In this work, we presented a new bimolecular photoinitiating system based on 2-amino-4,6-diphenylpyridine-3-carbonitrile derivatives as visible photosensitizers of diphenyliodonium salt. Real-time FTIR and photo-DSC photopolymerization experiments with a cycloaliphatic epoxide and vinyl monomers showed surprisingly good reactivity of the bimolecular photoinitiating systems under UV-A, as well as under visible light sources. Steady-state photolysis, fluorescence experiments, theoretical calculations of molecular orbitals, and electrochemical analysis demonstrated photo-redox behavior as well as the ability to form initiating species via photo-reduction or photo-oxidation pathways, respectively. Therefore, the 2-amino-4,6-diphenylpyridine-3-carbonitrile derivatives were also investigated as a type II free-radical photoinitiator with amine. It was confirmed that the 2-amino-4,6-diphenylpyridine-3-carbonitrile derivatives, in combination with different types of additives, e.g., amine as a co-initiator or the presence of onium salt, can act as bimolecular photoinitiating systems for cationic, free-radical, and thiol-ene photopolymerization processes by hydrogen abstraction and/or electron transfer reactions stimulated by either near-UV or visible light irradiation. Finally, the 2-amino-4,6-diphenylpyridine-3-carbonitrile derivatives were selected for 3D printing rapid prototyping experiments. Test objects were successfully printed using purely cationic photosensitive resin, created on a 3D printer with a visible LED light source.

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.

The performance of a series of 2-amino-4,6-diphenyl-pyridine-3-carbonitrile derivatives as fluorescent molecular sensors for monitoring photopolymerization processes of different monomers by the Fluorescence Probe Technique (FPT) was studied. It has been shown that the new derivatives are characterized by much higher sensitivity than the commercially available 7-diethylamino-4-methylcoumarin (Coumarin 1) and trans-2-(2′,5′-dimethoxyphenyl)ethenyl-2,3,4, 5,6-pentafluorobenzene (25ST) probes. It has been discovered that the 2-amino-4,6-diphenyl-pyridine-3-carbonitrile derivatives accelerate the cationic photopolymerization process initiated with diphenyliodonium photoinitiators at the wavelength where the photoinitiator alone does not work. They are particularly efficient for the photoinitiation of cationic photopolymerization of an epoxide and vinyl monomers. Consequently, the application of the 2-amino-4,6-diphenyl-pyridine-3-carbonitrile derivatives in a dual role: (a) as fluorescent sensors for monitoring the free-radical, thiol-ene and cationic polymerization progress, and (b) as long-wavelength co-initiators for diphenyliodonium salts initiators, is proposed.

The Langmuir monolayer technique has been successfully used for decades to model biological membranes and processes occurring at their interfaces. Classically, this method involves surface pressure measurements to study interactions within membrane components as well as between external bioactive molecules (e.g. drugs) and the membrane. In recent years, surface-sensitive techniques were developed to investigate monolayers in situ ; however, the obtained results are in many cases insufficient for a full characterization of biomolecule-membrane interactions. As result, description of systems using parameters such as mixing or excess thermodynamic functions is still relevant, valuable and irreplaceable in biophysical research. This review article summarizes the theory of thermodynamics of single- and multi-component Langmuir monolayers. In addition, recent applications of this approach to characterize surface behaviour and interactions (e.g. orientation of bipolar molecules, drug-membrane affinity, lateral membrane heterogeneity) are presented.