Tetraacylgermanes: Highly Efficient Photoinitiators for Visible‐Light‐Induced Free‐Radical Polymerization

In this contribution a convenient synthetic method to obtain tetraacylgermanes Ge[C(O)R]₄ (R=mesityl ( 1 a ), phenyl ( 1 b )), a previously unknown class of highly efficient Ge‐based photoinitiators, is described. Tetraacylgermanes are easily accessible via a one‐pot synthetic protocol in >85 % yield, as confirmed by NMR spectroscopy, mass spectrometry, and X‐ray crystallography. The efficiency of 1 a , b as photoinitiators is demonstrated in photobleaching (UV/Vis), time‐resolved EPR (CIDEP), and NMR/CIDNP investigations as well as by photo‐DSC studies. Remarkably, the tetraacylgermanes exceed the performance of currently known long‐wavelength visible‐light photoinitiators for free‐radical polymerization     

Photophysical Investigations on Photoinitiators with Covalently Linked Thioxanthone Sensitizer Moieties

The photophysical properties of three photoinitiators with a covalently linked thioxanthone sensitizer unit absorbing up to 410 nm were investigated by laser‐flash photolysis and CIDNP spectroscopy. These complementary techniques revealed two competing reaction pathways of the molecular dyads 1 – 3 : i) triplet‐energy transfer from the sensitizer to the morpholine moiety followed by α‐cleavage to yield a radical pair, which initiates radical polymerization, and ii) bimolecular electron transfer from the morpholine to the thioxanthone subunit followed by proton transfer. The relative efficiency of these routes is determined by the triplet energy of the photoinitiator moiety relative to that of the sensitizer.     

Light‐Harvesting Organic Photoinitiators of Polymerization

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.     

Remarkable Mechanism of the Reaction between Mixed Phosphonium-Iodonium Ylides and Acetylenes

Reactions of mixed phosphonium-iodonium ylides with nitriles and acetylenes allow for the synthesis of not easily accessible and novel heterocyclic compounds in a simple, one-pot, metal-free system. The results of the mechanistic investigation of the reaction of the phosphonium-iodonium ylides with acetylenes by means of spectrophotometry, EPR and NMR spectroscopy are discussed in this review. This investigation allows to account for unusual regularities of these reactions: induction time, acid catalysis, chemically induced dynamic nuclear polarization effect (CIDNP) observed in several systems, and others. The radical character of the initiation of the reaction as a result of acid catalysis of the ylides decomposition on radicals and the participation of radical intermediates in the formation of all target products have been unambiguously established. The mechanism of generation of radical pairs in CIDNP was suggested, and the role of microheterogeniety of the ylide solutions in methylene chloride was substantiated. On the basis of the study of the reaction mechanism, the conditions for the increase in the yields of new heterocyclic compounds can be optimized.     

Organic dye-based photoinitiating systems for visible-light-induced photopolymerization

Even though many organic dyes have been reported as photoinitiators/photosensitizers for free radical polymerization in the literature, the design and development of novel photoinitiating systems based on organic dyes adaptable for visible light irradiation, for example, 405 nm LED and sunlight still remains challenging. Recently, major achievements in the development of high-performance photoinitiating systems based on organic dyes as light-harvesting compounds and their uses as photoinitiators for photopolymerization under visible-light irradiation have clearly emerged, giving rise to abundant literature. In this review, an overview of the recently synthesized chromophores belonging to various families of organic dyes and used as photoinitiators of polymerization during the 2018–2021 period are presented and classified. Recent works have resulted in the development of new chromophores exhibiting remarkable visible light absorption properties and excellent photoinitiation abilities upon irradiation with LEDs and/or sunlight in free radical photopolymerization processes. These developments notably indicate that sunlight has the advantages of being a cheap, unlimited, broad emission spectrum, and energy-saving light source capable to be an efficient substitute to artificial light sources. The newly developed dye-based photoinitiating systems designed to initiate visible-light-induced photopolymerization processes are likely to expand the scope of application of photopolymerization in modern sciences and technologies.     

Synthesis and photoactivity of novel 5‐arylthianthrenium salt cationic photoinitiators

5‐Arylthianthrenium salts are a class of efficient triarylsulfonium salt photoinitiators for cationic polymerization. These compounds were prepared by a simple, straightforward, versatile, and high yield route. The new photoinitiators were characterized by standard analytical and spectroscopic techniques, and their activity as cationic photoinitiators was compared with related triarylsulfonium salts of similar structures using Fourier transform real‐time infrared spectroscopy. Through the use of electron‐transfer photosensitizers, the response of these photoinitiators can be readily spectrally broadened into the long‐wavelength UV–visible regions of the spectrum. The results obtained suggest that 5‐arylthianthrenium salts are potential replacements for now available triarysulfonium salt photoinitiators in many applications. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3465–3480, 2002     

Photoinitiating Characteristics of Benzophenone Derivatives as Type II Macromolecular Photoinitiators Used for UV Curable Resins

Dodecyl-benzophenone(DBP) and hexadecoxyl-benzophenone(HDBP) as type II photoinitiators used for radical photopolymerization systems were synthesized by Friedel-Crafts reaction, and characterized by 1H NMR and FTIR spectroscopy. The UV-Vis absorption spectra of DBP and HDBP, propitious to photopolymerization under a commercial mercury UV bulb are centered at 345 and 335 nm, respectively. HDBP has higher extinction coefficient than DBP, but lower photoinitiating efficiency. Their photoinitiating performances...     

Synthesis of Some Novel Pyrazole‐Substituted 9‐Anilinoacridine Derivatives and Evaluation for their Antioxidant and Cytotoxic Activities

This article focuses on the synthesis of new series of pyrazole‐substituted 9‐anilinoacridine derivatives 5a – m and 6a – l . The compounds were confirmed by physical and analytical data. The synthesized compounds when screened for in vitro antioxidant activity showed promising activity for many compounds. The selected compounds were screened for cytotoxic activity showed promising inhibition of HEp‐2 cell line for the compounds 6c , 6e , and 6f .     

Keto-coumarin scaffold for photoinitiators for 3D printing and photocomposites

The purposes of this paper are moving toward (a) the development of a new series of photoinitiators (PIs) which are based on the keto-coumarin (KC) core, (b) the introduction of light-emitting diodes (LEDs) as inexpensive and safe sources of irradiation, (c) the study of the photochemical mechanisms through which the new PIs react using different techniques such as Fourier transform infrared, UV–visible or fluorescence spectroscopy, and so on, (d) the use of such compounds (presenting good reactivity and excellent photopolymerization initiating abilities) for two specific and high added value applications: 3D printing (@405 nm) and preparation of thick glass fiber photocomposites with excellent depth of cure, and finally (e) the comparison of the performance of these KC derivatives versus other synthesized coumarin derivatives. In this study, six well-designed KC derivatives ( KC-C , KC-D , KC-E , KC-F , KC-G , and KC-H ) are examined as high-performance visible-light PIs for the cationic polymerization of epoxides as well as the free-radical polymerization of acrylates upon irradiation with LED@405 nm. Excellent polymerization rates are obtained using two different approaches: a photo-oxidation process in combination with an iodonium (Iod) salt and a photo-reduction process when associated with an amine (N-phenylglycine or ethyl 4-(dimethylamino)benzoate). High final reactive conversions were obtained. A full picture of the involved photochemical mechanisms is provided.     

N-[5-(1-邻(对)氯苯氧乙基)-1,3,4-噻二唑-2-基]-N'-芳酰基硫脲的合成与生物活性

为了寻找高活性的杂环农药,通过2-氨基-5-(1-邻氯苯氧乙基)-1,3,4-噻二唑和2-氨基-5-(1-对氯苯氧乙基)-1,3,4-噻二唑与芳酰基异硫氰酸酯反应,合成了26种新的芳酰基硫脲.采用核磁共振氢谱、红外光谱及元素分析确证了它们的结构.初步的生物活性测定试验表明,部分目标化合物表现出良好的植物生长调节活性,其中3c,3d,3e,4b和4c具有优良的生长素活性.     

One‐component thioxanthone‐based polymeric photoinitiators

The photochemical and photophysical properties of new polymeric photoinitiators (PPIs) containing pendant thioxanthone (TX) and amine moieties are studied. The PPIs are synthesized by copolymerization of tert‐butyl 2‐((9‐oxo‐9H‐thioxanthen‐2‐yloxy)methyl)acrylate (TX1) with N,N‐dimethylaminoethyl methacrylate (DMAEM) at two different ratios using free radical polymerization. UV–vis spectra indicate that PPIs possess similar absorption characteristics to TX1 in the violet range (～400 nm; absorption red‐shift 20 nm). The photochemical mechanisms are studied by electron spin resonance (ESR), steady state photolysis, laser flash photolysis, and cyclic voltammetry. ESR studies indicate formation of two different aminoalkyl radicals on the hydrogen donor amine. The triplet state of the PPIs is short‐lived compared to isopropyl thioxanthone and TX1, due to the built‐in amine functionality. Photopolymerization of trimethylolpropane triacrylate (TMPTA) initiated by these photoinitiators under LED exposure at 385 and 405 nm using real‐time FTIR spectroscopy shows that they exhibit higher efficiency than TX/N‐methyldiethanolamine (MDEA) and TX1/MDEA systems with the advantage of a much higher molecular weight that can be very helpful to overcome migration issues. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3370–3378     

A facile one‐pot synthesis of novel substituted 1,2,3,4‐tetrahydropyrimidine,part 2: Synthesis of 1‐(aralkyl/aryl)‐3‐(alkyl/aralkyl/aryl)‐5‐aroyl‐1,2,3,4‐tetrahydropyrimidines

1‐(Aralkyl/aryl)‐3‐(alkyyaralkyl)‐5‐aroyl‐1,2,3,4‐tetrahydropyrimidines ( 2a‐c ) have been synthesized by dethiomethylation of 5‐aroyl‐6‐methylthio‐1,2,3,4‐tetrahydropyrimidines ( 1a‐c ). An alternative one‐pot synthetic strategy has been developed for the title compounds 2a‐t by the reaction of enaminones 3 with pri mary amine and formaldehyde in refluxing methanol in good yields.     

N-[5-(1-邻氯苯氧乙基)-1,3,4-噻二唑-2-基]-N′-芳酰基脲的合成及其生物活性

通过2-氨基-5-(1邻-氯苯氧乙基)-1,3,4噻-二唑与芳酰基异氰酸酯反应,合成了13种新的芳酰基脲。采用红外光谱,核磁共振氢谱和元素分析测试技术确证了结构。初步的生物活性测定试验表明,目标化合物具有良好的生长素活性,其中化合物2c、2d和2h的促进率分别为30.1%、32.5%和29.9%。     

N-[5-(4-吡啶基)-1,3,4-噻二唑-2-基]-N'-芳酰基脲的合成与生物活性

为了寻找高活性的含杂环的新农药, 通过2-氨基-5-(4-吡啶基)-1,3,4-噻二唑与芳酰基异氰酸酯反应, 合成了17种新的芳酰基脲, 采用红外光谱、核磁共振氢谱与元素分析证明了其结构. 初步的活性试验表明, 部分目标化合物具有良好的植物生长调节活性, 其中2c, 2e, 2f, 2i和2k具有较好的细胞分裂素活性.     

Aza‐BODIPY Derivatives: Enhanced Quantum Yields of Triplet Excited States and the Generation of Singlet Oxygen and their Role as Facile Sustainable Photooxygenation Catalysts

A new series of aza‐BODIPY derivatives ( 4 a – 4 c , 5 a , c , and 6 b , c ) were synthesized and their excited‐state properties, such as their triplet excited state and the yield of singlet‐oxygen generation, were tuned by substituting with heavy atoms, such as bromine and iodine. The effect of substitution has been studied in detail by varying the position of halogenation. The core‐substituted dyes showed high yields of the triplet excited state and high efficiencies of singlet‐oxygen generation when compared to the peripheral‐substituted systems. The dye 6 c , which was substituted with six iodine atoms on the core and peripheral phenyl ring, showed the highest quantum yields of the triplet excited state (Φ_T=0.86) and of the efficiency of singlet‐oxygen generation (Φ_Δ=0.80). Interestingly, these dyes were highly efficient as photooxygenation catalysts under artificial light, as well as under normal sunlight conditions. The uniqueness of these aza‐BODIPY systems is that they are stable under irradiation conditions, possess strong red‐light absorption (620–680 nm), exhibit high yields of singlet‐oxygen generation, and act as efficient and sustainable catalysts for photooxygenation reactions.     

Synthesis, crystal structures, and photophysical properties of triphenylamine-based multicyano derivatives

A new series of intramolecular charge transfer (ICT) molecules were synthesized by attaching various strong electron-withdrawing groups to a triphenylamine backbone. Relationships between chemical structures and optoelectronic properties of these compounds were investigated with X-ray diffraction, cyclic voltammetry, absorption spectroscopy, and density functional theory calculations. It is shown that the compounds exhibit intensive ICT interactions leading to substantial extension of their absorption spectral response, which may be potentially used for efficient solar cells.     

CIDNP studies of macromolecular systems. I. Photolysis of poly(methyl isopropenyl ketone) and its model compounds in solution

The photoreactions of poly(methyl isopropenyl ketone) (PMIK) and two low-molecular-weight model compounds have been investigated in solution with proton NMR spectroscopy. Chemically induced dynamic nuclear polarization (CIDNP) has been observed in all three systems, but the CIDNP intensities have been found to depend on the chain lengths of the reaction products: long-chain products fail to show CIDNP at room temperature, whereas simultaneously formed small fragments exhibit nuclear spin polarization. The CIDNP originates from the Norrish type I decomposition of the ketones, which for the polymer occurs from the triplet state in all solvents. In the model compounds this cleavage can occur from the triplet or singlet state. The main photoreaction of PMIK, namely, scission of the polymer backbone, does not give rise to CIDNP. The failure of long-chain products to display CIDNP is attributed in part to a relaxation phenomenon: the short nuclear spin relaxation times of the long-chain product molecules destroy the CIDNP before it can be detected. In high-temperature studies above 150°C, however, in which the relaxation times are longer, CIDNP has been detected in long-chain molecules as well.     

Synthesis and study of iodonium borate salts as photoinitiators

Iodonium butyltriphenylborate salts (A I⁺ Ar′Ph₃B⁻ R), (Bu) were found to be more efficient than iodonium tetraphenylborate salts (RPh) when used as photoinitiators for the polymerization of acrylates. Relative photodecomposition rates were also different. It was found from a study of the photoreaction of iodonium borate salts with a model monomer, methyl methacrylate, that iodonium butyltriphenylborate salts simultaneously produce a butyl radical from the borate anion and an aryl radical from the iodonium cation upon irradiation. Both radicals initiate polymerization. Iodonium tetraphenylborate salts were found to release an aryl radical, but only from the iodonium cation. Iodonium borate salts exhibit strong absorption below 300 nm with a tail absorption above 400 nm. Thus, iodonium butyltriphenyl borate salts are efficient photoinitiators even when used with visible light. When a photosensitizer such as 5,7-diiodo-3-butoxy-6-fluorone is employed, iodonium butyltriphenylborate salts are rendered much more efficient for visible light photopolymerization. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1667–1677, 1998     

1－芳酰基－4－芳基氨基脲类化合物的合成及表征

利用N－取代三氯乙酰胺与芳基酰肼反应，合成了6个新的1－芳酰基－4－芳基 氨基脲类化合物，其结构经IR，^1H NMR和元素分析证实。初步生物活性测试表明 ，具有一定的除草活性。     

Low‐Band Gap Polymeric Cyanine Dyes Absorbing in the NIR Region

Two new, fully conjugated polymeric cyanine dyes based on trimethine and heptamethine moieties have been synthesized. Both polymers were characterized by gel permeation chromatography, UV‐vis and IR spectroscopy, elementary analysis and cyclic voltammetry. The structure of one material could be confirmed with NMR spectroscopy. Upon head‐to‐tail coupling of the dye moieties distinct bathochromic shifts up to 159 nm were observed for the polymers which absorb solely in the near infrared (NIR) region with maxima up to 1 002 nm and very high molar absorption coefficients. This highly efficient absorption in the NIR spectral domain combined with the strong electron accepting properties makes these dyes interesting candidates for many optical applications; investigations on photovoltaic devices based on polymeric cyanine dye/C₆₀ heterojunctions identify one of these possibilities.