.06847
CAS number
2321-07-5
PubChem CID
16850
Canonical SMILES
C1=CC=C2C(=C1)C(=O)OC23C4=C(C=C(C=C4)O)OC5=C3C=CC(=C5)O
Isomeric SMILES
C1=CC=C2C(=C1)C(=O)OC23C4=C(C=C(C=C4)O)OC5=C3C=CC(=C5)O
InChI
InChI=1S/C20H12O5/c21-11-5-7-15-17(9-11)24-18-10-12(22)6-8-16(18)20(15)14-4-2-1-3-13(14)19(23)25-20/h1-10,21-22H
InChIKey
GNBHRKFJIUUOQI-UHFFFAOYSA-N
Molfile

Names, InChI and the identifiers from PubChem, retrieved 2026-10-14.

Physical properties

TemperaturePressureDensity
Appearance
Red, orthorhombic prisms[2]
3 values

From Hazardous Substances Data Bank (HSDB), the most authoritative source here.

ValueAs writtenSource
–Fluorescein appears as yellow amorphous solid or orange-red crystals. Latter have greenish-yellow fluorescence by reflected light. Insoluble in water. Soluble in dilute aqueous bases. Very dilute alkaline solutions exhibit intense, greenish-yellow fluorescence by reflected light. Low toxicity. May be sensitive to prolonged exposure to light.[1] CAMEO Chemicals
–shownRed, orthorhombic prisms[2] Hazardous Substances Data Bank (HSDB)cites SRI Consulting, 2010 Directory of Chemical Producers. Menlo Park, CA. 2010, p. 3-258
–Orange-red, crystalline powder[2] Hazardous Substances Data Bank (HSDB)cites Lewis, R.J. Sr.; Hawley's Condensed Chemical Dictionary 15th Edition. John Wiley & Sons, Inc. New York, NY 2007., p. 572
Melting point
315 °C (decomposes)[2]
Solubility in water
In water, 50 mg/L at 20 °C[2]
3 values

From Hazardous Substances Data Bank (HSDB), the most authoritative source here.

ValueAs writtenSource
–Insoluble (NTP, 1992)[1] CAMEO Chemicalscites National Toxicology Program, Institute of Environmental Health Sciences, National Institutes of Health (NTP). 1992. National Toxicology Program Chemical Repository Database. Research Triangle Park, North Carolina.
–Slightly soluble in ethanol, diethyl ether; very soluble in acetone; soluble in pyridine, methanol[2] Hazardous Substances Data Bank (HSDB)cites SRI Consulting, 2010 Directory of Chemical Producers. Menlo Park, CA. 2010, p. 3-258
–shownIn water, 50 mg/L at 20 °C[2] Hazardous Substances Data Bank (HSDB)cites Dehn WM; J Amer Chem Soc 39: 1399-404 (1917)

Each value as its source reports it, with the source's number after it (listed under References). Where several sources report a property, the row shows the value most of them agree on, the rule the app uses; open the values to see every one.

Calculated

Heavy atoms
25
Rings
5
Aromatic rings
3
Fraction sp³ carbons (Fsp3)
0.05
H-bond donors
2
H-bond acceptors
5
Rotatable bonds
0
TPSA (Ų)
76
Formal charge
0
XLogP3
3.4 PubChem
Complexity
522 PubChem
Stereocenters
None
Double-bond geometry
None specified
Point group
Cs of one 3D conformer with its hydrogens, by Athanor’s engine (as in the app)

Elemental analysis

  • C72.29%
  • H3.64%
  • O24.07%

Isotope pattern

100%332.06822%333.0723.3%334.075335.077

Each peak is a nominal mass with its abundance-weighted exact mass, as a percentage of the tallest, from IUPAC natural isotope abundances.

Computed from the structure with RDKit 2026.09 when this page was built, beside PubChem's own computed values from its record; where the two differ, both are shown.

Predicted

log P
3.67 Crippen (Wildman and Crippen 1999)
log S (water solubility)
-4.74 ESOL (Delaney 2004), log mol/L
Synthetic accessibility
2.96 SA score, 1 easy to 10 hard (Ertl and Schuffenhauer 2009)

Drug-likeness: Lipinski’s rule of five

  • Molecular weight ≤ 500: 332.31
  • log P ≤ 5 (Crippen): 3.67
  • H-bond donors ≤ 5: 2
  • H-bond acceptors ≤ 10: 5

Passes all four rules.

¹³C NMR shifts, predicted

Predictions, not measurements; each names its method. A measured log P, where a source reports one, is under Physical properties.

Safety

Warning

Most widely reported: 383 company reports to ECHA. Source [3].

  • Harmful or irritant
  • H302Harmful if swallowed (13.6% of reports)
  • H319Causes serious eye irritation (96.6% of reports)

Precautionary statements: P264, P264+P265, P270, P280, P301+P317, P305+P351+P338, P330, P337+P317, P501

View all classifications (2)
  • [3] European Chemicals Agency (ECHA)This chemical does not meet GHS hazard criteria for 3.4% (13 of 383) of reports.
  • [3] European Chemicals Agency (ECHA) · 383 reports · WarningH302, H319

First aid

  • Eyes: First check the victim for contact lenses and remove if present. Flush victim's eyes with water or normal saline solution for 20 to 30 minutes while simultaneously calling a hospital or poison control center. Do not put any ointments, oils, or medication in the victim's eyes without specific instructions from a physician. Immediately transport the victim after flushing eyes to a hospital even if no symptoms (such as redness or irritation) develop. Skin: Immediately flood affected skin with water while removing and isolating all contaminated clothing.[1]

Safety data sheets on the supplier’s page: abcr GmbH, LGC Standards, Thermo Fisher Scientific.

Always read the supplier’s safety data sheet before working with it.

Spectra

Experimental spectra held by these sources; each link opens the source's own record.

Literature

Reading PubChem, OpenAlex and GSRS…

Bioactivity

Reading ChEMBL…

References

  1. [1]CAMEO Chemicals · Public domain (NOAA) · via PubChem · retrieved 2026-10-14
  2. [2]Hazardous Substances Data Bank (HSDB) · Public domain (US NLM) · via PubChem · retrieved 2026-10-14
  3. [3]European Chemicals Agency (ECHA) · ECHA legal notice: reuse with acknowledgement · via PubChem · retrieved 2026-10-14
  4. [4]NMRShiftDB · Linked only · via PubChem · retrieved 2026-10-14
  5. [5]Human Metabolome Database (HMDB) · Linked only · via PubChem · retrieved 2026-10-14
  6. [6]SpectraBase · Linked only · via PubChem · retrieved 2026-10-14
  7. [7]MassBank of North America (MoNA) · CC BY 4.0 · via PubChem · retrieved 2026-10-14
  8. [8]NIST Mass Spectrometry Data Center · Linked only · via PubChem · retrieved 2026-10-14
  9. [9]MassBank Europe · Linked only · via PubChem · retrieved 2026-10-14
  10. ·Calculated values: computed by Athanor with RDKit 2026.09 from the structure.
  11. ·Literature on PubChem

Data last updated 2026-10-14.