- Sensitiser
A sensitiser in
chemoluminescence is a chemical compound, capable oflight emission after it has received energy from a molecule, which became excited previously in the chemical reaction. A good example is this:When an alkaline solution of
sodium hypochlorite and a concentrated solution ofhydrogen peroxide are mixed, a reaction occurs::ClO-(aq) + H2O2(aq) → O2*(g) + H+(aq) + Cl-(aq) + OH-(aq)
O2* is excited oxygen - meaning, one or more electrons in the O2 molecule have been promoted to higher-energy
molecular orbital s. Hence, oxygen produced by this chemical reaction somehow 'absorbed' the energy released by the reaction and became excited. This energy state is unstable, therefore it will return to theground state by lowering its energy. It can do that in more than one way:* it can react further, without any light emission
* it can lose energy without emission, for example, giving off heat to the surroundings or transferring energy to another molecule
* it can emit lightThe intensity, duration and colour of emitted light depend on quantum and kinetical factors. However, excited molecules are frequently less capable of light emission in terms of brightness and duration when compared to sensitisers. This is because sensitisers can store energy (that is, be excited) for longer periods of time than other excited molecules. The energy is stored through means of
quantum vibration , so sensitisers are usually compounds which either include systems of aromatic rings or many conjugated double and triple bonds in their structure. Hence, if an excited molecule transfers its energy to a sensitiser thus exciting it, longer and easier to quantify light emission is often observed.The colour (that is, the
wavelength ), brightness and duration of emission depend upon the sensitiser used. Usually, for a certain chemical reaction, many different sensitisers can be used.List of some common sensitisers
*
Violanthrone
*Isoviolanthrone
* Fluoresceine
*Rubrene
*9,10-diphenylanthracene
*Tetracene
*13,13'-dibenzantronile
Wikimedia Foundation. 2010.
