Double Role of Diphenylpyridine Derivatives as Fluorescent Sensors for Monitoring Photopolymerization and the Determination of the Efficiencies of the Generation of Superacids by Cationic Photoinitiators

Novel fluorescent sensors with electron-donating or electron-withdrawing substituents incorporated into a chromophore group based on 2,6-diphenylpyridine were designed and synthesised. The spectroscopic properties of these compounds were studied. Moreover, the positive solvatochromism of 2,6-bis-(4-methylsulphanylphenyl)pyridine (PT-SCH3) in selected solvents was studied by measurement of the absorption and emission spectra and analysed using the Dimroth–Reichardt solvent parameter set. After that, the performance of a series of 2,6-diphenylpyridine derivatives as fluorescent molecular sensors for monitoring free-radical and cationic photopolymerization processes by the Fluorescence Probe Technique (FPT) was studied. As a consequence of this stage of research, the effect of substituents on the sensitivity of the 2,6-diphenylpyridine derivatives as sensors during photopolymerization has been evaluated and discussed. It has been found that compounds containing strong electron-donating substituent (PT-SCH3) slightly shift their fluorescence spectrum during the free-radical polymerization of monomer, which enables the monitoring of the polymerization progress using the fluorescence intensity ratio measured at two different wavelengths as the progress indicator. The position of the fluorescence spectrum of 2,6-diphenylpyridine derivatives with electron-withdrawing substituents is practically insensitive to changes occurring in their environment. Hence, it is recommended to use these compounds with different indicators of the progress of the photopolymerization process based on normalised intensity of fluorescence (Imax/I0). Among the compounds studied, 2,6-bis(4-methylsulphanylphenyl)pyridine (PT-SCH3) turned out to be the best fluorescent sensor for the purpose of monitoring free-radical polymerization by FPT. Consequently, the dual application of the selected 2,6-diphenylpyridine derivatives is proposed: (a) as fluorescent sensors for monitoring the free-radical photopolymerization progress, and (b) as spectroscopic sensors for the determination of efficiencies of the generation of superacids by cationic photoinitiators during the cationic photopolymerization process. Finally, a new method for determining the relative efficiency of the photogeneration of superacids during the photo cleavage of onium salt has been devised and applied for the evaluation of the performance of 2,6-diphenylpyridine derivatives

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

Luminescent Molecular Chemosensors for Rapid and Nondestructive Detection of Thickness of Polymer Coatings

Molecular chemical sensor, especially optical luminescent sensor, technologies are a rapidly growing topic in science and product design, embracing development in chemistry, biochemistry and life science research. [...

New, highly versatile bimolecular photoinitiating systems for free-radical, cationic and thiol–ene photopolymerization processes under low light intensity UV and visible LEDs for 3D printing application

1-Amino-4-methyl-naphthalene-2-carbonitrile derivatives are proposed for the role of photosensitizers of iodonium salt during the photopolymerization processes upon near UV-A and visible ranges. Remarkably, 1-amino-4-methyl-naphthalene-2-carbonitrile derivatives are highly versatile allowing access to photoinitiating systems for (i) the cationic photopolymerization of epoxide monomers with a ring opening mechanism and vinyl ether monomers with chain growth mechanisms (ii) the free-radical photopolymerization of acrylate monomers, (iii) the photopolymerization of interpenetrated polymer networks (IPNs) based on epoxide and acrylate monomers under air and under laminate in an oxygen-free atmosphere (iv) the thiol–ene photopolymerization processes. Excellent polymerization profiles are obtained during all types of photopolymerization processes. The initiation mechanisms are analyzed through steady state photolysis, cyclic voltammetry and fluorescence experiments. Moreover, the newly developed bimolecular photoinitiating systems were investigated by applying an additive manufacturing process under visible light sources. Furthermore, vat photopolymerization processes using IPN compositions, which are polymerizable by using new photoinitiating systems, provide high resolution and speeds. For these reasons, new bimolecular photoinitiating systems are promising initiators for photopolymerization-based 3D printing process to fabricate 3D structures