Photoinitiator-catalyst systems based on meta-terphenyl derivatives as photosensitisers of iodonium and thianthrenium salts for visible photopolymerization in 3D printing processes

Abstract

This work demonstrates a new versatile, efficient photoinitiating system based on 2-amino-4-phenyl-6-(4-phenylphenyl)benzene-1,3-dicarbonitrile and 2-amino-4-phenyl-6-[4-[(E)-styryl]phenyl]benzene-1,3-dicarbonitrile derivatives as photosensitisers of iodonium and thianthrenium salts for photopolymerization under visible low light intensity with potential translation to high performance 3D printing. The new meta-terphenyl derivatives were characterised by standard analytical and spectroscopic techniques. The activity of new bimolecular photoinitiating systems was investigated using Fourier transform real-time infrared spectroscopy. As the choices for an efficient visible sensitiser are rather limited for thianthrenium salt, the syntheses of new photo-sensitisers have received considerable attention. Therefore, the main goal of this study was to apply meta-terphenyl derivatives as visible photosensitisers for different types of onium salts. For this purpose, the new 2-amino-4-phenyl-6-(4-phenylphenyl)benzene-1,3-dicarbonitrile and 2-amino-4-phenyl-6-[4-[(E)-styryl]phenyl]benzene-1,3-dicarbonitrile derivatives were combined with commercially available iodonium salt (HIP) and thianthrenium salt to create visible light photoinitiating systems. It was shown that the efficiency of these bimolecular photoinitiating systems was based on the favorable free energy change of the photoinduced electron transfer from the meta-terphenyl derivatives to the iodonium and thianthrenium salts. It was confirmed by the experiments that the ability of tested photoredox pairs to initiate the photopolymerization processes depends on the oxidation potentials of the meta-terphenyl derivatives and the reduction potentials of the onium salts. Here, we explore the role of the scientific aspects of the mechanism, energetics and dynamics of applicability of the new meta-terphenyl compounds as efficient and versatile photosensitisers of onium salts with different oxidising power. Moreover, the investigated terphenyl derivatives can work as photoredox catalysts and efficient photoinitiating systems, and can be used with typical oxidation and reduction agents in both reductive and oxidation cycles.