Disubstituted Aminoanthraquinone-Based Multicolor Photoinitiators: Photoinitiation Mechanism and Ability of Cationic Polymerization under Blue, Green, Yellow, and Red LEDs

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.P.X. acknowledges funding from the Australian Research Council Future Fellowship (FT170100301). M.L.C. gratefully acknowledges a Georgina Sweet ARC Laureate Fellowship (FL170100041) and generous allocations of supercomputing time on the National Facility of the Australian National Computational Infrastructur

Photochemistry and Radical Chemistry under Low Intensity Visible Light Sources: Application to Photopolymerization Reactions:

The search for radical initiators able to work under soft conditions is a great challenge, driven by the fact that the use of safe and cheap light sources is very attractive. In the present paper, a review of some recently reported photoinitiating systems for polymerization under soft conditions is provided. Different approaches based on multi-component systems (e.g., photoredox catalysis) or light harvesting photoinitiators are described and discussed. The chemical mechanisms associated with the production of free radicals usable as initiating species or mediators of cations are reported

Monocomponent photoinitiators based on benzophenone-carbazole structure for LED photoinitiating systems and application on 3D printing

In this article, different substituents (benzoyl, acetyl, styryl) are introduced onto the carbazole scaffold to obtain 8 novel carbazole derivatives. Interestingly, a benzoyl substituent, connected to a carbazole group, could form a benzophenone moiety, which composes a monocomponent Type II benzophenone-carbazole photoinitiator (PI). The synergetic effect of the benzophenone moiety and the amine in the carbazole moiety is expected to produce high performance photoinitiating systems (PISs) for the free radical photopolymerization (FRP). For different substituents, clear effects on the light absorption properties are demonstrated using UV-Visible absorption spectroscopy. Benzophenone-carbazole PIs can initiate the FRP of acrylates alone (monocomponent Type II photoinitiator behavior). In addition, fast polymerization rates and high function conversions of acrylate are observed when an amine and/or an iodonium salt are added in systems. Benzophenone-carbazole PIs have good efficiencies in cationic photopolymerization (CP) upon LED @ 365 nm irradiation in the presence of iodonium salt. In contrast, other PIs without synergetic effect demonstrate unsatisfied photopolymerization profiles in the same conditions. The best PIS identified for the free radical photopolymerization were used in three-dimensional (3D) printing. Steady state photolysis and fluorescence quenching experiments were carried out to investigate the reactivity and the photochemistry and photophysical properties of PIs. The free radicals, generated from the studied PISs, are detected by the electron spin resonance - spin trapping technique. The proposed chemical mechanisms are provided and the structure/reactivity/efficiency relationships are also discussed. All the results showed that the benzophenone-carbazole PIs have a good application potential, and this work provides a rational design route for PI molecules. Remarkably, BPC2-BPC4, C6, C8 were never synthetized before; therefore, 5 of the 8 compounds are completely new

Analyse de contours rotationnels de bandes d'absorption vibroniques de cations aromatiques formes par ionisation multiphotonique resonnante: distribution rotationnelle non boltzmanienne

SIGLEINIST T 73601 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Role of Thiol Oxidation by Air in the Mechanism of the Self-Initiated Thermal Thiol-ene Polymerization

International audienceA spontaneous thiol-ene polymerization has been reported in the literature for a broad range of monomers, generally under conditions avoiding solvent, heating and the intentional formation of radicals. In the search for a mechanism accountable to self-initiated thiol-ene polymerization, this study demonstrates the significant role played by thiyl radicals produced by thiol oxidation through dissolved atmospheric oxygen in the thiol-ene mixture. To determine the factors underlying the reactivity, self-initiated polymerization kinetics, thiol solvation and the nature of initiating radicals are studied by means of various techniques including real-time FTIR, 1 H NMR spectroscopy and spin-trapping experiments. Our data support that the driving force for thiol air oxidation is the polarization of the S-H bond. Thiol substituents with electron-withdrawing properties and/or hydrogen-bonded thiol-solvent (or thiol-alkene) complexes favor self-initiation by increasing S-H bond polarization, thereby easing an electron transfer to molecular oxygen

Photogenerating Silver Nanoparticles and Polymer Nanocomposites by Direct Activation in the Near Infrared

This work reports on an improvement of the photochemically assisted synthesis of silver nanoparticles by direct photoreduction of AgNO3 with a laser source emitting in the near infrared range (NIR). For this, polymethine dyes were used as the photoactive agents. Both the effects of central chain structure and activation intensity were investigated. The reduction kinetics was followed up by UV-Vis spectroscopy, and the particles size was evaluated by transmission electron microscopy. The results showed that light intensity affects both the average size and size distribution of Ag nanoparticles generated through this process. The particles can also be generated in situ in a photopolymerizable formulation so that metal/polymer nanocomposites become available through a one-step photoassisted process on the basis of NIR activation. The process described herein is very fast (seconds to a few minutes), and it readily lends itself to automatization for mass production of micro-optical elements implemented directly onto integrated NIR sources

Photopolymerization under various monochromatic UV/visible LEDs and IR lamp: Diamino-anthraquinone derivatives as versatile multicolor photoinitiators

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.P. X. acknowledges funding from the Australian Research Council Future Fellowship (FT170100301)

Photocatalyzed Cu-based ATRP involving an oxidative quenching mechanism under visible light

International audienceA new type of photocatalyzed Cu-based atom transfer radical polymerization (ATRP) is described, involving directly the light absorption of the activator form of the copper complex Cu(I). The selected catalyst was bis(1,10-phenanthroline)copper(I), Cu(phen)2+, due to its intense absorption in the visible domain, which permitted to use very soft irradiation conditions, consisting of a simple household blue LED at 0.9 W. An excellent control over the polymerization of methyl methacrylate (MMA) in dimethylformamide (DMF) was observed under irradiation in these conditions, using ethyl α-bromophenylacetate (EBPA) as the initiator, with polydispersity indexes (PDI) as low as 1.10 while using low catalyst content (80 ppm). The proposed mechanism implies first the formation under irradiation of the excited state of the activator form of the complex Cu(I)*. It can then rapidly undergo the oxidative quenching of the alkyl bromide, which results in its conversion into the deactivator form of the complex Cu(II)–Br along with the generation of a propagating radical. The setting up of the ATRP equilibrium ensues. Additionally, it was possible to complete the catalysis mechanism by adding triethylamine (TEA), which permitted a faster polymerization, thanks to a faster regeneration of the activator Cu(I). An excellent control over the polymerization was also observed in the presence of TEA, with PDI as low as 1.06. The addition of TEA allowed also to use a catalyst loading as low as 20 ppm, while maintaining a good controllability

Low-Cost and Recyclable Photocatalysts: Metal Oxide/Polymer Composites Applied in the Catalytic Breakdown of Dyes

Novel metal oxide/polymer composite photocatalysts prepared by photocuring with common metal oxide particles (ZnO or CeO2) and acrylic ester monomers have been investigated for the first time. Metal oxide particles were fully integrated with the acrylate polymer network based on the crosslink of poly ethylene glycol diacrylate (noted below as Poly-PEG) by photopolymerization upon mild light source (LED@405 nm) irradiation. The prepared metal/oxide composite showed excellent performance in the photodegradation of Acid Black dye (used as a benchmark pollutant) in an aqueous environment. Indeed, under UV lamp irradiation for 60 min, the degradation of Acid Black reached 59% and 56%, in the presence of 10 wt% ZnO/Poly-PEG and 3 wt% CeO2/poly PEG, respectively. Markedly, the new reported photocatalysts have offered much better performance over the conventional TiO2 photocatalytic material used as a control (39% degradation using 1 wt% TiO2/poly PEG). In turn, the new proposed metal oxide/polymer composites were further characterized by a range of analytical characterization methods, including the swelling test, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), dynamic mechanical analysis (DMA), UV–visible diffuse reflectance spectroscopy, and electron spin resonance analysis. The results showed that the new photocatalysts demonstrated excellent water adsorption properties, high-temperature resistance, and excellent recyclability, which were very suitable for wide application and in line with the concept of green chemistry

Metal-free, visible light mediated straigthforward access to benzo[b]phosphole oxides: synthetic and mechanistic studies

International audienc