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In this work, three new photoinitiators, based on the phenothiazine scaffold as a chromophore and potentially bearing the oxime ester functionality as an initiating group are designed and synthesized for the free radical polymerization of acrylates, the cationic polymerization of epoxides, and the formation of interpenetrated polymer networks upon irradiation with a light emitting diode emitting at 405 nm. These phenothiazine‐based oxime and oxime esters revealed impressive photoinitiation ability manifested by excellent polymerization rates and high final reactive function conversions. Significantly, they can be used as both; one‐component (Type I) and two‐component photoinitiating systems. Photoinitiation mechanisms through which reactive species are produced are investigated by means of different complementary techniques including real‐time Fourier transform infrared spectroscopy, UV–visible absorption spectroscopy, electron spin resonance spectroscopy, fluorescence (steady state and time resolved), cyclic voltammetry, and molecular modeling calculations. Thermal initiation behavior of the different oxime esters is also studied by using differential scanning calorimetry, highlighting their dual thermal/photochemical initiation ability. Finally, 3D printed objects are successfully fabricated by conducting both direct laser writing and 3D printing experiments. [ABSTRACT FROM AUTHOR]

Different combinations of donors and acceptors of charge transfer complexes (CTCs) can realize visible light catalysis in multiple wavelength bands. Here, we successfully demonstrated that 2‐bromoacetophenone as an electron acceptor, combined with amines (for formation of CTC), can achieve photopolymerization under LED@405 nm visible light irradiation, initiating the polymerization of (meth)acrylates, and the induction time can be completely eliminated by condition optimization. The CTC was also shown to have dual photo/thermal initiation capability and was eventually applied to 3D printing as well. [ABSTRACT FROM AUTHOR]

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, a series of 5,12‐dialkyl‐5,12‐dihydroindolo[3,2‐a]carbazole‐based oxime‐esters with visible light absorption abilities is designed and synthesized. Notably, when irradiated with light‐emitting diodes at 405 nm, the proposed structures can undergo a direct cleavage of the NO 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 can be used as dual photo and thermal initiators. An interesting structure/reactivity/efficiency relationship can be obtained by comparing the reactivity of the different radicals generated upon photoexcitation at identical chromophore but also by comparing the photoinitiating ability of the hexyl derivatives (1)–(10) with that of methyl derivatives (1′)–(10′) characterized by a lower solubility than the previous series in resins. Chemical mechanisms are studied through different techniques including real‐time Fourier transform infrared spectroscopy, UVvisible absorption spectroscopy, fluorescence (time‐resolved or steady‐state) as well as molecular modeling calculations. To finish, OXEs are incorporated in new photosensitive 3D printing resins, furnishing 3D objects with a remarkable spatial resolution. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Many academic and industrial works are carried out for the search of new classes of visible light photoinitiators. In the last decade, new Type I photoinitiator generating silyl, germyl, or stannyl radicals is elegantly reported; the chemical mechanisms being often associated with the cleavage of the C(═O)Si, C(═O)Ge, or C(═O)Sn bonds. In this context, silyl glyoxylates are also reported as dual Type I and Type II photoinitiators. Silyl glyoximides are proposed here as new near‐UV and blue light sensitive photoinitiators. The synthesis of such compounds as well as their light absorption properties is discussed. Their photochemical properties are studied through steady state photolysis experiments and molecular modeling data (i.e., through the calculations of the frontier orbitals, CC bond dissociation energies and triplet state energy levels). To finish, their photoinitiating ability upon near‐UV or blue light emitting diode light is examined in a benchmark methacrylate monomer blend (BisGMA/TEGDMA). Markedly, a Type I photoinitiator behavior is highlighted but better initiating properties are found in multicomponent systems in combination with iodonium salt and amine. [ABSTRACT FROM AUTHOR]

Two water soluble oligomeric photoinitiators (OAA‐B and OAA‐BP) were synthesized by first preparing an oligo(amido amine) (OAA) via aza‐Michael addition reaction of N,N'‐methylene bisacrylamide and 1,4‐diaminobutane, then carrying out another aza‐Michael addition reaction between OAA and 4‐benzoylphenyl acrylate for OAA‐B and also diethyl vinylphosphonate for OAA‐BP. Photopolymerization kinetics of 2‐hydroxyethyl methacrylate (HEMA) and HEMA: poly(ethylene glycol) diacrylate (PEGDA, Mn = 575) mixture initiated by these photoinitiators were monitored by real‐time FTIR spectrophotometer and photo‐DSC. These photoinitiators together with bis‐(4‐tert‐butylphenyl)‐iodonium hexafluorophosphate (Iod) have high polymerization efficiencies under UV and unexpectedly visible light exposure. The efficiency of the photoinitiators is based on two separate mechanisms, oxidative interaction between benzophenone group and Iod and charge transfer complex (CTC) formation between Iod and amines in OAA; verified by absorption, steady state photolysis, electron spin resonance and laser flash photolysis. The CTC formation mechanism was also studied by molecular modeling studies; and both mechanisms generating aryl radicals. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

2‐Oxo‐2‐(tert‐butyldimethylsilyl)acetic acid (DKSi‐COOH), is proposed here as a new high‐performance photoinitiator (PI) for the free radical polymerization of methacrylates under blue light irradiation. In the presence of DKSi‐COOH, very good polymerization performances are reached and outstanding bleaching properties are obtained compared to traditionally used camphorquinone‐based photoinitiating systems. Remarkably, this new developed PI exhibits good water solubility and excellent stability in acidic conditions and represents therefore a promising candidate for water‐based formulations. [ABSTRACT FROM AUTHOR]

In this article, new compounds based on the carbazole scaffold (DMs = DM1 and DM2, constituted by a carbazole unit connected on positions 3 and 6 to a two 4,4′‐dimethoxydiphenylamine groups and differing by the substituent present on the nitrogen heteroatom of the carbazole core) were synthesized and proposed as high‐performance visible light photoinitiators/photosensitizers for both the free‐radical polymerization of methacrylates and the cationic polymerization of epoxides upon visible light exposure using LED@405 nm. Remarkably, DM2 leads to higher final conversions than DM1. In order to study the photophysical and photochemical properties of the carbazole derivatives, different parameters were taken into account such as the light absorption, the steady‐state photolysis, and the fluorescence spectroscopy. Using different techniques such as fluorescence quenching, redox behavior, and cyclic voltammetry, we are able to discuss the photosensitization/photoinitiation reactions providing a full coherent picture of the involved chemical mechanisms. The photosensitization of the carbazole derivatives occurred predominantly via singlet excited states at the rate of the diffusion limit. Upon exposure to laser diode at 405 nm, DMs show high performance in initiating systems for 3D resins. Remarkably, DM2 can also be used in photocomposite synthesis using light‐emitting diode conveyor. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 2081–2092 [ABSTRACT FROM AUTHOR]

Highlights • The first thioxanthone-functionalized monomeric photoinitiator with 1,6-heptadiene structure (TXdMA). • TXdMA absorbs at 435–439 nm, allowing better coverage of the emission spectra of the visible light sources compared to TX. • The photoinitiating efficiency of TXdMA was found to be similar to that of TX. • TXdMA has a very good migration stability compared to TX. Abstract 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 nm; with absorption redshift≈50 nm and ε 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. [ABSTRACT FROM AUTHOR]

Six new carbazole based compounds (Ca1–Ca6) are synthesized and proposed as high performance photoinitiators with iodonium salt (iod) and/or an amine (EDB) for both the free radical polymerization (FRP) of acrylates and the cationic polymerization (CP) of epoxides upon near UV and visible light exposure using light emitting diodes (LEDs) @385 nm and @405 nm. Excellent polymerization initiating abilities are found and high final reactive function conversions are acquired. A full picture of the involved photochemical mechanisms is given. [ABSTRACT FROM AUTHOR]

In the present paper, new photoinitiators based on the meta-terphenyl scaffold in combination with an iodonium salt and 9H-carbazole-9-ethanol (CARET) are proposed for the free radical promoted cationic polymerization of epoxides upon visible light exposure using light emitting diodes at 405, 455, and 470 nm. Remarkably, a new high performance additive (i.e., CARET) is proposed here for cationic polymerizations. CARET shows some important advantages compared to other reported additives such as N-vinylcarbazole or benzyl alcohol used as references. Excellent polymerization initiating abilities are found and a full picture of the involved chemical mechanisms is provided. [ABSTRACT FROM AUTHOR]

For polymer synthesis upon visible light, actual photoinitiator operates in a restricted part of the spectrum. As a consequence, several photoinitiators are necessary to harvest all of the emitted visible photons. Herein, 2,7-di- tert-butyldimethyldihydropyrene is used for the first time as a multicolor photoinitiator for the cationic polymerization of epoxides. Upon addition of diphenyliodonium hexafluorophosphate and optionally N-vinylcarbazole, the originality of this approach is to allow efficient monomer conversions under various excitation light sources in the 360-650 nm wavelength range: halogen lamps, and light-emitting and laser diodes. The synthesis of an interpenetrated polymer network from an epoxide/acrylate blend using a red light at 635 nm is also feasible. The formed polymer material exhibits a photochromic character. [ABSTRACT FROM AUTHOR]

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 [ABSTRACT FROM AUTHOR]

In this paper, nine organic compounds based on the coumarin scaffold and different substituents were synthesized and used as high-performance photoinitiators for free radical photopolymerization (FRP) of meth(acrylate) functions under visible light irradiation using LED at 405 nm. In fact, these compounds showed a very high initiation capacity and very good polymerization profiles (both high rate of polymerization (Rp) and final conversion (FC)) using two and three-component photoinitiating systems based on coum/iodonium salt (0.1%/1% w/w) and coum/iodonium salt/amine (0.1%/1%/1% w/w/w), respectively. To demonstrate the efficiency of the initiation of photopolymerization, several techniques were used to study the photophysical and photochemical properties of coumarins, such as: UV-visible absorption spectroscopy, steady-state photolysis, real-time FTIR, and cyclic voltammetry. On the other hand, these compounds were also tested in direct laser write experiments (3D printing). The synthesis of photocomposites based on glass fiber or carbon fiber using an LED conveyor at 385 nm (0.7 W/cm2) was also examined. [ABSTRACT FROM AUTHOR]

Photopolymerization processes, and especially those carried out under visible light, are more and more widespread for their multiple advantages compared to thermal processes. In the present paper, new 1,8-naphthalimide derivatives are proposed as photoinitiators for free-radical polymerization upon visible light exposure using light-emitting diodes (LEDs) at 395, 405, and 470 nm. These photoinitiators are used in combination with both iodonium salts and phosphine. The synthesis of these compounds as well as their excellent polymerization initiation ability for methacrylate monomers are presented in this article. A full picture of the involved chemical mechanisms is also provided thanks to photolysis, radical characterization, and redox measurements. [ABSTRACT FROM AUTHOR]

Two new near-UV and visible-light-sensitive photobase generators (PBGs) are synthesized and investigated. They are built on a near-UV and visible light sensitive ( E )-3-(2,2′-bithiophen-5-yl)-2-cyanoacrylic acid chromophore and a latent strong base such as 1,8-diazabicyclo [5.4.0] undec-7-ene (DBU) and 1,5,7-triazabicyclo [4.4.0] dec-5-ene (TBD). Upon irradiation, decarboxylation occurs and the base is released. The anionic curing of epoxy/thiol as well as thiol/divinylsulfone formulations in the presence of these PBGs under LEDs at 385 and 405 nm is studied. More than 60% of conversion of the thiol and epoxy functions is achieved upon LED@385 nm without any post baking. [ABSTRACT FROM AUTHOR]

Although there have been many reports on photoinitiating systems adapted to visible lights for radical photopolymerization, the challenge for the design and development of photoinitiating systems for cationic photopolymerization or concomitant radical/cationic photopolymerization (for interpenetrating polymer network IPN synthesis) with visible lights still remains open. Particularly, the recent development of cheap and easily accessible LEDs operating upon soft visible light irradiations has opened new fields for polymer synthesis. Since 2011, many novel photoinitiating systems based on organic and organometallic compounds with excellent visible light absorption have emerged and exhibited outstanding photoinitiating abilities especially for cationic photopolymerization. In this review, recent progress (mainly from 2011 to early 2014) in applications of photoinitiators and sensitive photoinitiating systems under visible lights are reported. In addition, their relative efficiencies in the photopolymerization of different monomers are exemplified and discussed. [ABSTRACT FROM AUTHOR]

Abstract: Nine new photoinitiating systems based on a combination of new and established dyes (having an end capped polyenic structure) with an iodonium salt have been synthesized and tested for the polymerization of divinylether and epoxy monomers upon a visible light exposure. They exhibit a strong absorption in the 350–650 nm range which well matches the visible light emission of different convenient visible light sources. Interestingly, very soft irradiation conditions can be employed. Excellent polymerization profiles have been obtained from selected dye iodonium salt combinations using a halogen amp or a laser diode à 457 nm. The chemical mechanisms associated with these novel photoinitiating systems are investigated by steady-state photolysis and ESR experiments. [Copyright &y& Elsevier]

Abstract: Several diketopyrrolopyrrole derivative based dyes (DPP), combined with an iodonium salt or an amine (and optionally an additive), are studied as photoinitiating systems for the cationic polymerization CP of epoxides or the free radical polymerization FRP of acrylates under different irradiation sources i.e. a very soft halogen lamp as well as laser diodes at 473 nm (blue light) and 532 nm (green light). The diketopyrrolopyrrole-furan derivative (FuDPP) is very efficient in CP. The structure/reactivity/efficiency relationships in this series of DPP derivatives are investigated. A comparison with a well known reference for visible light photoinitiating system (i.e. camphorquinone based photoinitiating system) is also provided showing the better efficiency of the new proposed structures. The photochemical mechanisms are studied by steady state photolysis, fluorescence, cyclic voltammetry, laser flash photolysis and electron spin resonance spin-trapping techniques. [Copyright &y& Elsevier]

Thiophene and polythiophene derivativeshave been prepared andused as photoinitiators upon visible light exposure. Their abilitiesto initiate, when combined with an iodonium salt (and optionally N-vinylcarbazole), a ring-opening cationic photopolymerizationof epoxides and radical photopolymerization of acrylates under variousdifferent irradiation sources (i.e., very soft halogen lamp irradiation,laser diode at 405, 457, 473, 532, and 635 nm and blue LED bulb at462 nm) have been investigated. These systems are characterized bya remarkable performance for purple to red light exposure. They arealso particularly efficient for the cationic and radical photopolymerizationof an epoxide/acrylate blend in a one-step hybrid cure and lead tothe formation of an interpenetrated polymer network IPN (30 s forgetting tack-free coatings). Their migration stability is excellentin the cured IPNs. The photochemical mechanisms are studied by steadystate photolysis, fluorescence, cyclic voltammetry, electron spinresonance spin trapping, and laser flash photolysis techniques. [ABSTRACT FROM AUTHOR]