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- For the '"Sensitiser" used in explosives see Explosive.
Sensitiser in chemoluminescence is a compound, capable of light emission after it has received energy from a molecule, which became excited previously in the chemical reaction. A good example is this:
If we mix together alkaline solution of sodium hypochlorite and a concetrated solution of hydrogen peroxide, a reaction occurs:
ClO-(aq) + H2O2(aq) › O2*(g) + 2H+(aq) + 2Cl-(aq)
O2* is excited oxygen - meaning, one or more electrons in O2 molecule have passed over to higher molecular orbitals. When they return to ground state, light is emitted. So oxygen produced by chemical reaction somehow 'absorbed' the energy released by this reaction and became excited. Now, this oxygen has to return to ground state because it is unstable if excited and that is only possible by lowering its energy. It can do that in more than one way:
- it can react further, without any light emission
- it can be converted without any emission, for example, it can give off heat OR it can transfer its energy to another molecule
- it can emit light
The intensity, duration and colour of emitted light depend on quantum and kinetical factors as well. However, excited molecules are frequently less capable of light emission in terms of brigtness and duration when compared to sensitisers. This is because sensitisers can store energy (that is, be excited) for a longer period of time than other excited molecules. The energy is stored through means of vibration, so sensitisers are usually compounds, which either include systems of aromatic rings or many double/triple bonds in their structure. So, if an excited molecule transfers its energy to sensitiser and thus makes it excited, longer and far more visible 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
"Sensitiser"