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

European Polymer Journal

2020

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With regards to the environmental and safety concerns raised nowadays by the polymer industry, polymerization processes requiring light as the activation source are currently knowing a revival of interest after decades of disinterest. Recent progresses in photopolymerization are notably sustained by the development of new polymerization application namely 3D and 4D printing enabling an unprecedented access to structures of incredible complexity. Parallel to the manufacturing process, the polymer material itself and its composition are also facing numerous questions concerning their environmental and human health impacts. Beyond the monomers, the different additives introduced in the resin can also be potentially toxic so that a great deal of efforts is currently done to develop new photoinitiators with a toxicity assessed as being insignificant. In this field, iron-based metal complexes are candidates of choice due to the clinical demonstration of their very low toxicities. Among iron complexes, ferrocene is among the most widely studied iron-based metallocene. Due to its unique and reversible electrochemical properties as well as their absorption centred in the visible range, numerous photoinitiators have been developed with ferrocene or its oxidized form i.e. ferrocenium. Parallel to this, the remarkable electrochemical properties of ferrocenium made it an excellent candidate for its incorporation in photoinitiating systems. However, interest for iron-based photoinitiators was not limited to ferrocene and ferrocenium, and Schiff base complexes were also successfully used as initiators of polymerization. In this review, an overview of the different iron-based photoinitiating systems reported to date is presented. More precisely, if iron-based photoinitiators are developed since 50 years, a special focus will be done on photoinitiators designed for recent polymerization conditions, namely, under visible light and low light intensity.

Section: Ferrocene-based Push-pull Dyesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Recent advances on iron-based photoinitiators of polymerization

European Polymer Journal

2020

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“…A series of nine dyes, namely Fe-23-Fe-31, was examined for photopolymerization carried out at 405 and 785 nm (see Figure 28). NIR dyes based on ferrocene have been extensively studied in the literature due to the reversibility of the oxidation process centered on the ferrocene moiety [154]. Concerning iron complexes, ferrocene which is one of the simplest metallocene comprising an iron (II) cation sandwiched between two cyclopentadienyl moieties was notably used in 2019 for the design of a series of push-pull dyes capable of initiating a polymerization in the near-infrared region (NIR) [153].…”

Section: Iron Complexesmentioning

confidence: 99%

“…A series of nine dyes, namely Fe-23-Fe-31, was examined for photopolymerization carried out at 405 and 785 nm (see Figure 28). NIR dyes based on ferrocene have been extensively studied in the literature due to the reversibility of the oxidation process centered on the ferrocene moiety [154]. From a synthetic point of view, push-pull chromophores are interesting compounds as these structures can be easily synthesized in one ste, by means of a Knoevenagel reaction.…”

Section: Iron Complexesmentioning

confidence: 99%

Recent Advances on Visible Light Metal-Based Photocatalysts for Polymerization under Low Light Intensity

2019

Catalysts

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In recent years, polymerization processes activated by light have attracted a great deal of interest due to the wide range of applications in which this polymerization technique is involved. Parallel to the traditional industrial applications ranging from inks, adhesives, and coatings, the development of high-tech applications such as nanotechnology and 3D-printing have given a revival of interest to this polymerization technique known for decades. To initiate a photochemical polymerization, the key element is the molecule capable to interact with light, i.e., the photoinitiator and more generally the photoinitiating system, as a combination of several components is often required to create the reactive species responsible for the polymerization process. With the aim of reducing the photoinitiator content while optimizing the polymerization yield and/or the polymerization speed, photocatalytic systems have been developed, enabling the photosensitizer to be regenerated during the polymerization process. In this review, an overview of the photocatalytic systems developed for polymerizations carried out under a low light intensity and visible light is provided. Over the years, a wide range of organometallic photocatalysts has been proposed, addressing both the polymerization efficiency and/or the toxicity, as well as environmental issues.

“…Parallel to their short-lived excited state lifetimes, the low photochemical stability of the Schiff Base ligands, their averred instability under acidic conditions also made this second family of complex a series of metal complexes of poor interest for photoinitiation [51]. However, recently, stability of iron complexes was addressed with the development of ferrocene derivatives, this metallocene being well-known for its remarkable thermal, chemical, electrochemical, and photochemical stability [52,53]. Among metals that could be used to design relatively cheap complexes with long-living excited states, copper can be cited as a relevant example [54][55][56][57][58][59][60][61].…”

Section: Introductionmentioning

confidence: 99%

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

Noirbent

2020

Catalysts

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Metal 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.