Photochemical study of a new bimolecular photoinitiating system for vat photopolymerization 3D printing techniques under visible light

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

Applicability of 1,6-Diphenylquinolin-2-one Derivatives as Fluorescent Sensors for Monitoring the Progress of Photopolymerisation Processes and as Photosensitisers for Bimolecular Photoinitiating Systems

The applicability of new 1,6-diphenylquinolin-2-oneas derivatives as fluorescent molecular sensors for monitoring the progress of photopolymerisation processes by Fluorescence Probe Technique (FPT) has been tested. The progress of cationic, free-radical and thiol-ene photopolymerisation for commercially available monomers: triethylene glycol divinyl ether (TEGDVE), trimethylolpropane triacrylate (TMPTA) and trimethylpropane tris(3-mercaptopropropionate) (MERCAPTO) was monitored. It was found that new derivatives of 1,6-diphenylquinolin-2-one shifted their fluorescence spectra towards shorter wavelengths with the progress of polymerisation, which enabled monitoring the progress in terms of fluorescence intensity ratios as the progress indicator. Derivatives of 1,6-diphenylquinolin-2-one show sensitivity to changes in both polarity and viscosity in the surrounding microenvironment during photopolymerisation processes. Therefore, it was shown that they are good candidates to act as fluorescent sensors for monitoring the kinetics of very quick processes, such as photopolymerisation processes. Furthermore, the effect of the nature of substituents attached to the 1,6-diphenylquinolin-2-one ring on the characteristics of emission spectra was identified. Moreover, the sensitivity of fluorescent sensors was compared with commercially available model sensors, such as 7-diethylamino-4-methylcoumarin (Coumarin 1) and trans-2-(2′,5′-dimethoxyphenyl)ethenyl-2,3,4,5,6-pentafluorobenzene (25ST). Moreover, it was also proven that selected derivatives of 1,6-diphenylquinolin-2-one exhibit an accelerating effect on the progress of cationic photopolymerisation of vinyl monomers (TEGDVE). Thus, the new 1,6-diphenylquinolin-2-one derivatives can be successfully used both as molecular fluorescence sensors to monitor the progress of photopolymerisation processes and as diaryliodonium salt photosensitisers to initiate cationic photopolymerisation processes in a UV-A range of 365 nm