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International audience; From a circular plastic economy perspective, a new configuration of Metal Acetylacetonate Bidentate Ligand Interaction (MABLI) mechanism adapted to the chemistry of the recyclable Elium® thermoplastic resins has been recently discovered to initiate the free radical polymerization of these resins under mild conditions (under air, at room temperature, non-purified monomers, absence of hazardous chemical substances). This initiating strategy is based on the synergy between the initial MABLI couple and a phosphine oxide (Type I photoinitiator). Despite the absence of irradiation, the mere presence of the phosphine oxide reduced significantly the curing time and the final conversion obtained is nearly 100%. In order to dismantle the role of each component and to predict new highperformance MABLI redox initiating systems based on a similar configuration, a mechanistic study was pursued. It has resulted in the identification of new hybrid complexes obtained by ligand exchange between the photoinitiator and the metallic complex. On the other hand, presence of the Type I photoinitiator can level up the initiating strategy by combining MABLI and photoactivation into a dual cure approach: thereby, the photolysis yield and the polymerization efficiency of the complexed form of the phosphine oxide was studied and compared to the free form of the photoinitiator.

The development of light-mediated controlled radical polymerization has benefited from the discovery of novel photocatalysts, which could allow a precise light control over the polymerization process and the production of well-defined polymers. Here, we introduce oxygen-doped anthanthrene (ODA) as effective organic photocatalysts for photoinduced energy/electron transfer reversible addition-fragmentation chain-transfer (PET-RAFT) polymerization. ODA phtocatalysts featur strong visible light absorption (e455 nm up to 2.4 x 104 M–1cm–1), ease-of-synthesis, a certain oxygen-tolerance, and high stability, which enables the photo-regulated RAFT polymerization with extremely low catalyst loading (0.1-10 ppm) and excellent control under visible light or sunlight. Furthermore, this organocatalytic living radical process is adaptable to the polymerization of a range of monomers including methyl methacrylate, butyl acrylate, styrene, and N,N-dimethyl acrylamide, and also the synthesis of diblock and decablock copolymers under metal-free conditions.

International audience; In this work, a series of Type I photoinitiators (PIs) based on the naphthoquinone scaffold were designed and synthesized for the first time, in order to induce photopolymerization under visible light. As a result, these PIs exhibit excellent photoinitiation abilities in the presence of acrylates monomers upon LED@405 or @455 nm irradiation. Interestingly, some compounds have better photoinitiation performance than the benchmark Type I phosphine-oxide i.e. diphenyl(2,4,6trimethylbenzoyl)phosphine oxide (TPO) upon exposure to LED@455 nm. Chemical mechanisms supporting the photopolymerization process were investigated through different techniques as well as theoretical calculations. In addition, the new proposed structures were also investigated in two-component photoinitiating systems and exhibited a higher efficiency in free radical photopolymerization. Finally, direct laser write approach is successfully used to fabricate 3D objects.

In order to discuss the polymerization effect from the substituted position and methoxy group of Type I photinitiators, a series of naphthalene-based oxime esters was designed and synthesized. Compared to the 2-naphthalene-substituted compound, the UV absorption region of the 1-naphthalene-based compound was greatly improved. In addition, the methoxy substitution exhibited longer absorption characteristics than did the methoxy-free one. The photochemical reaction behavior of these novel compounds was also studied by photolysis, cyclic voltammetry (CV), and electron spin resonance (ESR) experiments. Finally, the initiation abilities of naphthalene-based oxime esters toward trimethylolpropane triacrylate (TMPTA) monomer were conducted through the photo-DSC instrument under UV and a 405@nm LED lamp. Remarkedly, the naphthalene-based oxime ester (NA-3) that contains 1-naphthalene with o-methoxy substituent showed the rather red-shifted absorption region with the highest final conversion efficiency under UV (46%) and 405@nm LED (41%) lamp irradiation.

In this work, free radical photopolymerization (FRP) kinetics for series of different phenylamine oxime ester structures (DMA-P, DEA-P, DMA-M, TP-2P, TP-2M and TP-3M) was investigated. Steric hindrance and branched substituents were prepared to realize the corresponding electronic and photopolymerization effects. The photophysical, electrochemical, thermal properties and radical concentration were investigated by UV-visible spectroscopy, cyclic voltammetry (CV), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and electron paramagnetic resonance (EPR). Furthermore, the structure-reactivity relationships were also studied in detail through photo-DSC experiment. We demonstrate that the introduction of alkyl chains and/or numbers of oxime esters affects significantly the photoreactivity. Under the same weight ratio of formulation and irradiated condition, TP-3M containing three oxime esters in its structure and methyl group in the periphery exhibits the highest double-bond conversion efficiency. TP-3M-based formulation also shows a wide operation window under different contents and light intensities. Importantly, the photoreactivity of the TP-3M-based system was found to be better than the commercial photoinitiator (OXE-01) under LED@405 nm at a low concentration. This work could provide some significance to the design of oxime esters with enhanced photoreactivity.

International audience; In this work, eleven heteroleptic copper complexes were designed and studied as photoinitiators of polymerization in three-component photoinitiating systems in combination with an iodonium salt and an amine. Notably, ten of them exhibited panchromatic behavior and could be used for long wavelengths. Ferrocene-free copper complexes were capable of efficiently initiating both the radical and cationic polymerizations and exhibited similar performances to that of the benchmark G1 system. Formation of acrylate/epoxy IPNs was also successfully performed even upon irradiation at 455 nm or at 530 nm. Interestingly, all copper complexes containing the 1,1′-bis(diphenylphosphino)ferrocene ligand were not photoluminescent, evidencing that ferrocene could efficiently quench the photoluminescence properties of copper complexes. Besides, these ferrocene-based complexes were capable of efficiently initiating free radical polymerization processes. The ferrocene moiety introduced in the different copper complexes affected neither their panchromatic behaviors nor their abilities to initiate free radical polymerizations.

International audience; In this work, six new fluorescent dyes derived from the naphthalimide scaffold (Napht1–Napht6) were synthesized and used as high-performance photoinitiating systems (PISs) in two and three-component systems (combined with iodonium salt (Iod) and/or an electron donor amine (such as N-phenylglycine[NPG])) for the radical photopolymerization of acrylate and methacrylate monomers under visible light using a light-emitting diode at 405 nm. Markedly, these dyes were never synthesized before. In fact, these PISs showed high initiation efficiency with both demonstrating high final reactive function conversions and high polymerization rates. A further interest of our study is to determine the effect of the different substituents (chromophoric group) on the naphthalimide function, concerning the efficiency of initiation of the free radical polymerization. In order to improve the mechanical properties of the obtained polymers, these derivatives were also tested for the photopolymerization of a blend of acrylate/epoxy monomers (TA/EPOX); these latter properties were characterized by traction tests. To demonstrate the initiation efficiency of these dyes, several methods and characterization techniques were used, including steady state photolysis, real-time Fourier transform infrared spectroscopy, emission spectroscopy as well as cyclic voltammetry. In our study, these naphthalimides were used for the synthesis of photocomposites (one and multiple layers of glass fibres) using a UV@395 nm (4 W/cm2) conveyor, as well as in the preparation of 3D printed polymers. Markedly, one of the naphthalimide derivatives (Napht-4) can be used as a new high-performance water soluble photoinitiator for photopolymerization in water and hydrogel synthesis.

Four visible light triphenylamine-based oxime ester photoinitiators (TP-1–4) were synthesized and confirmed successfully through 1H NMR, 13C NMR, and electron impact mass spectrometry (EI-MS) measurements as well as elementary analyses (EA). The design strategy for triphenylamine substituted photoinitiators involved the use of hydrogen atoms only for TP-1, one methoxy group for TP-2, two methoxy groups for TP-3 and two methyl groups for TP-4. The incorporation of triphenylamine derivatives in oxime esters gives near UV and visible light absorption characters with maximum absorption peaks at around 360 nm. Upon using a UV lamp as an irradiation source, all the oxime esters showed good double bond conversion efficiency in a range of 72–92% in the free radical polymerization of trimethylolpropane triacrylate (TMPTA) through photo-DSC experiments. Among all, TP-1 displayed the highest final conversion efficiency. Accordingly, the photochemical reaction behavior was studied using photolysis, cyclic voltammograms (CV), electron spin resonance (ESR) and theoretical calculations. Additionally, selected photoinitiating systems exhibited outstanding 3D patterns with high resolution and good edge definition through direct laser write (DLW) experiments @405 nm. This work thus demonstrates a judicious chemical design to fine-tune the photopolymerization character in triphenylamine oxime ester analogues.

Herein, new iodonium salts based on a 4,4-difluoro-1,3,5,7,8-pentamethyl-4-bora-3a,4a-diaza-s-indecene (B-1) chromophore have been introduced to 3D printing applications. Iodonium salts with different anions such as tosylate, hexafluorophosphate, hexafluoroantimonate, and triflate absorbing in the range up to 600 nm are reported. The usefulness of the new BODIPY derivatives in initiating cationic photopolymerization processes such as epoxide, vinyl ether, oxetane, and glycidyl monomers in the wavelength range from 365 to 520 nm was confirmed using real-time FT-IR and photo-DSC methods. The initiation efficiency of a one-component system was also compared with that of a two-component system consisting of the chromophore (the same as that used for conducting iodonium salts) and iodonium salt – bis-(4-t-butylphenyl)-iodonium hexafluorophosphate. Moreover, the photochemical mechanisms were investigated by steady-state photolysis, ESR fluorescence experiments, theoretical calculations of molecular orbitals, and electrochemical analysis. These studies allowed us to determine the effect of the anion type in iodonium salts on the rate of proton acid generation. The BODIPY derivatives are also efficient for the initiation of cationic and free-radical polymerization. Optical microscopy experiments demonstrated that different patterns can be obtained by experiments with resolution test targets and 3d-printing. Moreover, photoinitiators based on the B-1 chromophore can be used not only for initiating the photopolymerization processes but also as colorimetric sensors for measurements of the degree of photopolymerization.

By virtue of remarkable spatial resolution, a metal-free visible LED photopolymerization process, initiated by imidazole based charge transfer complexes under mild conditions (room temperature, without an inert atmosphere, monomer purification or stabilizer removal), is reported. For two multifunctional acrylate monomers, an outstanding photoinitiating ability was proved (up to 80% of acrylate function conversion) by combining imidazoles (electron donors) and iodonium salts (electron acceptors) under 405 nm LED irradiation. 3D printing experiments using a low intensity 3D printer are reported to demonstrate the performance of this CTC approach. Meanwhile, the thermal polymerization features a relatively low thermal initiating temperature, making the process more pursuable and also easier to achieve for thick samples in practice and/or polymerization in shadow areas (where light does not penetrate). As a new dual photo/thermal initiator, it showcases tremendous potential for 3D printing with high resolution and high-tech composites. This dual initiating system represents a new type of thermal initiator toward a safer way (peroxide-free) and provides a new pathway for surface repairing or modifying of direct laser writing in a low toxicity, facile manner.

A new organic photocatalyst (9,10-bis[(triisopropylsilyl)ethynyl]anthracene, An-Si) is proposed here for the formation of free radicals under very soft irradiation conditions under air through a photoredox catalysis. It works according to an oxidative cycle that uses the combination of An-Si, a diphenyl iodonium salt along with a silane. This behavior is highlighted through an investigation of its excited state and redox properties. The different chemical intermediates are characterized by ESR experiments. In addition, the reversibility of the oxidation reaction of An-Si was investigated by cyclic voltammetry. This three-component system is able to promote the ring-opening photopolymerization of an epoxide as well as the free radical photopolymerization of an acrylate upon household LED bulb and Xe lamp exposure. Excellent polymerization profiles (mainly in ROP) are obtained. The specific properties of this catalyst are outlined.

International audience; This work is devoted to the study of two copper complexes (Cu) bearing pyridine ligands, which were synthesized, evaluated and tested as new visible light photoinitiators for the free radical photopolymerization (FRP) of acrylates functional groups in thick and thin samples upon light-emitting diodes (LED) at 405 and 455 nm irradiation. These latter wavelengths are considered to be safe to produce polymer materials. The photoinitiation abilities of these organometallic compounds were evaluated in combination with an iodonium (Iod) salt and/or amine (e.g., N-phenylglycine—NPG). Interestingly, high final conversions and high polymerization rates were obtained for both compounds using two and three-component photoinitiating systems (Cu1 (or Cu2)/Iodonium salt (Iod) (0.1%/1% w/w) and Cu1 (or Cu2)/Iod/amine (0.1%/1%/1% w/w/w)). The new proposed copper complexes were also used for direct laser write experiments involving a laser diode at 405 nm, and for the photocomposite synthesis with glass fibers using a UV-conveyor at 395 nm. To explain the obtained polymerization results, different methods and characterization techniques were used: steady-state photolysis, real-time Fourier transform infrared spectroscopy (RT-FTIR), emission spectroscopy and cyclic voltammetry.

In both organic and polymer synthesis, photochemistry of charge transfer complexes (CTCs) is considered as a powerful approach to expand visible-light-driven radical chemistry reaction. One reports herein on the development of a class of useful CTCs using pyridinium salts as efficient electron acceptors (combined with N, N, 3,5-tetramethylaniline, TMA) to achieve a multiwavelength (375-560 nm) metal-free LED photopolymerization process under mild conditions (open to air, without monomer purification and inhibitor removal). The UV-vis absorption spectra and molecular modeling simultaneously verify its potential blue-green absorbing wavelength range. Also, their good thermal initiation behavior at relatively low temperatures makes it easier to achieve thick samples and/or polymerization in the shadow region in practice. More importantly, with excellent photoinitiating capability, the formulation is successfully applied to direct laser write (DLW) and high-resolution 3D printing, yielding a series of objects with well-defined structures, such as letters, ring, solid squares, and chess pieces. These new pyridinium salt acceptors further extend the applicability to visible photopolymerizable resins and additive-containing formulations for efficient surface and deep curing.

International audience; In order to expand the application of oxime-esters (OXEs) and to introduce a one-component photoinitiating system of high performance in visible light photopolymerization, we designed and synthetized a series of 5,12-dihexyl-5,12-dihydroindolo[3,2-a]carbazole-based oximeesters with visible absorption abilities. Notably, when irradiated with light-emitting diodes at 405 nm, the proposed structures could undergo a direct cleavage of the NO bond followed by decarboxylation, generating free radicals capable to efficiently initiate free radical photopolymerizations (FRP). Furthermore, the new OXEs showed good thermal initiation abilities and could be used as dual photo and thermal initiators. An interesting structure/reactivity/efficiency relationship could be obtained by comparing the reactivity of the different radicals generated upon photoexcitation at identical chromophore but also by comparing the photoinitiating ability of our series of dyes with that of another series of dyes designed to exhibit a lower solubility in resins. Indeed, solubility of dyes can constitute a major issue adversely affecting the photoinitiating ability. Chemical mechanisms were studied through different techniques including real-time Fourier Transform Infrared Spectroscopy (RT-FTIR), UV-visible absorption spectroscopy, fluorescence (time-resolved or steady state) as well as molecular modelling calculations. Eventually, the usage of the investigated OXEs in new photosensitive 3D printing resins is also presented.

International audience; In this work, the design of an original series of coumarin derivatives (CoumC1-CoumC13) is presented. Chemical structures of these coumarins were selected by molecular modelling to ensure both excellent light absorption properties and high potential photoreactivity (high excited state energy). As a striking result of this in-silico design, 8 of the 13 proposed coumarins were never presented and were specifically proposed for this work, evidencing the interest of the structures. New multi-component photoinitiating systems (PISs) based on these coumarins are proposed for the free radical polymerization (FRP) of (meth)acrylates and examined upon visible light irradiation using the light emitting diode (LED) as a safe and economical irradiation source. The proposed systems are based on coumarins which act as remarkable photoinitiators/photosensitizers (PIs/PSs) combined with N-phenylglycine (NPG) and/or iodonium salt (Iod) as co-initiators in order to generate the reactive species (radicals) that will initiate the photopolymerization recation. Investigation of the chemical mechanisms suggested by the different interactions that take place as well as the photophysical and photochemical properties of coumarins are provided. The access 2 to high polymerization rates (Rp), excellent photoinitiating abilities and great reactive function conversions (FC) is possible with these structures based on the coumarin core. Coumarins show high efficiency for the FRP of (meth)acrylates by reaction with iodonium salt (a photo-oxidation process) or with amine (a photo-reduction process). These compounds were used in 3D printing resins but also for the preparation of photocomposites. In this latter case, an excellent depth of cure was noted as remarkable behavior. To rationalize the experimental results, a kinetic model for a three-component system has been established to analyze the role of oxygen in the monomer conversions and the conversion enhancement observed while using an amine as a co-initiator.

International audience; In this research, 31 nitrocoumarins (including 27 structures never reported in the literature) were designed through molecular orbital calculations and synthesized as high-performance near-UV−visible light photoinitiators of polymerization for a better understanding of their sructure/ eactivity/ efficiency relationship. Based on their photoinitiating abilities examined during the free-radical polymerization (FRP) of acrylates, different coumarins examined in this work can be classified into three main categories: (1) very reactive ones (Coum6,7,11,12&26); (2) moderately reactive nitrocoumarins (Coum1,2,16,20,21,23,25,27&28); and (3) nitrocoumarins of low reactivity (Coum3,4,5,8,9,10,13,14,15,17,18,19,22,24,29,30&31). Different techniques were used in order to understand their photoinitiating abilities as well as the associated chemical mechanisms. The real-time Fourier transform infrared technique has been used to follow the polymerization profiles (reactive function conversion (FCs) vs irradiation time). Different two- and three-component photoinitiating systems based on nitrocoumarin/iodonium salt (or N-phenylglycine (NPG) or ethyl 4-(dimethylamino)benzoate) and nitrocoumarin/iodonium salt/NPG were examined for the FRP of acrylates or/and the cationic polymerization of epoxides upon irradiation with a light-emitting diode at 405 nm as an unharmed and inexpensive irradiation source. Moreover, cyclic voltammetry, fluorescence spectroscopy, UV−visible spectroscopy, and electron spin resonance techniques were also used to provide a full picture of the involved chemical mechanisms. Excellent polymerization performances (i.e., high final reactive FCs and also great rates of polymerization (Rp)) were obtained using these derivatives. Some applications in threedimensional printing and composite synthesis are reported to highlight the interest of the proposed structures in modern technologies.

International audience; In this work, we propose the use of flavones that can be derived from natural products as versatile high performance visible light photoinitiators initially with amino acid and later with iodonium salt and phosphino benzoic acid combinations for free‐radical polymerization acrylates of thin specimen (25 μm) and methacrylates thick specimen (1.4 mm) upon illumination with near ultraviolet light or visible light utilizing light emitting diodes (LED)@385 nm and LED@405 nm. High polymerization initiating capabilities are found with different hydroxyflavones and high final conversions of the reactive function are obtained. Their application as materials for three‐dimensional (3D) printing patterns is especially carried out for 1 mm thick 3D printed photopolymers. A full description of the comprised photochemical mechanisms is additionally given.

International audience; The photoinitiation abilities of three 1,2-diketones [i.e., acenaphthenequinone (ANPQ), aceanthrenequinone (AATQ), and 9,10-phenanthrenequinone (PANQ)]-based photoinitiating systems [PISs, with additives such as iodonium salt, N-vinylcarbazole (NVK), tertiary amine, and phenacyl bromide (R-Br)] for cationic photopolymerization and free-radical photopolymerization under the irradiation of ultraviolet (UV; 392 nm) or blue (455 nm) light-emitting diode (LED) bulb are investigated. All 1,2-diketones studied exhibit ground state absorption that match with the emission spectra of UV (392 nm) or blue LED (455 nm) better than that of the well-known blue-light-sensitive photoinitiator camphorquinone (CQ). In particular, AATQ/iodonium salt/NVK can show high photoinitiating ability (with epoxide conversion yield >70%) under the UV light irradiation due to the effect of NVK. In addition, 1,2-diketone/iodonium salt (and optional NVK) systems are capable of initiating free-radical photopolymerization of methacrylates, with conversions of 50–58%. Furthermore, some 1,2-diketone/tertiary amine (and optional R-Br) combinations are found to demonstrate high efficiency to initiate free-radical photopolymerization, and 71% of methacrylate conversion can be achieved with PANQ/tertiary amine/R-Br PIS. Some 1,2-ketone-based PISs can even exhibit higher efficiency than the CQ-based systems. The photochemical mechanism of the radical generation from the 1,2-diketone-based PISs is investigated and found to be consistent with the related photopolymerization efficiency.

This paper describes the development of four new coumarin chromophore-based iodonium salts as efficient one-component cationic photoinitiators upon light-emitting diode (LED) irradiation with maximum emission under the UV-A region at 365 nm and under visible light at 405 nm. They initiate the cationic polymerization of epoxides, oxiranes, and glycidyl and vinyl ethers upon exposure to a UV-A LED and a visible LED. Even small structural variations of iodonium cations carrying different types of aryl moieties and the same coumarin chromophore can affect their properties. The properties and reactivities of a series of iodonium salts containing various cations were compared in the context of different photopolymerization processes. The relationship between the molecular structure of the coumarin-based iodonium salts and their reaction mechanism during the different photopolymerization processes was also investigated. Based on the results from real-time FT-IR spectroscopy and photo-differential scanning calorimetric experiments, it was concluded that the structures of the cations strongly affect the photopolymerization reaction rate and the final conversion of the monomer. Photopolymerization kinetic data show that kinetic parameters are affected by the presence of substituents in the phenyl ring of coumarin scaffold based iodonium salts. Indeed, the photoinitiating process remains highly efficient during the ring opening cationic photopolymerization of epoxides, oxiranes and glycidyl monomers, as well as during the extremely fast photopolymerization of vinyl monomers. The photochemical mechanisms of these new salts are investigated for the first time through electron spin resonance, laser flash photolysis and steady-state photolysis experiments and the cyclic voltammetry technique. Molecular orbital calculations are also used to shed some light on the initiation mechanisms. In conclusion, we have shown that new cationic iodonium photoinitiators are interesting from an industrial point of view because they can be used as efficient initiators in constructing IPN polymeric materials in the 3D printing area. These insights can encourage the utilisation of new coumarin based iodonium salts as useful photoinitiators in polymer coating synthesis, as well as for 3D printing processes.

New 2-(diethylamino)-4,6-diphenyl-benzene-1,3-dicarbonitrile derivatives were synthesized and proposed as high-performance photoinitiators in conjunction with iodonium salts for: (i) the cationic polymerization of epoxides, (ii) the free-radical polymerization of acrylates, and (iii) the synthesis of interpenetrating polymer networks (IPNs) from acrylate/epoxy blends. Investigated photoinitiating systems exhibit initiating efficiency upon exposure to soft irradiation conditions of visible light-emitting diodes (LEDs) with emission maxima at 405 nm and 420 nm. Excellent polymerization profiles are obtained during photopolymerization processes. The studied photoinitiating systems were also used for photosensitive resins for laser writing/3D printing experiments upon exposure to a laser diode at 405 nm. The photophysical and photochemical properties, i.e., absorption, steady-state photolysis and fluorescence spectroscopy, of terphenyl derivatives were studied. A photoinitiation mechanism related to the production of cations and radicals was studied using fluorescence quenching experiments, laser flash photolysis, cyclic voltammetry and electron spin resonance.

In this article, four new phenothiazine derivatives (denoted as PT1, PT2, PT3 and PT4) are specifically in silico designed by molecular modelling for good light absorption properties @405 nm. The most interesting structures showing both intense violet/blue light absorption and high potential photochemical reactivity were synthesized for detailed investigations as photoinitiators/photosensitizers in the presence of an iodonium salt for the free radical photopolymerization of (meth)acrylates and the cationic polymerization of epoxides upon near-UV or visible light irradiation. Remarkably, two of the proposed structures (PT3 and PT4) from this in silico design were never synthesized prior to this work and were thus specifically designed for this work. Three-component photoinitiating systems based on PT/iodonium/amine (N-phenylglycine or ethyl 4-dimethylaminobenzoate) are also developed for the free radical polymerization of acrylates. Both excellent polymerization rates and high final reactive function conversions were obtained. A full picture of the photochemical mechanisms is provided using different techniques: real-time Fourier transform infrared spectroscopy, UV-visible spectroscopy, fluorescence spectroscopy, and cyclic voltammetry. Finally, the high performance of the phenothiazine derivatives is also shown in 3D printing experiments as well as in photocomposite synthesis using glass fibres (thick sample; using a LED@395 nm conveyor).

International audience; Three thioxanthone derivatives differing by their peripheral groups have been investigated as visible light photoinitiators of polymerisation. Their reactivity and efficiency have been compared with that of a commercial type II photoinitiator (2-isopropylthioxanthone-ITX) in the case of free radical polymerisation, cationic polymerisation and interpenetrated polymer networks synthesis for 25 m or 1.4 mm thick samples under a 405 nm LED irradiation. They are incorporated into either, a two-component system with an iodonium salt or an amine, or a three-component system combining an iodonium salt and an amine. Using absorption and fluorescence spectroscopies, laser flash photolysis and molecular modelling, optical properties, excited state energies and lifetimes of these thioxanthone derivatives have been determined allowing a better understanding of the associated chemical mechanisms. Interestingly, the main reaction pathway for one of these thioxanthone derivatives in the photoinitiating systems was determined as involving its singlet state S1 whereas ITX and thioxanthones are known to react from their triplet excited state T1. The high efficiency of the new initiating systems was found as being worthwhile for laser write applications @405 nm but also for high migration stability.

International audience; The free radical polymerization of acrylates photo-initiated by push–pull dye-based photoinitiating systems (PISs) is widely investigated in previous works. As a supplementary investigation on push–pull dyes, here in this article, 25 push–pull structures comprising electron acceptors derived from indane-1,3-dione and 1H-cyclopenta[b]naphthalene-1,3(2H)-dione (series 1) and 4-dimethoxyphenyl-1-allylidene moieties (series 2) and various electron donors are synthesized and examined as innovative structures for photoinitiation. Among the two series of dyes examined in this work and by monitoring the polymerization processes by RT-FTIR measurements, four dyes are determined as exhibiting excellent photoinitiation performances and these dyes are selected to perform further studies concerning the chemical mechanisms occurring inside the three-component PISs, for example, steady state photolysis, fluorescence quenching measurements, and cyclic voltammetry. Markedly, their reactivity is also proved by photoinitiation performance upon sunlight. These results prompt us to develop high performance push–pull dyes as photosensitizers and sunlight can be used as a mild and ecofriendly light source, which can advantageously replace LEDs for the free radical photopolymerization in the future. Finally, the formation of 3D patterns with an excellent gradient of resolution is successfully achieved by the direct laser write (DLW) with/without silica fillers.

International audience; A series of 50 oxime esters bearing various substituents were designed and synthesized as photoinitiators (48 of them were never synthesized before and only B1 and B10 were reported). Good light absorption properties in the visible range were observed for these oxime esters. Some structures exhibited better photoinitiation abilities than diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO) upon exposure to a LED@405 nm. Interestingly, PIs with methyl substituent on the oxime ester group have better photoinitiation performance than the others. Substituent effects were investigated through molecular orbitals calculations, the detection of CO2, and the investigation of the generated free radicals. The results demonstrate that the substituents on the oxime ester group exert major effects on the photoinitiation ability via the decarboxylation reaction. In addition, a chemical mechanism was proposed. 3D printed objects were successfully obtained by using the most reactive oxime ester as photoinitiator, and their thermal initiation behaviors of several oxime esters were also studied (dual thermal/photochemical initiator behavior).

International audience; In this paper, a series of coumarin chromophore-based oxime-esters was designed and synthesized as visible light photoinitiators (PIs). Interestingly, upon exposure to irradiation of a LED at 405 nm, the investigated oxime-esters (OXEs) could undergo a direct photocleavage, followed by decarboxylation, generating active free radicals capable to effectively initiate acrylate polymerization. Seven of the 10 investigated OXEs have never been synthesized in the literature. Markedly, the new proposed structures exhibit also thermal initiation ability and can be used as dual photo and thermal initiators. In addition, the oxime-ester system was also paired with an iodonium salt and exhibited a higher efficiency in free radical polymerization (FRP). The chemical mechanisms and the structure/reactivity/efficiency relationships were investigated through different techniques including real-time Fourier Transform Infrared Spectroscopy (RT-FTIR), UV-visible absorption spectroscopy, fluorescence (time-resolved or steady state), cyclic voltammetry as well as molecular modelling calculations. As a proof of their remarkable polymerization performance, the new OXEs were also used at 405 nm for direct laser write applications.

In this article, five new organic dyes based on the naphthalimide scaffold (Napht-1–Napht-5) were synthesized and tested as high-performance photoinitiators for both the Free Radical Photopolymerization (FRP) of acrylates and the Cationic Polymerization (CP) of epoxides using blue Light-Emitting Diodes (LEDs) as a safe irradiation source (LED @405 nm and 455). In fact, very good photopolymerization profiles (high final conversions and high polymerization rates) were obtained once these photoinitiators were combined with an Iodonium salt (Iod) or Iod/amine NPG and NVK). Remarkably, these dyes were able to generate interpenetrating polymer networks (IPN) by polymerization of a blend of monomers. These experiments were carried out to improve the polymerization profiles as well as the mechanical properties of the obtained materials. Due to their high photoinitiation abilities, these compounds were used in some applications such as photocomposite synthesis, direct laser write, and 3D printing experiments. To determine the chemical mechanisms, the photochemical/photophysical properties of these compounds were studied using different characterization techniques such as UV–visible absorption spectroscopy, steady-state photolysis, Fluorescence quenching, time-resolved fluorescence spectroscopy, FTIR spectroscopy, and cyclic voltammetry

International audience; In this article, ten organic dyes based on keto-coumarin (KC) derivatives (MeO-Coum1, MeO-Coum10) have been synthesized and characterized as high performance photoinitiators for the Free Radical Photopolymerization (FRP) of acrylates upon visible light exposure using a LED @405nm. The addition of Iodonium salt (Iod), amine [ethyl dimethylaminobenzoate (EDB) or N-phenylglycine (NPG)] and Iod/NPG couple in the photocurable resins have been carried out in order to prove their influences on the improvement on the photoinitiating abilities of keto-coumarins. The different dyes showed a very high ability to initiate the FRP by introduction of these additives, using Two or Three-component photoinitiating systems based on MeO-Coum/Iod or amine (0.1% or 0.4%/1% w/w) or MeO-Coum/Iod/NPG (0.1% or 0.4%/1%/1% w/w/w) respectively. In fact, these photoinitiators have been tested in different applications. For example: in direct laser write to generate 3D patterns using a laser diode @405nm, or for the photocomposite synthesis based on glass fibers. To characterize the initiation ability and to explain the reaction mechanisms in the photoinitiation step, several techniques have been used, such as UV-visible absorption spectroscopy and steady state photolysis, fluorescence emission, RT-FTIR, cyclic voltammetry and Electron Spin Resonance (ESR) spectroscopy.

Some efficient acylphosphine oxides have been used for many years as photoinitiators of radical polymerization. As very few new acylphosphine oxide compounds have been proposed these past years for...

Ascorbic acid is widely used in the food industry as a source of vitamin C or as antioxidant. However, it degrades quickly in beverages at acidic pH and can accelerate the degradation of anthocyanins, natural dyes used in beverages, leading to a loss of color. In this work, we investigated the possibility to replace ascorbic acid by ascorbic acid derivatives to prevent its degradation effect on anthocyanins from natural extracts (black carrot, grape juice, and purple sweet potato). For this, the thermal and photolytic stabilities under air and under N2 of ascorbic acid (as reference) and of some ascorbic acid derivatives (3-O-ethyl-l-ascorbic acid, 2-O-α-d-glucopyranosyl-l-ascorbic acid, l-ascorbic acid 2-phosphate sesquimagnesium salt hydrate, l-ascorbyl 2,6-dibutyrate, glyceryl ascorbate, (+)-5,6-O-isopropylidene-l-ascorbic acid), soluble in aqueous model beverages, were studied alone and in the presence of anthocyanins from the natural extracts in citrate buffer at pH 3. The stability was followed by UV-visible spectrometry. To extend the investigation, some properties of the ascorbic acid derivatives (pKa, oxidation potential, bond dissociation energy, ionization potential) were also determined. Moreover, the addition of chlorogenic acid was examined to further stabilize the mixture of anthocyanins with 2-O-α-d-glucopyranosyl-l-ascorbic acid, a promising ascorbic acid derivative.

Anthocyanins are natural dyes widely used in the food industry, but their chemical stability in beverages can be affected by the presence of additives. In the present paper, the interaction between anthocyanins and ascorbic acid (AA) is more particularly investigated. Ascorbic acid is an ubiquitous component in food products. In this study, the thermal stability at 43 °C and the photolysis stability in air and in an inert atmosphere (N2) of anthocyanins extracted from black carrot (BC), grape juice (GJ), and purple sweet potato (SP) were studied in the presence and absence of ascorbic acid (in citrate buffer at pH 3). Discriminating the main environmental factors (i.e., heat and light) affecting anthocyanin stability is a key point for better understanding the degradation pathways. The stability of the anthocyanins was followed by UV-vis spectrometry. Moreover, to understand the degradation mechanisms in both the presence and absence of ascorbic acid, various techniques such as fluorescence quenching, cyclic voltammetry, and electron-spin-resonance (ESR) spectroscopy were also used to furnish a full coherent picture of the chemical mechanisms associated with the anthocyanin degradation. In addition, molecular orbitals and bond-dissociation energies (BDE) were calculated to extend the investigation. Moreover, the effects of some supplementary stabilizers (chlorogenic acid, sinapic acid, tannic acid, fumaric acid, β-carotene, isoquercitrin, myricitrin, green coffee bean extract, and rosemary extract) and sugars (sucrose, fructose, and glucose) on anthocyanins stability in the presence of ascorbic acid were examined.

Diamino-anthraquinone derivatives [1,4-bis(isopropylamino)anthraquinone (SB36), 1-amino-4-anilinoanthraquinone (SB68), and 1,4-bis(p-tolylamino)anthraquinone (SG3)] exhibit absorption maxima in red light wavelength range and demonstrate broad ground state light absorption from ultraviolet to infrared light. When combined with coinitiators (e.g. iodonium salt), SB36-based photoinitiating systems exhibit the highest photoinitiation efficiency among all the studied diamino-anthraquinone derivative-based combinations for both cationic and free radical photopolymerization upon exposure to a red LED bulb. And SB36-based systems even demonstrate higher photoinitiating ability for free radical photopolymerization than that of previously studied 1,4-bis(pentylamino)anthraquinone (i.e. oil blue N)-based systems. In contrast, SG3-based photoinitiating systems show the lowest photoinitiation efficiency especially for free radical photopolymerization. Interestingly, the SB36/iodonium salt/N-vinylcarbazole system is a capable multicolor photoinitiating system able to initiate both cationic and free radical photopolymerization under the irradiation of UV to red LED bulbs and IR lamp. The photochemical mechanism associated with the production of cations and radicals from the diamino-anthraquinone derivative-based photoinitiating systems are investigated using steady state photolysis, fluorescence, laser flash photolysis, and electron spin resonance spin-trapping techniques.

The synthesis of the first photoinitiator (PI) based on thioxanthone (TX) with 1,6-heptadiene structure is described. This PI (TXdMA) absorbs in the near UV-vis region (435-439 rim; with absorption redshift approximate to 50 nm and e values comparable to TX). Photopolymerization results demonstrate that although TXdMA is not an effective one-component polymerizable photoinitiator, it can successfully initiate photopolymerization of poly(ethylene glycol) diacrylate (PEGDA, M-n = 250 D) and trimethylolpropane triacrylate (TMPTA) in the presence of bis-(4-tert-butylphenyl)-iodonium hexafluorophosphate (Iod) similar to TX/Iod. TXdMA exhibits better migration stability than TX. Absorption, fluorescence, steady state photolysis and cyclic voltammetry experiments are carried out to investigate the photochemical mechanisms.

Charge Transfer Complexes (CTCs) have recently been featured as new dual photo/thermal initiators, with attractive initiating features, such as in situ formation, high stability, spatiotemporal control, highly efficient process at room temperature (for the photochemical mode), reduced emissions of volatile organic compounds (VOCs) and high robustness in additive manufacturing and composite manufacturing. Extending the concept, in the present work, a series of CTCs formed between indoles (donors) and iodonium salt (acceptor) are investigated as safer and more stable dual thermal and photochemical free radical polymerization (FRP) initiators for benchmarked methacrylates. The formation of the CTCs is evaluated theoretically by Molecular Orbital (MO) calculations and experimentally using UV-vis spectroscopy. Remarkably, due to the in situ formation, safer storage ability as thermal initiators compared to traditional thermal initiators is demonstrated. As an additive manufacturing proof of concept, laser write experiments @405 nm show excellent spatial resolution performances. Dual approaches (photo/thermal curing) were also used to efficiently initiate both polymerization processes for the curing of glass fiber or carbon fiber composites, e.g. fast curing by light of the surface associated with a dark thermal curing in depth.

WOS:000451818000007; This paper is devoted to study two acridone derivatives (A-2DPA and A-2PTz). These acridone compounds are synthesized and proposed as high performance visible light photoinitiators, in the presence of an iodonium salt or/and an amine (NPG or EDB), for both the free radical polymerization of (meth)acrylates and the cationic polymerization of epoxides upon irradiation with LED@405 nm. Excellent polymerization initiating abilities are found, and high final monomer conversions are obtained. A full picture of the involved photochemical mechanisms is provided. This paper is also concerned with the use of these acridone-based systems in new 3D printing resins. Finally, the usage of the new acridone derivatives for photopolyrners with low migration properties is particularly outlined.

International audience; In this article, a series of three-component photoinitiating systems (PISs) based on push-pull dyes are proposed. The systems are composed of the newly synthesized push-pull dyes and different co-initiators, namely an iodonium salt and a tertiary amine (ethyl dimethylaminobenzoate EDB). Photoinitiation abilities and photochemical properties of the different investigated photoinitiating systems were studied in detail. Notably, the mechanisms related to the polymerization efficiencies were determined using different techniques such as UV-visible absorption and fluorescence spectroscopy. Moreover, the photoinitiation abilities of the threecomponent systems for the sunlight-induced polymerization processes were also 2 examined, indicating that sunlight can act as an effective light source for photopolymerization. Finally, 3D patterns with a spatial resolution were successfully produced by the direct laser writing (DLW) approach, even with photosensitive resins containing silica fillers.