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

Abstract

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.

Visible-Light-Mediated Organophotocatalyzed C(sp3)–H Activation and Intramolecular Cyclization

“…In recent years, the use of pyrylium salts as organic photocatalysts in complex synthetic organic transformations has been expanding. 4 Because of their similar photoredox behavior and reactivity, pyrylium analogues can mimic widely used acridinium photocatalysts. 5 Moreover, these pyrylium salt catalysts are easily prepared in a single step from commercially available cheap derivatives of benzaldehyde or acetophenone.…”

Recent Advances on Quinoxaline-Based Photoinitiators of Polymerization

“…In addition, photopolymerization constitutes an appealing polymerization technique, which exhibits numerous specificities and advantages compared to traditional thermal polymerization. In order to illustrate this, the possibility of polymerizing without solvents to obtain efficient spatial and temporal control during the polymerization process can be cited as relevant examples [16][17][18][19][20][21][22][23][24][25][26][27][28][29]. Development of photo-initiating systems is not new since the first report mentioning a photoinduced electron transfer between triethanolamine and electron-accepting dyes (xanthenes, acridines, thiazines) was reported as soon as 1954 by Oster and coworkers [30].…”

Novel multi-material photo-curable resins containing high-performance photoinitiating systems and nano additives dedicated to 3D-VAT printing

“…For the role of co-initiators, tertiary amines are usually employed. Ketone derivatives are used as photoinitiators of the second type, among which benzophenone, 43,44 thioxanthone 45–48 or camphoroquinone 49,50 are distinguished.…”