2. INTRODUCTION
• Oxidation under the influence of the light or radiant energy.
• Formation of radicals that induces oxidation of the material.
• Excited singlet or triplet states .
3. Photosensitiser
• This is especially useful in providing a new group of
potentially new reactive molecules.
• Aldehydes and ketones
Requirements of photosensitiser
1. It must be excited by the irradiation used.
2. Present in sufficient concentration and absorb more strongly
than the other reactants so that it is the major light absorber.
3. Energy of triplet state of sensitiser must be greater than that
of the reactant.
4. Must be able to transmit energy to reactant.
9. 1. Formation of peroxy compound.
• Irradiating the parent organic compound in the
presence of oxygen and a sensitizer.
• Reaction occurs by the excitation of the sensitizer to
its triplet state.
• Either the triplet abstracts a hydrogen atom from the
substrate to form a radical which then reacts with
oxygen, or it interact with the oxygen molecule.
18. 6. Photo-oxidation of polymers
• Light is absorbed by a polymer - photochemical reactions can
occur as a result of activation of a polymer macromolecule to
its excited singlet or triplet states.
• Chemical change that reduces the polymer's molecular weight.
