Diphenyl functional porphyrins and their metal complexes as visible-light photoinitiators for free-radical, cationic and thiol–ene polymerizations

This investigation demonstrates the excellent photoinitiating properties of novel visible-light absorbing diphenylporphyrins (DPPs) for free-radical (FRP), cationic (CP) and thiol–ene polymerizations under visible LED irradiation (405 and 530 nm) at low intensities, under air or in laminate. Kinetics results on FRP and CP showed that DPPs are much more efficient photoinitiators than common Type II photosensitizers, i.e. camphorquinone or benzophenone. As confirmed by EPR and laser flash photolysis studies, DPPs play a dual role as an electron donor and in the H-abstraction reaction when combined with iodonium salt (Iod), N-methyldiethanol amine (MDEA) or thiol derivative, respectively.