Subtle ligand effects in oxidative photocatalysis with iridium complexes: application to photopolymerization.

Iridium(III) complexes were designed and evaluated as efficient photoinitiators of polymerization reactions in combination with iodonium salts and silanes. Mechanistically, these reactions were shown to proceed through oxidative photoredox catalysis, generating aryl and silyl radicals under very soft irradiation conditions (blue LED, xenon lamp, and even sunlight). These radicals can initiate the free radical polymerization of acrylates or can be oxidized during the catalytic cycle to promote the ring-opening polymerization of epoxy monomers.

A novel photopolymerization initiating system based on an iridium complex photocatalyst.

The use of a photocatalyst (tris(2-phenylpyridine)iridium [Ir(ppy)(3)]) being able to generate both radicals and cations to initiate free radical polymerization and ring opening polymerization is presented. Remarkably, under soft irradiations (fluorescence bulb, sunlight), excellent cationic polymerization profiles and final conversions are obtained. The involved mechanisms are investigated by ESR experiments.