Iridium Photocatalysts in Free Radical Photopolymerization under Visible Lights

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., N-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)(3)(2+). 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.