Naphthalimide-Based Dyes as Photoinitiators under Visible Light Irradiation and their Applications: Photocomposite Synthesis, 3D printing and Polymerization in Water

In this work, six new fluorescent dyes derived from the naphthalimide scaffold (Napht1–Napht6) were synthesized and used as high-performance photoinitiating systems (PISs) in two and three-component systems (combined with iodonium salt (Iod) and/or an electron donor amine (such as N-phenylglycine[NPG])) for the radical photopolymerization of acrylate and methacrylate monomers under visible light using a light-emitting diode at 405 nm. Markedly, these dyes were never synthesized before. In fact, these PISs showed high initiation efficiency with both demonstrating high final reactive function conversions and high polymerization rates. A further interest of our study is to determine the effect of the different substituents (chromophoric group) on the naphthalimide function, concerning the efficiency of initiation of the free radical polymerization. In order to improve the mechanical properties of the obtained polymers, these derivatives were also tested for the photopolymerization of a blend of acrylate/epoxy monomers (TA/EPOX); these latter properties were characterized by traction tests. To demonstrate the initiation efficiency of these dyes, several methods and characterization techniques were used, including steady state photolysis, real-time Fourier transform infrared spectroscopy, emission spectroscopy as well as cyclic voltammetry. In our study, these naphthalimides were used for the synthesis of photocomposites (one and multiple layers of glass fibres) using a UV@395 nm (4 W/cm2) conveyor, as well as in the preparation of 3D printed polymers. Markedly, one of the naphthalimide derivatives (Napht-4) can be used as a new high-performance water soluble photoinitiator for photopolymerization in water and hydrogel synthesis.