Chemiluminescence

A chemoluminescent reaction carried out in an erlenmeyer flask producing a large amount of light.

Chemiluminescence (or Chemoluminescence) is a kind of luminescence and is a process of making light from a chemical reaction. The light made in chemiluminiscence is not directly related to heat. A simple two step example of a reaction of A, and B, that produces; C, D, and Light.

[A] + [B] → [C*] + [D]

[C*] → [C] + [Light(hν)]

Where C* is an excited state of C. This reaction is simpler than most chemiluminesence reactions. The excited state in chemiluminescence happens when electrons in higher orbitals are made from a chemical reaction. The excited state is less stable (higher in energy) than the ground state, this causes the electrons in the excited state to fall to the ground state(lower energy). The excited state is normally not stable because it is higher in energy, to become more stable the electron drops to the ground state, this extra energy between the two states is radiated in the from of light. Chemiluminescence in biological systems and is also named bioluminescence. The amount of measurable light made is called Radiant Intensity, I_CL(photons emitted per second) and is a term used to place a number value on the observed results. The Radiant Intensity is related the rate of the reaction and the Quantum Yield(photons per molecule reacted).

Analytical applications

The device needed to measure the light made is simple and needs; something to hold the sample, and a photomultiplier tube. There are three ways for this to be used in chemical measurements; sometimes the product wanted makes light when it reacts with another compound, in another type the amount of light made drops when the wanted product is added, and an sometimes the wanted product when added to a chemiluminescence reaction makes more light(a catalytic reaction).

Analysis of gases

The method was made because it can measure small amounts of compound that are atmospheric pollutants. one of the most used methods measures the amount of nitrogen monoxide by reacting it with ozone. The light made has a wavelength range of 600 to 2800 nm.

Analysis of liquids

Luminol is the most well known type of compound used for chemiluminescence in liquids.

Analysis of cellular species

Ca2+(calcium) inside of different parts of cells like the mitochondria can make light when it reacts with a protein from jellyfish named aequorin. Nitric oxide(NO) is in cells and is a way for cells to talk to each other, this can be measured with the compound luminol.

Common uses

• Glowsticks

Other examples

A complex example of chemiluminescence involving organic species 2-bromohydroperoxide in the presence of a base, intermediate 3,3,4,4-tetramethyl-1,2-dioxacyclobutane (a 1,2-dioxetane) is produced, heat is then applied to produce the product acetone and light.

An example of chemiluminescence molecules in nature is firefly luciferin.

References

• Daniel C. Harris. In Quantitative Chemical Analysis Seventh Edition: 2007 by W.H. Freeman and Company.
• Douglas A. Skoog, James F. Holler, Stanley R. Crouch. In Principles of Instrumental Analysis Sixth Edition:2005 by Thomson, Brooks, Cole.