An alpha-aminoketone derivative co-initiator library for type II photoinitiating systems in free radical photopolymerization

A library of co-initiators for Type II photoinitiating system was discovered, which was characterized by alpha-aminoketone structural units. This alpha-aminoketone derivative library encompassed a broad spectrum of compounds, including peptides, glycine ester derivatives, piperazinone derivatives, piperidone derivatives, and others. When combined with camphorquinone under aerobic conditions, these co-initiators demonstrated versatile radical photopolymerization initiation capabilities across various pH conditions. Among them, 1-methyl-3-oxopiperazine demonstrated significantly superior performance compared to the benchmark ethyl 4-dimethylaminobenzoate (EDB). Moreover, 1-methyl-3-oxopiperazine demonstrated superior biocompatibility relative to EDB in L929 fibroblast assays, exhibiting minimal cytotoxicity across all tested concentrations. This optimal alpha-aminoketone derivative displayed broad compatibility with both hydrophobic and hydrophilic monomers, as well as diverse photosensitizers. Notably, when paired with camphorquinone, it effectively initiated the photopolymerization of formulations containing black pigment – a challenging condition for conventional systems – highlighting its robust reactivity and significant potential for application in advanced photocuring technologies, including dental restorative materials and biohydrogel fabrication. Static photolysis, cyclic voltammetry analysis, ESR spectroscopy, free energy calculations and computational chemistry analysis collectively elucidated the photoinitiating mechanisms.