science expo: CHEMILUMINESCENCE

Chemiluminescence (sometimes "chemoluminescence") is the emission of light (luminescence) with limited emission of heat as the result of a chemical reaction. Given reactants A and B, with an excited intermediate ◊, we have:

[A] + [B] → [◊] → [Products] + light

For example, if [A] is luminol and [B] is hydrogen peroxide in the presence of a suitable catalyst we have:

luminol + H₂O₂ → 3-APA[◊] → 3-APA + light

where:

• where 3-APA is 3-aminophthalate
• 3-APA[◊] is the excited state fluorescing as it decays to a lower energy level.

The decay of the excited state[◊] to a lower energy level is responsible for the emission of light. In theory, one photon of light should be given off for each molecule of reactant, or Avogadro's number of photons per mole. In actual practice, non-enzymatic reactions seldom exceed 1% Q_C, quantum efficiency.

A standard example of chemiluminescence in the laboratory setting is found in the luminol test, where evidence of blood is taken when the sample glows upon contact with iron. When chemiluminescence takes place in living organisms, the phenomenon is called bioluminescence. A lightstick emits light by chemiluminescence.