3‑Hydroxyflavone and <i>N</i>‑Phenylglycine in High Performance Photoinitiating Systems for 3D Printing and Photocomposites Synthesis

We propose to use 3-hydroxyflavone as a versatile high performance visible light photoinitiator (PI) in combination with an amino acid (<i>N</i>-phenyl­glycine) for the free radical polymerization (FRP) of methacrylates in thick samples (e.g., 3D printing) or composites upon visible light exposure (light-emitting diode LED@405 nm or LED@477 nm). The high originality of this approach is the use of safer compounds in photoinitiating systems (combination flavone derivative/amino acid). 3-Hydroxyflavone can also be used in three-component systems with an iodonium salt and an amine for the cationic polymerization of epoxides upon exposure to near-UV light LED@385 nm. Also interestingly, a charge transfer complex (CTC) between <i>N</i>-phenylglycine NPG and iodonium salt gives also remarkable initiating performance for free radical polymerization of methacrylates upon mild light irradiation conditions (LED@405 nm). High polymerization initiating abilities are found, and high final reactive function conversions are obtained. The use of the new proposed initiating systems as materials for laser write or 3D printing experiments was also especially carried out with the formation of printed green fluorescent photopolymers. This green fluorescence obtained with naturally occurring 3-hydroxyflavone compound can be ascribed to the excited state intramolecular proton transfer ESIPT character. A full picture of the included photochemical mechanisms is given. Remarkably, the 3-hydroxyflavone/amino acid system is also very efficient for photocomposites synthesis with glass fibers (thick samples with good depth of cure) using UV or LED@395 nm conveyor

π‑Conjugated Dithienophosphole Derivatives as High Performance Photoinitiators for 3D Printing Resins

Photopolymerization and 3D printing applications upon near-UV or visible light are currently limited to both rather low polymerization speed and thin layer by layer productions (below 100 μm) using photoinitiating systems (PIS) mainly inherited from the 1990s. Filling the need for new PIS, two π-conjugated dithienophosphole derivatives (DTPs) are synthesized and proposed as high performance near-UV and visible light photoinitiators/photoredox catalysts for both free radical polymerization (FRP) of (meth)­acrylates and cationic polymerization (CP) of epoxides (e.g., using light-emitting diode (LED) at 405 nm). Astounding polymerization initiating abilities are found, and high final reactive function conversions are obtained (for multifunctional monomers). Their utilization as materials in laser write and 3D printing experiments is especially carried out with for the first time, about 2 mm 3D printed photopolymers in a one-layer approach. A full picture of the included photochemical mechanisms is additionally given. Originally, dithienophosphole derivatives are featured as metal-free photoinitiators/photoredox catalysts