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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 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.

Four series of bis-chalcone compounds based on benzylpiperidinone, tetrahydrothiopyranone, pyridine or biphenyl central parts are designed and synthesized, enabling the development of ten bis-chalcones varying both by the central cores and by the substitution patterns (ortho, meta, para-positions) and the choice of the different groups attached to the peripheral substituents (alkoxy or allyloxy-substituted aromatic rings, thiophene, or ferrocene). In this series of ten bis-chalcones, eight of them were never synthesized before (i.e. only bis-chalcones 8 and 10 were already reported albeit never used as photoinitiators). These different dyes are proposed as new near-UV/visible light sensitive photoinitiators, in combination with an amine and an iodonium salt, to initiate the free radical photopolymerization (FRP) of PEG-diacrylate and the cationic photopolymerization (CP) of EPOX under LED@405 nm and LED@375 nm irradiation conditions. For the photopolymerization of acrylates carried out between thin films in laminate, all the bis-chalcones proposed in this work show higher photoinitiation abilities upon irradiation with a LED at 375 nm than at 405 nm, which is mainly due to their excellent light absorption properties in the near-UV region. Markedly, in contrast with the other two series of bis-chalcone compounds, pyridine-based bis-chalcones prove to be the most efficient photoinitiators, especially the bis-chalcones 5 and 9. Furthermore, all of them can also promote the cationic polymerization of epoxides upon LED irradiation at 375 nm, in the presence of an iodonium salt and an amine. More interestingly, some 3D patterns fabricated through the free radical polymerization of PEG-diacrylate demonstrate reversible swelling properties and shape-memory for access to 4D printing.

In this paper, seven new photoinitiators based on the benzophenone scaffold are specifically designed for photopolymerization under mild conditions upon light-emitting diode (LED) irradiation, i.e. four benzophenone-triphenylamine photoinitiators (denoted as BT1-BT4) and three benzophenone-carbazole photoinitiators (denoted as BC1-BC3). Noticeably, these structures have never been reported in the literature except for BT4, so these molecules have been specifically designed for photopolymerization applications. Remarkably, various combinations of chemical groups were investigated in this work to determine the effects of the substitution patterns on their photoinitiation abilities. The formation of benzophenone-triphenylamine and benzophenone-carbazole hybrid structures not only contributes to red-shift of the absorption maxima but also strongly enhances their molar extinction coefficients. The different compounds showed high photoinitiation abilities upon irradiation with an LED@405 nm, and the free radical photopolymerization of acrylates and the cationic polymerization of epoxides could be promoted with high final function conversions (e.g. 77% for the BT3/iodonium salt/amine system in free radical photopolymerization). Remarkably, these new PIs are also able to sensitize sulfonium salts upon irradiation @405 nm. Markedly, because of the benzophenone moiety, a monocomponent Type II PI behavior could be observed, e.g. these compounds could initiate the polymerization alone. Remarkably, benzophenone-triphenylamine compounds BT2, BT3 and BT4 exhibited better hydrogen abstraction abilities as Type II photoinitiators than the benchmark and commercial photoinitiator 2-isopropylthioxanthone in the absence of amines as well as in the presence of amines. Furthermore, the interaction between the photoinitiators and the different additives was investigated by steady state photolysis and fluorescence quenching experiments. The free radical generation in the BT3/amine system wa

The investigation and clarification of the photoinitiation mechanism of novel systems are of importance for the design and development of compounds with high photoinitiation efficiency of photopolymerization. Some disubstituted aminoanthraquinone derivatives have been reported to exhibit interesting photochemical/photophysical properties and have the potential to act as high performance multicolor photoinitiators under the irradiation of various wavelengths of visible light from light-emitting diodes (LEDs). Herein, three disubstituted aminoanthraquinone derivatives, i.e., 1-amino-4-hydroxyanthraquinone, 1,4-diaminoanthraquinone, and 1,5-diaminoanthraquinone, with iodonium salt and N-vinylcarbazole as additives, have been investigated. Their photoinitiation mechanism was studied using fluorescence spectroscopy, laser flash photolysis, steady state photolysis, computational quantum chemistry, and electron spin resonance spin trapping techniques. Then, their photoinitiation ability for the cationic photopolymerization of epoxide and divinyl ether monomers under the irradiation of diverse LEDs (i.e., blue, green, yellow, and red LEDs) was investigated. The types and positions of substituents were found to play a vital role in the photoreactivity and photoinitiation ability of the disubstituted aminoanthraquinone derivative-based photoinitiating systems.

Multihydroxy-anthraquinone derivatives [i.e., 1,2,4-trihydroxyanthraquinone (124-THAQ), 1,2,7-trihydroxyanthraquinone (127-THAQ), and 1,2,5,8-tetrahydroxyanthraquinone (1258-THAQ)] can interact with various additives [e.g., iodonium salt, tertiary amine, N-vinylcarbazole, and 2-(4-methoxystyryl)-4,6-bis(trichloromethyl)-1,3,5-triazine] under household green LED irradiation to generate active species (cations and radicals). The relevant photochemical mechanism is investigated using quantum chemistry, fluorescence, cyclic voltammetry, laser flash photolysis, steady state photolysis, and electron spin resonance spin-trapping techniques. Furthermore, the multihydroxy-anthraquinone derivative-based photoinitiating systems are capable of initiating cationic photopolymerization of epoxides or divinyl ethers under green LED, and the relevant photoinitiation ability is consistent with the photochemical reactivity (i.e., 124-THAQ-based photoinitiating system exhibits highest reactivity and photoinitiation ability). More interestingly, multihydroxy-anthraquinone derivative-based photoinitiating systems can initiate free radical crosslinking or controlled (i.e., reversible addition−fragmentation chain transfer) photopolymerization of methacrylates under green LED. It reveals that multihydroxy-anthraquinone derivatives can be used as versatile photoinitiators for various types of photopolymerization reactions.

Four N-[2-(dimethylamino)ethyl]-1,8-naphthalimide derivatives (ANNs) with different substituents (bromo group, primary amine, secondary amine, and tertiary amine) in the naphthalimide skeleton have been synthesized and can be used as one-component free radical photoinitiators or incorporated into multi-component photoinitiating systems for free radical or cationic photopolymerization under the irradiation of various LEDs. ANN2 (with secondary amine substituent) or ANN3 (with tertiary amine substituent) alone is capable of initiating the free radical polymerization of acrylates under a LED at 405 nm while ANN0 (with bromo substituent) or ANN1 (with primary amine substituent) does not work. When combined with various additives (e.g. iodonium salt, N-vinylcarbazole, chloro triazine, or tertiary amine), most of the ANN1–3 based multi-component photoinitiating systems are efficient in free radical photopolymerization at 385 nm, 405 nm, 455 nm, 470 nm and even under a low-intensity polychromatic visible light (from a halogen lamp) with the final conversions being higher than 60% (even more efficient than commercial photoinitiators bisacylphosphine oxide and camphorquinone). In addition, ANN1–3 based photoinitiating systems also exhibit a high efficiency for cationic photopolymerization of epoxides upon diverse LEDs. The ANN2 based photoinitiating system can also be used for the synthesis of interpenetrated polymer networks and adapted for 3D printing. The photochemical mechanisms of the ANN based systems have been comprehensively investigated and discussed in detail.

The photochemical mechanism of the radical generation from photoinitiating systems based on 1, 8‐naphthalimide derivatives (ANDs; with tertiary amine moieties) are investigated by using various approaches including cyclic voltammetry, steady‐state photolysis, and electron spin resonance spin‐trapping techniques. It reveals that radicals can be produced from ANDs alone or ANDs/additive (e. g. iodonium salt or chloro triazine) combinations. The generated radicals and cations can initiate both free‐radical and cationic photopolymerization reactions under irradiation with various light‐emitting diodes or a halogen lamp. For most of the AND‐based photoinitiating systems, more than 60 % of acrylate or epoxide conversions were attained, and were even higher than those obtained by using commercial photoinitiators, for example, bisacylphosphine oxide or camphorquinone. More interestingly, the AND1‐based photoinitiating system can also initiate concomitant cationic/radical polymerizations and can be used for the synthesis of interpenetrated polymer networks.

N-Phenylglycine is normally used as a co-initiator and can be photodecomposed by different dyes under UV or visible light irradiation to generate radicals for the initiation of free radical photopolymerization. However, the photochemistry and photoinitiation ability of N-phenylglycine alone upon exposure to near-UV light (e.g., UV LED at 392 nm), to the best of our knowledge, have not been investigated. In this research, the photochemistry of N-phenylglycine under the UV LED at 392 nm is studied using various approaches, and it reveals that radicals (PhNHCH2•) can be produced from the direct photodecomposition of N-phenylglycine. In addition, N-phenylglycine can also interact with iodonium salt under the UV LED at 392 nm to generate phenyl radicals and cations. These formed active species exhibit high performance to initiate the free radical photopolymerization of acylates and cationic photopolymerization of epoxides and divinyl ethers.