The recent groundbreaking developments in the application of diaryliodonium salts in cross-coupling reactions has brought this class of previously underdeveloped reagents to the forefront of organic chemistry. With the advent of novel, facile, and efficient synthetic routes to these compounds, many more applications can be foreseen. Herein we provide an overview of the historical and recent advances in the synthesis and applications of diaryliodonium salts.

Diaryliodonium Salts: A Journey from Obscurity to Fame

The story of the discovery and development of onium salt photoinitiators for cationic polymerization is chronicled. The chemistry of the synthesis of these compounds is outlined, and the mechanisms of their initiation are discussed briefly. Among the most useful of these types of photoinitiators are diaryliodonium and triarylsulfonium salts, which are used widely for photoinduced cationic crosslinking reactions. From the very beginning, onium salt photoinitiated cationic polymerizations have found use in a multitude of practical applications. Specifically discussed in this article are the use of onium salts in coatings, adhesives, printing inks, release coatings, stereolithography, holographic recording, photocurable composites, and microelectronic photoresists. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4241–4254, 1999

https://onlinelibrary.wiley.com/doi/pdf/10.1002/%28SICI%291099-0518%2819991201%2937%3A23%3C4241%3A%3AAID-POLA1%3E3.0.CO%3B2-R

The discovery and development of onium salt cationic photoinitiators

Microfluidics is an evolving scientific field with immense commercial potential: analytical applications, such as biochemical assay development, biochemical analysis and biosensors as well as chemical synthesis applications essentially require microfluidics for sample handling, treatment or readout. A number of techniques are available to create microfluidic structures today. On industrial scale replication techniques such as injection molding are the gold standard whereas academic research mostly focuses on replication by casting of soft elastomers such as polydimethylsiloxane (PDMS). Both of these techniques require the creation of a replication master thus creating the microfluidic structure only in the second process step—they can therefore be termed two-(or multi-)step manufacturing techniques. However, very often the number of pieces to be created of one specific microfluidic design is low, sometimes even as low as one. This raises the question if two-step manufacturing is an appropriate choice, particularly if short concept-to-chip times are required. In this case one-step manufacturing techniques that allow the direct creation of microfluidic structures from digital three-dimensional models are preferable. For these processes the number of parts per design is low (sometimes as low as one), but quick adaptation is possible by simply changing digital data. Suitable techniques include, among others, maskless or mask based stereolithography, fused deposition molding and 3D printing. This work intends to discuss the potential and application examples of such processes with a detailed view on applicable materials. It will also point out the advantages and the disadvantages of the respective technique. Furthermore this paper also includes a discussion about non-conventional manufacturing equipment and community projects that can be used in the production of microfluidic devices.

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Let there be chip—towards rapid prototyping of microfluidic devices: one-step manufacturing processes

An emerging strategy for making ordered materials is modular construction, which connects preformed molecular subunits to neighbours through interactions of properly selected reactive sites. This strategy has yielded remarkable materials, including metal-organic frameworks joined by coordinative bonds, supramolecular networks linked by strong non-covalent interactions, and covalent organic frameworks in which atoms of carbon and other light elements are bonded covalently. However, the strategy has not yet produced covalently bonded organic materials in the form of large single crystals. Here we show that such materials can result from reversible self-addition polymerizations of suitably designed monomers. In particular, monomers with four tetrahedrally oriented nitroso groups polymerize to form diamondoid azodioxy networks that can be fully characterized by single-crystal X-ray diffraction. This work forges a strong new link between polymer science and supramolecular chemistry by showing how predictably ordered covalent or non-covalent structures can both be built using a single modular strategy.

Constructing monocrystalline covalent organic networks by polymerization

Photopolymers broadly comprise monomers, oligomers, polymers, or mixtures of the aforementioned materials that upon exposure to light undergo photochemical reactions that result in deep-seated changes in their structures which substantially modify their chemical and mechanical properties. Photopolymers may possess chromophores that provide for their intrinsic photosensitivity. Alternatively, other photosensitive molecules may be added that directly or indirectly interact with the photopolymer upon exposure to light to produce the desired property changes. Examples of various types of photopolymers will be presented in this article along with examples of their use in representative applications.

Photopolymer Materials and Processes for Advanced Technologies

The photolysis of triphenylsulfonium, tris(4-methylphenyl)sulfonium, tris(4-chlorophenyl)sulfonium, several monosubstituted (4-F, 4-Cl, 4-Me, 4-MeO, 4-PhS, and 4-PhCO), and disubstituted (4,4{prime}-Me{sub 2} and 4,4{prime}-(MeO){sub 2}) triphenylsulfonium salts was examined in solution. It was found that direct irradiation of triphenylsulfonium salts produced new rearrangement products, phenylthiobiphenyls, along with diphenyl sulfide, which had been previously reported. Similarly, the triarylsulfonium salts, with the exception of the (4-(phenylthio)phenyl)diphenylsulfonium salts produced new rearrangement products, phenylthiobiphenyls, along with diphenyl sulfide, which had been previously reported. Similarly, the triarylsulfonium salts, with the exception of the (4-(phenylthio)phenyl)diphenylsulfonium salts, gave the new rearrangement products. The mechanism for direct photolysis is proposed to occur from the singlet excited states to give a predominant heterolytic cleavage along with some homolytic cleavage.

Photochemistry of triarylsulfonium salts

Les produits formes par photolyse directe ou photosensibilisee sont: les dimethyl-4,4'-, -2,4'- et -3,4'- et les dimethyl-2,4'- et -3,4'-iodo-2- et -3-biphenyles

Photochemistry of diaryliodonium salts

Photolyse photosensibilisee du compose ci-dessus. Obtention de sulfures de diphenyle et de biphenylyle phenyle

Triphenylsulfonium salt photochemistry. New evidence for triplet excited state reactions

The direct and triplet-sensitized photochemistry of diphenylchloronium, diphenylbromonium, bis(4-methylphenyl) chloronium, and bis(4-methylphenyl) bromonium salts was studied. Direct photolysis of the diarylhalonium salts gave haloarene 2-, 3-, and 4-halobiaryls, and acetanilide, predominantly from a heterolytic cleavage mechanism via the aryl cation-haloarene pair, via in-cage recombination and cage-escape reactions. However, triplet-sensitized photolysis gave haloarene, 2-, 3-, and 4-halobiaryl, and reduced arene mainly from homolytic cleavage to the arene radical-haloarene radical cation pair, which also gave in-cage recombination and cage-escape products. There is evidence for singlet-triplet interconversion of the excited states by spin-orbit coupling and interconversion of the singlet-triplet radical pairs by spin-spin coupling. The effect of halogen and arene substituent on these interconversions is discussed

Comparison of the photochemistry of diarylchloronium, diarylbromonium, and diaryliodonium salts

Diphenyliodonium halides exist as tight ion pairs in acetonitrile, and photolysis gives almost exclusively iodobenzene by a homolytic cleavage reaction from a charge transfer excited state, whereas in aqueous acetonitrile the ion pairs are solvent separated and photolysis gives substantial amounts of 2-, 3-, and 4-iodobiphenyls, in addition to iodobenzene, by an initial heterolytic cleavage

Nigel P. Hacker

Papers

Photochemistry of triarylsulfonium salts

Photochemistry of diaryliodonium salts

Triphenylsulfonium salt photochemistry. New evidence for triplet excited state reactions

Comparison of the photochemistry of diarylchloronium, diarylbromonium, and diaryliodonium salts

The photochemistry of diphenyliodonium halides: evidence for reactions from solvent-separated and tight ion pairs