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The utilization of two‐component systems comprising camphorquinone (CQ) and aromatic amines has become prevalent in the photopolymerization. However, there are still concerns about the safety of this CQ/amine system, mainly because of the toxicity associated with the leaching of aromatic amines. In light of these concerns, this study aims to develop novel coinitiator combinations featuring CQ and amines which cannot be leached out of materials, enabling free radical polymerization of representative dentalmethacrylate resins under blue light irradiation. This approach involves the initial design and analysis of hydrogen donors with low C─H bond dissociation energy through molecular modeling. Subsequently, copolymerizable methacrylate functional groups are incorporated via chemical modification, allowing it to act as both coinitiator and copolymerization monomer to achieve low migrationand leachability properties. This work presents, for the first time, the synthesis of the innovative coinitiator and compares its performance with the benchmark CQ/ethyl‐4‐dimethylaminobenzoate (EDB)‐based photoinitiation system (PIS). The results demonstrate the effectiveness of the newly proposed PIS. Finally, an in‐depth investigation is conducted into the reaction mechanism associated with this PIS through molecular orbital calculations and electron spin resonance studies. [ABSTRACT FROM AUTHOR]

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 this work, new naphthoquinone‐based photoinitiators are synthesized and applied for the first time in free radical photopolymerization. In the presence of acrylate monomers, these PIs display excellent photoinitiation capabilities under blue‐light LED@405 nm irradiation in a two‐component photoinitiating system in which the additive is a common iodonium salt (bis‐(4‐tert‐butylphenyl)iodonium hexafluorophosphate ‐ Iod) or a tertiary amine (ethyl 4‐dimethylaminobenzoate ‐ EDB). In controlled tests, the polymerization performance of dye4/Iod is equal to or better than that of common commercial Type II photoinitiators (2‐isopropylthioxanthone and benzophenone). Meanwhile, only a trace amount of photoinitiator is required (as low as 0.05%) to initiate the photopolymerization. It is worth noting that some of these compounds can also be used in one‐component photoinitiating system (monocomponent Type II behavior) and exhibit high photoinitiation ability. A series of complementary characterization analyses of two new naphthoquinone dyes (i.e. dye 1 and dye 4) with very similar chemical structures are carried out to investigate the relevant photochemical mechanism. Finally, 3D printing experiments are carried out by a simple and convenient Direct Laser Write (DLW) technique. [ABSTRACT FROM AUTHOR]

Here, a benzaldehyde substituted diacetylene vesicle formed through a self‐assembly strategy in water is reported. Under UV irradiation, conjugated polydiacetylene (PDA) could be generated in the blue phase by 1,4‐addition topopolymerization. Furthermore, this newly developed PDA vesicle displays distinctive colorimetric response to triple stimuli, including temperature, pH, and organic amines. Specifically, a clear blue‐to‐purple‐to‐red chromatic transition is observed for the PDA vesicle upon a gradient heating procedure from 25 to 75 °C. Although no obvious colorimetric changes happen when the PDA vesicle is exposed to acidic environments, it gradually turns into red color in alkaline aqueous solution or atmosphere with increasing pH values. More interestingly, this PDA vesicle can serve as an excellent sensor to distinguish some typical aliphatic/aromatic amines based on its different colorimetric and morphologic transformation behaviors. It is suggested that the incorporated benzaldehyde head group in PDA plays an essential role for the resulting responsiveness to the various environmental stimuli. As the preparation method is simple and straightforward, the novel PDA vesicle introduced here holds great potential as a promising sensor with the naked eye. [ABSTRACT FROM AUTHOR]

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. [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]

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. [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]

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. [ABSTRACT FROM AUTHOR]

A series of Type I photoinitiators (PIs) based on a nitrocarbazole scaffold are developed and examined for the first time as photoinitiators for visible light photopolymerization. Three oxime esters (OXE‐M, OXE‐V, OXE‐P) varying by the terminal groups (acetyl, acryloyl and benzoyl) attached via the oxime ester group are originally prepared. As a result of this, the three PIs exhibit excellent photoinitiation abilities in the presence of acrylate monomers upon LED@ 405 nm irradiation. Markedly, OXE‐M exhibits a better performance than the benchmark Type I phosphine‐oxide (diphenyl(2,4,6‐trimethylbenzoyl)phosphine oxide TPO). Chemical mechanisms supporting the polymerization process with these PIs are investigated by steady state photolysis, molecular orbital calculations and real‐time Fourier transformed infrared spectroscopy. After the cleavage of N─O bond and decarboxylation, free radicals are generated to initiate the free radical polymerization efficiently. Free radical photopolymerization of OXE‐M is applied in direct laser write and 3D printing. Interestingly, OXE‐M exhibits thermal initiation behaviors in monomers and can be used as dual photo and thermal initiators. The highly opaque feature of carbon fibers makes it difficult for light penetration, so dual photo/thermal curing are used here to prepare carbon fiber composites. [ABSTRACT FROM AUTHOR]

In the development of 3D printing fuels, there is a need for new photoinitiating systems working under mild conditions and/or leading to polymers with new and/or enhanced properties. In this context, we introduce herein N‐heterocyclic carbene–borane complexes as reagents for a new type of photo‐click reaction, the borane–(meth)acrylate click reaction. Remarkably, the higher bond number of boranes relative to thiols induced an increase of the network density associated with faster polymerization kinetics. Solid‐state NMR evidenced the strong participation of the boron centers on the network properties, while DMA and AFM showed that the materials exhibit improved mechanical properties, as well as reduced solvent swelling. [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]

Free radical polymerization upon near‐infrared (NIR) light is still the subject of intense research efforts and remains a huge challenge particularly for long wavelengths (>1000 nm). In this study, a NIR sensitizer operating upon long wavelength (1064 nm) is proposed for an efficient polymerization of acrylate monomers. A new three‐component photoinitiating system is developed comprising the NIR sensitizer in combination with an Iodonium salt (Iod) and an amine. Remarkably, the NIR sensitizer (IR 1064) absorbing strongly in all the near infrared region (700–1200 nm) offers the possibility to use a broad range of irradiation wavelengths, i.e., examples are provided at 785 and 1064 nm. Such long wavelengths are characterized by many advantages such as a deeper penetration of light and therefore a better curing of the monomer but it is also much safer than UV light. Excellent performance is observed for the three‐component IR 1064/Iod/Amine system under air: high conversion of acrylate functions associated with a fast polymerization time. The use of IR 1064 as NIR sensitizer with a broad NIR absorption is—to the best of current knowledge—never proposed in the literature. The photoinitiating performances are studied using real‐time Fourier transform infrared spectroscopy. [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]

Abstract: 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. [ABSTRACT FROM AUTHOR]

Abstract: 1,3‐Dimethylimidazol‐2‐ylidene difluoroborane (NHC‐BF2H) was prepared in a one‐pot, two‐step reaction from the parent ligated borane (NHC‐BH3). The derived difluoroboryl radical (NHC‐BF2.) was generated by laser flash photolysis experiments and characterized by UV spectroscopy and rate‐constant measurements. It is transient and reacts quickly with O2. Unusually, it also reacts more rapidly with ethyl vinyl ether than with methyl acrylate. By this measure, it is the first electrophilic ligated boryl radical. Both NHC‐BH3 and NHC‐BF2H serve as co‐initiators in bulk photopolymerizations, converting both electron‐poor and electron‐rich monomers at roughly similar rates. However, the difluorinated coinitiator provides polymers with dramatically increased chain lengths from both monomers. [ABSTRACT FROM AUTHOR]

Abstract: 1,3‐Dimethylimidazol‐2‐ylidene difluoroborane (NHC‐BF2H) was prepared in a one‐pot, two‐step reaction from the parent ligated borane (NHC‐BH3). The derived difluoroboryl radical (NHC‐BF2.) was generated by laser flash photolysis experiments and characterized by UV spectroscopy and rate‐constant measurements. It is transient and reacts quickly with O2. Unusually, it also reacts more rapidly with ethyl vinyl ether than with methyl acrylate. By this measure, it is the first electrophilic ligated boryl radical. Both NHC‐BH3 and NHC‐BF2H serve as co‐initiators in bulk photopolymerizations, converting both electron‐poor and electron‐rich monomers at roughly similar rates. However, the difluorinated coinitiator provides polymers with dramatically increased chain lengths from both monomers. [ABSTRACT FROM AUTHOR]

Abstract: 1,3‐Dimethylimidazol‐2‐ylidene difluoroborane (NHC‐BF2H) was prepared in a one‐pot, two‐step reaction from the parent ligated borane (NHC‐BH3). The derived difluoroboryl radical (NHC‐BF2.) was generated by laser flash photolysis experiments and characterized by UV spectroscopy and rate‐constant measurements. It is transient and reacts quickly with O2. Unusually, it also reacts more rapidly with ethyl vinyl ether than with methyl acrylate. By this measure, it is the first electrophilic ligated boryl radical. Both NHC‐BH3 and NHC‐BF2H serve as co‐initiators in bulk photopolymerizations, converting both electron‐poor and electron‐rich monomers at roughly similar rates. However, the difluorinated coinitiator provides polymers with dramatically increased chain lengths from both monomers. [ABSTRACT FROM AUTHOR]

Abstract: 1,3‐Dimethylimidazol‐2‐ylidene difluoroborane (NHC‐BF2H) was prepared in a one‐pot, two‐step reaction from the parent ligated borane (NHC‐BH3). The derived difluoroboryl radical (NHC‐BF2.) was generated by laser flash photolysis experiments and characterized by UV spectroscopy and rate‐constant measurements. It is transient and reacts quickly with O2. Unusually, it also reacts more rapidly with ethyl vinyl ether than with methyl acrylate. By this measure, it is the first electrophilic ligated boryl radical. Both NHC‐BH3 and NHC‐BF2H serve as co‐initiators in bulk photopolymerizations, converting both electron‐poor and electron‐rich monomers at roughly similar rates. However, the difluorinated coinitiator provides polymers with dramatically increased chain lengths from both monomers. [ABSTRACT FROM AUTHOR]

Rubrene, a compound that exhibits green light absorption, interacts with an iodonium salt through its excited singlet state to generate cations and free radicals under a green laser line at 532 nm or a halogen lamp delivering a low light intensity of polychromatic visible light. The photochemical mechanisms are investigated by steady-state photolysis, fluorescence, electrochemistry, and electron spin resonance spin trapping techniques. The produced cations and free radicals initiate both the cationic photopolymerization of epoxides and the free radical photopolymerization of acrylates. Moreover, the addition of N-vinylcarbazole into the system enhances the photopolymerization efficiency. The Rubrene/amine/chlorotriazine photoinitiating system also exhibits a much higher photoinitiation ability for the free radical photopolymerization of acrylates. [ABSTRACT FROM AUTHOR]

A new photoinitiator based on a bis-silylketone (BSK) structure is proposed as a novel compound leading to highly efficient initiating silyl radicals for the polymerization of methacrylates (e.g., a bisphenol A-glycidyl methacrylate/triethyleneglycol dimethacrylate blend (70%/30% w/w)) upon exposure to a blue light emitting diode and a green laser diode. The polymerization profiles are recorded by real time Fourier transform IR (FTIR) spectroscopy. Absorption, fluorescence, electron spin resonance (ESR), and steady state experiments are used to investigate the involved chemical mechanisms. Molecular orbital calculations are also carried out. Remarkably, BSK efficiently works in the presence of an iodonium salt. The overall mechanism for the initiation step is clarified. This novel class of silyl radical generating photoinitiators is really promising for the photopolymerization of methacrylates, e.g., in dental materials. [ABSTRACT FROM AUTHOR]

In this article, novel azahelicenes (AZs) were synthesized and proposed as high performance visible light photoinitiators for both the free radical polymerization of acrylates and the cationic polymerization (CP) of epoxides upon visible light exposure using Light Emitting Diodes (LEDs) @405, @455, and @470 nm. Excellent polymerization initiating abilities are found and high final conversions were obtained. Remarkably, an exceptional long lifetime photoluminescence property of the polymer films was observed when synthesized in presence of AZs. A full picture of the involved chemical mechanisms is given. AZs being high performance photoinitiators, their use in new cationic LED 3D printing resins will be also presented, that is, the cationic process upon LED projector @405 nm can be useful to reduce the shrinkage usually observed for radical polymerization. LED projector printing is very interesting compared to laser writing as this technology projects the profile of an entire layer of a 3D object at one time. [ABSTRACT FROM AUTHOR]

A series of conjugated polymers and oligomers previously used in organic photovoltaics and organic light-emitting diodes (OLEDs) have been examined for the first time as photoinitiators of polymerization. They address the present and future challenges facing photopolymerization: requirement of high extinction molar coefficients, absorption over the whole visible spectrum, ability to easily withdraw or release electrons. Interestingly, these compounds initiate the cationic polymerization of epoxides or the free radical polymerization of acrylates upon exposure of the photocurable formulations to a LED emitting at 405 nm. Some of them can potentially operate under blue, green, or red laser diodes. [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]

Five novel thioxanthone (TX)-functionalized methacrylates as copolymerizable photoinitiators (CopPIs) for polymerization of acrylates are synthesized from reactions of tert-butyl α-bromomethacrylate with 2-hydroxy thioxanthone (TX1) and 1,4-dihydroxy thioxanthone (TX3), cleavage of their respective tert-butyl ester groups with trifluoroacetic acid (TX2, TX4), and by reaction of the acid chloride derivative of TX2 with Irgacure 2959 (TX5). These CopPIs absorb in the near UV-visible region (390-420 nm; absorption redshift =10-40 nm, ε values comparable to TX). Their performances are studied under LED exposure at 385 and 405 nm using real-time FTIR. The reactivities of TX1 and TX2 are similar to isopropyl thioxanthone, used as reference; and TX4 have lower reactivities, due to their difunctionality, which however makes them good crosslinking agents. TX5 is the first monomeric PI possessing two different type side-chain photoinitiating groups. The migration stability of two of these CopPIs is shown in the cured polyacrylates. The photochemical mechanisms are studied by electron spin resonance, steady state photolysis, laser flash photolysis, and cyclic voltammetry. [ABSTRACT FROM AUTHOR]

The photochemical and electrochemical investigations of commercially available, safe, and cheap fluorescent brighteners, namely, triazinylstilbene (commercial name: fluorescent brightener 28) and 2,5-bis(5-tert-butyl-benzoxazol-2-yl)thiophene, as well as their original use as photoinitiators of polymerization upon light emitting diode (LED) irradiation are reported. Remarkably, their excellent near-UV-visible absorption properties combined with outstanding fluorescent properties allow them to act as high-performance photoinitiators when used in combination with diaryliodonium salt. These two-component photoinitiating systems can be employed for free radical polymerizations of acrylate. In addition, this brightener-initiated photopolymerization is able to overcome oxygen inhibition even upon irradiation with low LED light intensity. The underlying photochemical mechanisms are investigated by electron-spin resonance-spin trapping, fluorescence, cyclic voltammetry, and steady-state photolysis techniques. [ABSTRACT FROM AUTHOR]

ABSTRACT The cations and radicals produced in aminothiazonaphthalic anhydride derivatives (ATNAs) combined with an iodonium salt, N-vinylcarbazole, amine, or chloro triazine initiate the ring-opening cationic polymerization of epoxides and the free radical polymerization of acrylates under LEDs at 405 or 455 nm. The photoinitiating ability of these novel photoinitiating systems is higher than that of the well-known camphorquinone-based systems. An example of the high reactivity of the new proposed photoinitiator is also provided in resins for 3D-printing using a LED projector@405 nm. The chemical mechanisms are investigated by steady-state photolysis, cyclic voltammetry, fluorescence, laser flash photolysis, and electron spin resonance spin-trapping techniques. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 1189-1196 [ABSTRACT FROM AUTHOR]

ABSTRACT Only one naphthalic anhydride derivative has been reported as light sensitive photoinitiator, this prompted us to further explore the possibility to prepare a new family of photoinitiators based on this scaffold. Therefore, eight naphthalic Naphthalic anhydride derivatives (ANH1-ANH8) have been prepared and combined with an iodonium salt (and optionally N-vinylcarbazole) or an amine (and optionally 2,4,6- tris(trichloromethyl)-1,3,5-triazine) to initiate the cationic polymerization of epoxides and the free radical polymerization of acrylates under different irradiation sources, that is, very soft halogen lamp (∼ 12 mW cm−2), laser diode at 405 nm (∼1.5 mW cm−2) or blue LED centered at 455 nm (80 mW cm−2). The ANH6 based photoinitiating systems are particularly efficient for the cationic and the radical photopolymerizations, and even better than that of the well-known camphorquinone based systems. The photochemical mechanisms associated with the chemical structure/photopolymerization efficiency relationships are studied by steady state photolysis, fluorescence, cyclic voltammetry, laser flash photolysis, and electron spin resonance spin-trapping techniques. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 2860-2866 [ABSTRACT FROM AUTHOR]

A small library of triazolylidene-boranes that differ only in the nature of the aryl group on the external nitrogen atom was prepared. Their reactivity as hydrogen-atom donors, as well as that of the corresponding N-heterocyclic carbene (NHC)-boryl radicals toward methyl acrylate and oxygen, was investigated by laser flash photolysis, molecular orbital calculations, and ESR spin-trapping experiments, and benchmarked relative to the already known dimethyltriazolylidene-borane. The new NHC-boranes were also used as co-initiators for the Type I photopolymerization of acrylates. This allowed a structure-reactivity relationship with regard to the substitution pattern of the NHC to be established and the role of electronic effects in the reactivity of NHC-boryl radicals to be probed. Although their rate of addition to methyl acrylate depends on their electronegativity, the radicals are all nucleophilic and good initiators for photopolymerization reactions. [ABSTRACT FROM AUTHOR]

Naphthalimide derivatives (NDAs) with amino- or alkylthio-substituents have been synthesized and combined in photoinitiating systems (PIS) with an iodonium salt, N-vinylcarbazole, an amine, or 2,4,6- tris(trichloromethyl)-1,3,5-triazine to produce radicals, cation radicals, or cations. The photochemical mechanisms are investigated by fluorescence, cyclic voltammetry, laser flash photolysis, electron spin resonance spin trapping, and steady state photolysis techniques. The generated reactive species are capable of initiating the cationic polymerization (CP) of epoxides under air or the free radical polymerization (FRP) of acrylates in laminate upon exposure to visible lights delivered by a halogen lamp, a cold white light-emitting diode (LED), or LEDs at 385, 395, 405, 455, or 470 nm. Compared to the well-known camphorquinone based systems, the novel NDA containing PISs exhibit higher efficiencies both for CP and FRP. Remarkably, the photo­bleaching of some NDAs is significant, and colorless final polymer coatings are obtained. The structure/photochemical property relationships of NDAs are discussed in detail (redox potentials, fluorescence, rate constants of reactions, etc.) to shed some light on their respective photoinitiating ability. [ABSTRACT FROM AUTHOR]

ABSTRACT Isoquinolinone derivatives bearing amino- or nitro- substituent (IQNs) have been synthesized as photoinitiators and combined with various additives (i.e., iodonium salt, N-vinylcarbazole, amine or 2,4,6- tris(trichloromethyl)−1,3,5-triazine) to initiate ring-opening cationic polymerizations (CP) or free radical polymerizations under exposure to visible LEDs (e.g., LEDs at 405 nm or 455 nm, or cold white LED) or a halogen lamp. Compared to the well-known camphorquinone-based systems, the novel IQNs-based combinations employed here demonstrate higher efficiencies for the CP of epoxides. The photochemically generated reactive species (i.e., cations and radicals) from the IQNs-based systems have been investigated by steady state photolysis, cyclic voltammetry, fluorescence, laser flash photolysis, and electron spin resonance spin trapping techniques. The structure/reactivity/photoinitiating ability relationships of IQNs-based combinations are also discussed; the crucial role of the excited state lifetimes of the photoinitiators to ensure efficient quenching by additives is clearly underlined. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 1806-1815 [ABSTRACT FROM AUTHOR]

ABSTRACT N, N'-dibutylquinacridone (DBQA) is utilized here for the first time as a high-performance panchromatic photoinitiator for the cationic polymerization (CP) of epoxides, the free radical polymerization (FRP) of acrylates, the thiol-ene polymerization and the synthesis of interpenetrated polymer networks (epoxide/acrylate) under violet, blue, green and yellow lights (emitted from LED at 405 nm, 470 nm, 520 nm, or 594 nm, or laser diode at 532 nm). It confers a panchromatic character to the photopolymerizable matrices. Remarkably, the proposed DBQA based photoinitiating systems exhibit quite excellent efficiency (the final monomer conversion for multifunctional monomers at room temperature can reach 62% and 50% in CP and FRP, respectively) and appear as much more powerful than the camphorquinone or Eosin-Y containing reference systems for visible light. For green light, DBQA is much more reactive than the literature reference (Eosin-Y) and for blue light, a good reactivity is found compared with camphorquinone. The photochemical mechanisms are studied by molecular orbital calculations, steady state photolysis, fluorescence, cyclic voltammetry, laser flash photolysis, and electron spin resonance spin trapping techniques. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 1719-1727 [ABSTRACT FROM AUTHOR]

ABSTRACT Naphthalimide-phthalimide derivatives (NDPDs) have been synthesized and combined with an iodonium salt, N-vinylcarbazole, amine or 2,4,6-tris(trichloromethyl)-1,3,5-triazine to produce reactive species (i.e., radicals and cations). These generated reactive species are capable of initiating the cationic polymerization of epoxides and/or the radical polymerization of acrylates upon exposure to very soft polychromatic visible lights or blue lights. Compared with the well-known camphorquinone based systems used as references, the novel NDPD based combinations employed here demonstrate clearly higher efficiencies for the cationic polymerization of epoxides under air as well as the radical polymerization of acrylates. Remarkably, one of the NDPDs (i.e., NDPD2) based systems is characterized by an outstanding reactivity. The structure/reactivity/efficiency relationships of the investigated NDPDs were studied by fluorescence, cyclic voltammetry, laser flash photolysis, electron spin resonance spin trapping, and steady state photolysis techniques. The key parameters for their reactivity are provided. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 665-674 [ABSTRACT FROM AUTHOR]

ABSTRACT Isoquinolinone derivatives (IQ) have been synthesized and combined with different additives (an amine, 2,4,6- tris(trichloromethyl)-1,3,5-triazine, an iodonium salt, or N-vinylcarbazole) to produce reactive species (i.e. radicals and cations) being able to initiate the radical polymerization of acrylates, the cationic polymerization of epoxides, the thiol-ene polymerization of trifunctional thiol/divinylether, and the synthesis of epoxide/acrylate interpenetrated polymer network IPN upon exposure to very soft polychromatic visible lights, blue laser diode or blue LED lights. Compared with the use of camphorquinone based systems, the novel combinations employed here ensures higher monomer conversions (∼50-60% vs. ∼15-35%) and better polymerization rates in radical polymerization. The chemical mechanisms are studied by steady-state photolysis, fluorescence, cyclic voltammetry, laser flash photolysis, and electron spin resonance spin trapping techniques. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 567-575 [ABSTRACT FROM AUTHOR]

ABSTRACT A benzophenone-naphthalimide derivative (BPND) bearing tertiary amine groups has been developed as a high-performance photoinitiator in combination with 2,4,6- tris(trichloromethyl)-1,3,5-triazine or an iodonium salt for both the free radical polymerization (FRP) of acrylates and the cationic polymerization (CP) of epoxides upon exposure to near UV and visible LEDs (385-470 nm). BPND can even produce radicals without any added hydrogen donor. The photochemical mechanisms are studied by molecular orbital calculations, steady state photolysis, electron spin resonance spin trapping, fluorescence, cyclic voltammetry and laser flash photolysis techniques. These novel BPND based photoinitiating systems exhibit an efficiency higher than that of the well-known camphorquinone-based systems (FRP and CP) or comparable to that of bis(2,4,6-trimethylbenzoyl)-phenylphosphineoxide (FRP at λ ≤ 455 nm). © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 445-451 [ABSTRACT FROM AUTHOR]

Two star-shaped tris(4-(thiophen-2-yl)phenyl)amine derivatives, namely tris(4-(5-(3-pentylthieno[3,2- b]thiophen-5-yl)thiophen-2-yl)phenyl)amine and tris(4-(5-(3-pentyl-2-(thiophen-2-yl)thieno[3,2- b]thiophen-5-yl)thiophen-2-yl)phenyl)amine, are developed as photoinitiators for radical and cationic polymerizations under near-UV and visible light-emitting diodes (LEDs) (e.g., 385, 405, and 455 nm). When used in combination with an iodonium salt (and optionally N-vinyl carbazole) or an amine/alkyl halide couples, they lead to excellent photoinitiating abilities for the polymerization of epoxides or (meth)acrylates under air. Compared with commercial photoinitiators, i.e., camphorquinone-based systems or bis(2,4,6-trimethylbenzoyl)-phenylphosphineoxide, the novel photoinitiators exhibit noticeably higher polymerization efficiencies under air (epoxide conversions = 41-57% vs ≈0%, halogen lamp exposure; methacrylate conversions = 50-55% vs 44%, LED at 405 nm exposure; methacrylate conversions = 34-42% vs 0-8%, LED at 455 nm exposure). These systems are also interesting in overcoming oxygen inhibition. The photochemical mechanisms are studied by steady-state photolysis, electron spin resonance spin trapping, fluorescence, cyclic voltammetry, and laser flash photolysis techniques. [ABSTRACT FROM AUTHOR]

An iridium(III) complex comprising three different cyclometalated phenylpyridine-based ligands was designed and synthesized. Interestingly, mixed-ligand complexes could be obtained by using a simple and straightforward procedure. A tris(heteroleptic) IrIII complex was obtained as a mixture of stereoisomers that could not be separated. Photophysical properties of the tris(heteroleptic) complex was investigated by UV/VIS absorption and luminescence spectroscopy, and compared with those of the parent homoleptic complexes. Modelling by time-dependent density functional theory (TD-DFT) was also performed to elucidate the nature and the location of the excited state, and to support the experimental results. [ABSTRACT FROM AUTHOR]

Four new push-pull dyes derived from Michler's ketones are investigated. These dyes, based on a donor-π-acceptor (D-π-A) structure, exhibit a tunable character according to the electron-withdrawing ability of the acceptor used. The new proposed structures can be used in high-performance photoinitiating systems. Remarkably, two of them are characterized by an excellent reactivity to initiate the free-radical polymerization of acrylates, the ring-opening polymerization of epoxides, as well as the synthesis of interpenetrating polymer networks (IPNs) under exposure to a laser diode at 457 nm. The chemical mechanisms are investigated by steady-state photolysis, fluorescence, and electron spin-resonance (ESR) experiments. [ABSTRACT FROM AUTHOR]

Ten acridinediones (ADs) with different substituents are prepared and investigated for their abilities to initiate a ring-opening cationic photopolymerization in combination with an iodonium salt and N-vinylcarbazole upon UV-vis light (Xe-Hg lamp; >330 nm) or visible light (halogen lamp) exposure. The structural effects in the ADs are outlined. The cationic and radical photopolymerization of an epoxide/acrylate blend in a one-step hybrid cure very efficiently leads to the formation of an interpenetrated polymer network under UV-vis light or visible light irradiation (30 s for tack-free coatings). The photochemical mechanisms are studied by molecular orbital calculations, steady-state photolysis, electron spin resonance-spin trapping, cyclic voltammetry, fluorescence, and laser flash photolysis techniques. [ABSTRACT FROM AUTHOR]

Truxene-acridine-1,8-dione derivatives ( Tr_AD) are proposed as new photoinitiators of polymerization under very soft irradiation (by a household halogen lamp), as well as laser-diode exposure at 405 nm. They exhibit a strong absorption around 380 nm. The Tr_AD/diphenyl iodonium salt/9-vinylcarbazole combination is able to promote the ring-opening polymerization of an epoxide, whereas the Tr_AD/alkyl halide/amine system is very efficient in initiating the radical photopolymerization of an acrylate. Excellent polymerization profiles are obtained. Acrylate/epoxide blends are also easily polymerized. These Tr_ADs in the three-component systems behave as photocatalysts according to oxidative cycles. The mechanisms are discussed for the different multicomponent initiating systems. [ABSTRACT FROM AUTHOR]

Nine different perylene derivatives are prepared and their ability to initiate, when combined with an iodonium salt (and optionally N-vinylcarbazole), a ring-opening cationic photopolymerization of epoxides under very soft halogen lamp irradiation is investigated. One of them is particularly efficient under a red laser diode exposure at 635 nm and belongs now to the very few systems available at this wavelength. The photochemical mechanisms are studied by steady-state photolysis, electron spin resonance spin trapping, fluorescence, cyclic voltammetry, and laser flash photolysis techniques. [ABSTRACT FROM AUTHOR]

New photoinitiating systems based on a polyoxometalate (POM) are proposed: phosphomolybdic acid in combination with silane, germane, or iodonium salt can be used to generate silyl, germyl, or phenyl radicals as well as silylium cations. The photochemical mechanisms are studied by steady-state photolysis and electron spin resonance. The phosphomolybdic acid/silane/iodonium salt system can initiate either the radical photopolymerization of acrylates or the cationic photopolymerization of epoxides. The synthesis of interpenetrated polymer networks can also be carried out. The mechanical properties of the synthesized polymers are affected by the presence of POM in the matrix, as shown by their dynamic mechanical analysis (DMA). [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]

New thiols for efficient thiol-ene polymerization reactions are presented. They do not exhibit any unpleasant odor, are characterized by quite good light-absorption properties at λ > 300 nm, and generate thiyl radicals upon UV-light exposure. Due to these interesting properties and contrary to many previously reported methodologies, the present thiol-acrylate polymerizations can be efficiently carried out without the presence of any additional photoinitiator. The chemical mechanisms are investigated by steady-state photolysis and electron spion resonance (ESR) experiments. Important parameters can also be extracted from molecular orbital calculations. [ABSTRACT FROM AUTHOR]

New perylene-3,4:9,10-bis(dicarboximide) (PBI) photoinitiators/photosensitizers derived from perylene-3,4:9,10-tetracarboxylic dianhydride are synthesized and investigated for the formation of free radicals under air and under very soft irradiation (i.e., halogen lamp) or laser diode exposure at 532 nm. Such a PBI in combination with a diphenyl iodonium salt and N-vinylcarbazole or a silane very efficiently promotes the ring-opening polymerization of epoxides and can also generate acrylate/epoxide interpenetrated polymer networks. It partly behaves as a metal-free organic photocatalyst operating in an oxidative catalytic cycle. The different chemical intermediates are characterized by ESR and laser flash photolysis experiments. The mechanisms involved in the initiation step are discussed. [ABSTRACT FROM AUTHOR]

Two new photoinitiators with unprecedented light absorption properties are proposed on the basis of a suitable truxene skeleton where several UV photoinitiators PI units such as benzophenone and thioxanthone are introduced at the periphery and whose molecular orbitals MO can be coupled with those of the PI units: a red-shifted absorption and a strong increase of the molecular extinction coefficients (by a ≈ 20-1000 fold factor) are found. These compounds are highly efficient light-harvesting photoinitiators. The scope and practicality of these photoinitiators of polymerization can be dramatically expanded, that is, both radical and cationic polymerization processes are accessible upon very soft irradiation conditions (halogen lamp, LED...︁) thanks to the unique light absorption properties of the new proposed structures. [ABSTRACT FROM AUTHOR]