Visible-Light Amine Thioxanthone Derivatives as Photoredox Catalysts for Photopolymerization Processes

Herein, mono- and disubstituted thioxanthones have been synthesized and introduced as photosensitizers of iodonium salt for cationic and free-radical photopolymerization of epoxy and an acrylate monomer, respectively. Photoinitiation activity of these molecules was verified during photopolymerization processes performed upon exposure to visible LEDs of 420, 455, and 470 nm. The kinetics of the photopolymerization processes was followed using FT-IR spectroscopy. Moreover, the developed compounds were proposed as strongly reducing metal-free photoredox catalysts in organocatalyzed atom transfer radical polymerization (ATRP). Thioxanthone derivatives (with alkyl halide) efficiently activate the ATRP of methyl methacrylate using a visible LED as an irradiation source. The formed polymers in the ATRP process were characterized by SEC. Apart from studying the photopolymerization processes with the participation of obtained thioxanthones, absorption, fluorescence, as well as electrochemical properties of thioxanthone derivatives were investigated. Furthermore, the performance of studied compounds in 3D printing applications was also examined. The most important result of this study is the design and possible application of photosensitizers/photocatalysts for photopolymerization processes.