Naphthoquinone-based imidazolyl esters as blue-light-sensitive Type I photoinitiators

In this work, a series of Type I photoinitiators (PIs), based on the naphthoquinone scaffold, were designed and synthesized for the first time in order to induce photopolymerization under visible light. As a result, these PIs exhibit excellent photoinitiation abilities in the presence of acrylate monomers upon LED@405 or @455 nm irradiation. Interestingly, some compounds have better photoinitiation performance than the benchmark Type I phosphine-oxide, i.e. diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO) upon exposure to LED@455 nm. Chemical mechanisms supporting the photopolymerization process were investigated through different techniques as well as theoretical calculations. In addition, the newly proposed structures were also investigated in two-component photoinitiating systems and exhibited a higher efficiency in free radical photopolymerization. Finally, a direct laser writing approach was successfully used to fabricate 3D objects.