Iridium Photocatalysts
in Free Radical Photopolymerization
under Visible Lights
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Abstract
A series of iridium(III) complexes was designed and investigated
as new potential photocatalysts for radical polymerization reactions.
The photocatalytic reduction cycle involves the combination of an
iridium complex with an amine (e.g., <i>N</i>-methyldiethanolamine)
and an alkyl halide (e.g., phenacylbromide). The different three-component
systems herein investigated are very attractive for acrylate polymerization
upon visible light irradiation. They are much more reactive than those
based on Ru(bpy)<sub>3</sub><sup>2+</sup>. Free radicals generated
during the reaction were investigated by ESR spectroscopy and the
chemical mechanisms are discussed. The crucial role played by the
photocatalyst (reduction ability and excited state lifetime) is also
demonstrated