ChemilumiscenceBy

Muhammad Asif shaheen

Chemiluminescence

• Chemiluminescence is the production of light from a chemicalreaction.

• Two chemicals react to form an excited (high-energy) intermediate,which breaks down releasing some of its energy as photons of light toreach its ground state

• A + B -> AB* -> Products + Light

• In the process, a packet of energy (a photon) is released in the form ofelectromagnetic radiation.

• The wavelength depends on the amount of energy. If the wavelengthis within the range of visible light, the electron transition will beperceived as light of a particular colour.

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• Chemiluminescent reactions do not usually release much heat,because energy is released as light instead.

• Luminol produces a light when it reacts with an oxidising agent.

• Chemiluminescent reactions can be grouped into three types:

• Chemical reactions using synthetic compounds are commonly termedchemiluminescent reactions.

• Light-emitting reactions arising from a living organism, such as thefirefly or jellyfish, are commonly termed bioluminescent reactions.

• Light-emitting reactions which take place by the use of electricalcurrent are designated electrochemiluminescent reactions

Mechanism of Chemiluminescence

• Chemiluminescence is the emission of light when an electron returnsfrom an excited or higher energy level to ground state energy levels

• The excitation event is caused by a chemical reaction involving theoxidation of organic compounds like luminol, isoluminol, acridinumesters and luciferin by an oxidant (hydrogen peroxide, hypochloriteand oxygen). Light is emitted in this oxidation reaction

• These reactions occur in the presence of catalysts such as enzymes(ALP, HRP) metal ions or metal complexs (Cu and Fe )..

Bioluminescence

• When fireflies glow, the luciferin is oxidised to produce an excited complex, which falls back down to the ground state, releasing a photon of light, just like the chemiluminescent reaction of luminol

• Luciferase

Luciferin + O2 → Oxyluciferin + Light

Electrochemiluminescence

• Electrochemiluminescence or electrogeneratedchemiluminescence (ECL) is a kind of luminescence produced duringelectrochemical reactions in solutions.

• In electrogenerated chemiluminescence, electrochemically generatedintermediates undergo a highly exergonic reaction to produce anelectronically excited state that then emits light upon relaxation to alower-level state. This wavelength of the emitted photon of lightcorresponds to the energy gap between these two states

Luminometer

Chemiluminescence in forensics

• Forensic scientists use the reaction of luminol to detect blood atcrime scenes. A mixture of luminol in a dilute solution of hydrogenperoxide is sprayed onto the area where the forensic scientistssuspect that there is blood. The iron present in the haem unit ofhaemoglobin in the blood acts as a catalyst in the reaction. The roommust be dark and if blood is present, a blue glow, lasting for about 30seconds, will be observed. The forensic investigators can record thisglow by using photographic film, which can be used as evidence incourt for the presence of blood at the scene