Fluorescent Dye

Liquid light is prepared!

Scientific name: A way to synthesize a high fluorescent substance is demonstrated.


How to Make Fluorescein (Fluorescent Dye)

by NurdRage

Make Fluorescein

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Fluorescent Water (Fluorescein)

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Fluorescein and related xanthene dyes

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Wear eye protection goggles and gloves. Perform synthesis only in a fume hood. Be careful handling concentrated sulfuric acid.

Always follow general safety recommendations. Please note that conducting chemistry experiments you must comply with the relevant legal procedures in your country.

Reaction formula

2 C6H6O2 + C6H4(CO)2O -[toC + H2SO4]→ C20H12O5 + 2H2O

Step-by-step instruction

WARNING! This experiment is dangerous! You should NOT perform this at home. ONLY carry out this experiment, if you are a trained chemist, and you understand local safety and legal requirements, which are required to perform such experiments

  1. Perform this experiment outside or in a fume hood. Wear gloves.
  2. To obtain fluorescein you need to prepare 166 mg of phallic anhydride and 220 mg of resorcinol.
  3. Place the chemicals into a small beaker.
  4. Add 3 drops of concentrated sulfuric acid.
  5. Stirring the substances with a thin glass rod heat the beaker gently until the mixture turns dark red. Keep heating at about 200°C for a 5 min. Then turn off heating and let the product cool down to room temperature.
  6. To prepare concentrated water solution of fluorescein, add about 10 ml of water into the beaker.
  7. Since fluorescein is not very soluble in water I at neutral pH add about 300 mg of sodium hydroxide.
  8. To test fluorescent properties of synthesized substance turn on a source of ultraviolet light and put a few drops of the obtained solution into a large beaker filled with water.
  9. Glowing yellow-green waves spread along the solute.

Scientific background

Phallic anhydride and resorcinol react producing fluorescein. This reaction relates to the Fridel-Crafts reactions set proceeding by electrophilic aromatic substitution. The sulfuric acid plays a role of a catalyst for this reaction. Also zinc chloride is suitable for this purpose. Von Bayer was the first who discovered this method of fluorescein preparation in 1871. Now fluorescein is one of the most common fluorescent probes. It is a highly fluorescent molecule that adsorbs light at 492 nm and emits it at 517 nm in water. Large fluorescence quantum yield and high photostability makes it a very useful fluorescent label. Quantum yield characterizes the efficiency of fluorescence process. It is the ratio between the numbers of emitted and adsorbed photons. The fluorescein quantum yield is 0.92. It means that 92% of the photons adsorbed results in photons emitted.


Published on 09 September 2015

  • Fire
  • Heating with fire
  • Explosion
  • Poisoned gas
  • Organic
  • Electricity
  • Solution
  • Oxidation reduction
  • Color change
  • Precipitate
  • Gassing
  • Catalyst