Naphthoquinone-imidazolyl derivatives-based oxime esters as photoinitiators for blue LED-induced free radical photopolymerization

In this study, we report the successful design and synthesis of nine novel oxime esters based on the naphthoquinone-imidazolyl scaffold and serving as photoinitiators to trigger photopolymerization processes under visible light. In the presence of acrylate monomers and upon irradiation at 405 nm with a LED, these photoinitiators showed remarkable photoinitiating abilities. Newly developed photoinitiators exhibited a multifunctional photoinitiating ability since these structures could act both as Type I photoinitiators or in multicomponent systems, with an improvement of the monomer conversions in the second case. This performance enhancement was notably evidenced in two-component systems comprising the new compounds in combination with either an iodonium salt or an amine. This enhancement of the monomer conversion can be assigned to favorable interactions between the dyes and the different additives, enabling to improve the free radical generation. The underlying chemical mechanisms that govern the radical chemistry during the different photopolymerization processes were explored through a series of systematic experiments. To end, usefulness of these photoinitiators was confirmed by the successful production of 3D objects using the Direct Laser Write method. This suggests promising applications of these photoinitiators in 3D printing technologies.