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

New Donor-Acceptor Stenhouse Adducts as Visible and Near Infrared Light Polymerization Photoinitiators

Polymerization photoinitiators that can be activated under low light intensity and in the visible range are being pursued by both the academic and industrial communities. To efficiently harvest light and initiate a polymerization process, dyes with high molar extinction coefficients in the visible range are ideal candidates. In this field, Donor-acceptor Stenhouse Adducts (DASA) which belong to a class of recently discovered organic photochromic molecules still lack practical applications. In this work, a series of DASA-based dyes are proposed as photoinitiators for the free radical polymerization of (meth)acrylates upon exposure to a near infrared light (laser diode at 785 nm)

Frontier research in radical initiating systems : photoredox catalysis as a new strategy for polymer synthesis

Ces dernières années, la photopolymérisation a fait l'objet d'intenses efforts de recherche en raison de la croissance constante des applications industrielles. C’est un processus rapide pouvant être réalisée à température ambiante, sans solvant et permettant d'obtenir un contrôle spatial et temporel de la polymérisation. Ces dernières années, l'utilisation de conditions d'irradiation douce qui constitue une alternative aux procédés de photopolymérisation UV à l'origine de nombreux soucis de sécurité est activement recherchée. Par conséquent, le développement de nouveaux systèmes photoamorceurs absorbant fortement dans la région visible ou du proche infra-rouge sont activement recherchés par les communautés académiques et industrielles. Néanmoins, même si certains résultats sont prometteurs, les systèmes reportés sont souvent caractérisés par des réactivités modérées et rivalisent difficilement avec les systèmes UV actuels. Dans ce contexte, nous avons synthétisé une large librairie de molécules photosensibles capables d’absorber la lumière dans le domaine du visible ou du proche infrarouge et capables d’amorcer une réaction de polymérisation avec un système photoamorceur basée sur la catalyse photoredox. Dans ce manuscrit, nous présentons aussi bien la synthèse et les capacités de polymérisation de différentes familles de colorants. Leurs propriétés photochimiques ont également été étudiées par spectrométrie UV-visible, luminescence, photolyse, surveillance de la température et expériences de résonance paramagnétique électronique. Des applications telles que l'impression 3D et les expériences d'écriture laser sont également présentéesIn recent years, photopolymerization has been the subject of intense research efforts due to the constant growth of industrial applications. It is a quick process that can be performed at room temperature, solvent-free conditions and enables to get a spatial and a temporal control of the polymerization process. In recent years, the use of irradiation conditions that constitutes an alternative to the UV photopolymerization processes at the origin of numerous safety concerns are actively researched. Therefore, the development of new photoinitiating systems which absorb strongly in the visible or near infrared region are actively researched by both the academic and industrial communities. Nevertheless, even if some results are promising, the reported systems are often characterized by moderate reactivities and hardly compete with current UV systems. In this context, we have synthesized a large library of photosensitive molecules capable of absorbing light in the visible or near infrared range and capable of initiating a polymerization reaction with a photoinitiating system based on photoredox catalysis. In this manuscript, we present both the synthesis and the polymerization abilities of different families of dyes. Their photochemical properties were also studied by UV-Visible spectrometry, luminescence, photolysis, temperature monitoring and electronic paramagnetic resonance experiments. Applications such as 3D printing and laser write experiments are also presente

Recent Advances on Copper Complexes as Visible Light Photoinitiators and (Photo) Redox Initiators of Polymerization

International audienceMetal complexes are used in numerous chemical and photochemical processes in organic chemistry. Metal complexes have not been excluded from the interest of polymerists to convert liquid resins into solid materials. If iridium complexes have demonstrated their remarkable photochemical reactivity in polymerization, their high costs and their attested toxicities have rapidly discarded these complexes for further developments. Conversely, copper complexes are a blooming field of research in (photo) polymerization due to their low cost, easy syntheses, long-living excited state lifetimes, and their remarkable chemical and photochemical stabilities. Copper complexes can also be synthesized in solution and by mechanochemistry, paving the way towards the synthesis of photoinitiators by Green synthetic approaches. In this review, an overview of the different copper complexes reported to date is presented. Copper complexes are versatile candidates for polymerization, as these complexes are now widely used not only in photopolymerization, but also in redox and photoassisted redox polymerization processes

Recent advances on naphthalic anhydrides and 1,8-naphthalimide-based photoinitiators of polymerization

International audienceThe design of photoinitiators of polymerization is an active research field and the development of initiators activable in the visible range and under low light intensity have been the focus of numerous research efforts from both the academic and industrial communities. Recently, two families of polyaromatic compounds, i.e. 1,8-naphthalic anhydride and naphthalimides, have been extensively studied by different research groups due to their easiness of synthesis and the possibility to easily tune the photophysical properties. Especially, panchromatic, crosslinkable or water-soluble photoinitiators could be easily developed starting from the benchmark and cheap 1,8-naphthalic anhydride. In this review, an overview of the different photoinitiators based on naphthalic anhydride or the naphthalimide scaffold is presented. Based on the diversity of structures reported in the literature, a structure-performance relationship could be established in this review

Recent Advances on Nitrofluorene Derivatives: Versatile Electron Acceptors to Create Dyes Absorbing from the Visible to the Near and Far Infrared Region

WOS:000456419200083Push-pull dyes absorbing in the visible range have been extensively studied so that a variety of structures have already been synthesized and reported in the literature. Conversely, dyes absorbing in the near and far infrared region are more scarce and this particularity relies on the following points: difficulty of purification, presence of side-reaction during synthesis, low availability of starting materials, and low reaction yields. Over the years, several strategies such as the elongation of the pi-conjugated spacer or the improvement of the electron-donating and accepting ability of both donors and acceptors connected via a conjugated or an aliphatic spacer have been examined to red-shift the absorption spectra of well-established visible dyes. However, this strategy is not sufficient, and the shift often remains limited. A promising alternative consists in identifying a molecule further used as an electron-accepting group and already presenting an absor ption band in the near infrared region and to capitalize on its absorption to design near and far infrared absorbing dyes. This is the case with poly(nitro)fluorenes that already exhibit such a contribution in the near infrared region. In this review, an overview of the different dyes elaborated with poly(nitro)fluorenes is presented. The different applications where these different dyes have been used are also detailed

Photoinitiators of polymerization with reduced environmental impact: Nature as an unlimited and renewable source of dyes

International audienceThe development of new procedures aiming at reducing the environmental impact of polymerization processes is a major societal issue. In this field, light-assisted polymerization and especially visible light photopolymerization can address this issue by enabling in the future, Sun, to be used as the irradiation source. Presently, numerous visible light photoinitiators (xanthene dyes, porphyrins and phthalocyanines) are used in industry but their toxicities constitute a major issue for future uses of polymers. Therefore, photopolymerization is facing a short-term challenge and the development of visible light photoinitiators of polymerization has become a blooming field of research during the last decade. An ever-growing effort is thus done to develop new structures, effort which is also supported by the recent applications of photopolymerization in 3D-printing. Depending on the applications, use of synthetic photoinitiators can constitute a severe limitation for future applications of photopolymers so that the use of natural products has been identified as a promising alternative to address the toxicity or the biocompatibility issues. In this review, an overview of the different visible-light photoinitiators based on natural products is provided

Ferrocene: An unrivaled electroactive building block for the design of push-pull dyes with near-infrared and infrared absorptions

WOS:000478711200061International audienceFerrocene is an exceptional building block for the development of dyes with reversible redox properties. Dyes absorbing int the near infrared and infrared region are actively researched due to their potential applications ranging from telecommunication to defence systems. In this review, an overview of the different NIR and infrared dyes reported to date is presented. Parallel to the photophysical characteristics, the synthetic pathways giving access to these structures is presented

Recent advances on push–pull organic dyes as visible light photoinitiators of polymerization

International audiencePhotoinitiators activable under visible light and low light intensity are actively researched as it can advantageously address the safety concerns raised by the traditional UV-light photopolymerization process as well as the light penetration issue. Among dyes strongly absorbing in the visible range, one of the most promising family of photoinitiators are push-pull dyes based on an electron-donating and an electron-accepting moiety connected at both ends of a polyenyl-type spacer. By acting on both the strength of the electron donor and the electron accep-tor, position of the intramolecular charge transfer (ICT) band can be easily tuned from the near-UV to the near infrared region. In this review, an overview of the different D-π-A push-pull dyes used as visible photoinitiators of polymerization is presented. Over the years, a clear evolution in the chemical structure of the electron accep-tors can be clearly observed, evidencing the strong activity existing around these structures

Organometallic vs organic photoredox catalysts for photocuring reactions in the visible region

WOS:000453278400001Recent progresses achieved in terms of synthetic procedures allow now the access to polymers of well-defined composition, molecular weight and architecture. Thanks to these recent progresses in polymer engineering, the scope of applications of polymers is far wider than that of any other class of material, ranging from adhesives, coatings, packaging materials, inks, paints, optics, 3D printing, microelectronics or textiles. From a synthetic viewpoint, photoredox catalysis, originally developed for organic chemistry, has recently been applied to the polymer synthesis, constituting a major breakthrough in polymer chemistry. Thanks to the development of photoredox catalysts of polymerization, a drastic reduction of the amount of photoinitiators could be achieved, addressing the toxicity and the extractability issues; high performance initiating abilities are still obtained due to the catalytic approach which regenerates the catalyst. As it is a fast-growing field , this review will be mainly focused on an overview of the recent advances concerning the development of organic and organometallic photoredox catalysts for the photoreticulation of multifunctional monomers for a rapid and efficient access to 3D polymer networks