Carbazole structures are of high interest in photopolymerization due to their enhanced light absorption properties in the near-UV or even visible ranges. Therefore, type I photoinitiators combining ...the carbazole chromophore to the well-established phosphine-oxides were proposed and studied in this article. The aim of this article was to propose type I photoinitiators that can be more reactive than benchmark phosphine oxides, which are among the more reactive type I photoinitiators for a UV or near-UV light emitting diodes (LED) irradiation. Two molecules were synthesized and their UV-visible light absorption properties as well as the quantum yields of photolysis and photopolymerization performances were measured. Remarkably, the associated absorption was enhanced in the 350-410 nm range compared to benchmark phosphine oxides, and one compound was found to be more reactive in photopolymerization than the commercial photoinitiator TPO-L for an irradiation at 395 nm.
Novel naphthalimide derivatives (or naphthalic anhydride derivatives) have been prepared and combined with an iodonium salt, N-vinylcarbazole, amines or 2,4,6-tris(trichloromethyl)-1,3,5-triazine to ...produce radicals and cations upon exposure to low intensity blue lights (e.g., a household blue LED bulb). The photochemical mechanisms are studied by electron spin resonance spin trapping, fluorescence, cyclic voltammetry, laser flash photolysis, and steady state photolysis techniques. The naphthalimide derivatives (ND4) or the naphthalic anhydride derivative (ND10) based photoinitiating systems are particularly efficient for cationic, radical and thiol–ene photopolymerizations; the synthesis of interpenetrated polymer networks IPNs can also be easily carried out. Compared to camphorquinone/amine or camphorquinone/iodonium salt, the new proposed combinations appear as highly versatile and high performance visible light photoinitiating systems. Some of these photoinitiating systems can also be used for UV LED irradiations (e.g., 365, 385, or 395 nm).
Four N -2-(dimethylamino)ethyl-1,8-naphthalimide derivatives (ANNs) with different substituents (bromo group, primary amine, secondary amine, and tertiary amine) in the naphthalimide skeleton have ...been synthesized and can be used as one-component free radical photoinitiators or incorporated into multi-component photoinitiating systems for free radical or cationic photopolymerization under the irradiation of various LEDs. ANN2 (with secondary amine substituent) or ANN3 (with tertiary amine substituent) alone is capable of initiating the free radical polymerization of acrylates under a LED at 405 nm while ANN0 (with bromo substituent) or ANN1 (with primary amine substituent) does not work. When combined with various additives ( e.g. iodonium salt, N -vinylcarbazole, chloro triazine, or tertiary amine), most of the ANN1–3 based multi-component photoinitiating systems are efficient in free radical photopolymerization at 385 nm, 405 nm, 455 nm, 470 nm and even under a low-intensity polychromatic visible light (from a halogen lamp) with the final conversions being higher than 60% (even more efficient than commercial photoinitiators bisacylphosphine oxide and camphorquinone). In addition, ANN1–3 based photoinitiating systems also exhibit a high efficiency for cationic photopolymerization of epoxides upon diverse LEDs. The ANN2 based photoinitiating system can also be used for the synthesis of interpenetrated polymer networks and adapted for 3D printing. The photochemical mechanisms of the ANN based systems have been comprehensively investigated and discussed in detail.
In this paper, nine organic compounds based on the coumarin scaffold and different substituents were synthesized and used as high-performance photoinitiators for free radical photopolymerization ...(FRP) of meth(acrylate) functions under visible light irradiation using LED at 405 nm. In fact, these compounds showed a very high initiation capacity and very good polymerization profiles (both high rate of polymerization (Rp) and final conversion (FC)) using two and three-component photoinitiating systems based on coum/iodonium salt (0.1%/1%
/
) and coum/iodonium salt/amine (0.1%/1%/1%
/
/
), respectively. To demonstrate the efficiency of the initiation of photopolymerization, several techniques were used to study the photophysical and photochemical properties of coumarins, such as: UV-visible absorption spectroscopy, steady-state photolysis, real-time FTIR, and cyclic voltammetry. On the other hand, these compounds were also tested in direct laser write experiments (3D printing). The synthesis of photocomposites based on glass fiber or carbon fiber using an LED conveyor at 385 nm (0.7 W/cm
) was also examined.
Different polyaromatic structures (truxene derivatives and tris(aza)pentacene) are presented as new metal-free organic photocatalysts (OPC) to promote free radical polymerization FRP and ring-opening ...polymerization (ROP) under halogen lamp, household LED bulb, and laser diode (405 nm). These OPCs exhibit interesting light absorption properties and lead, through an oxidative catalytic cycle, to the formation of radicals and ions that can initiate both free radical polymerization FRP and ring-opening polymerization ROP. Interestingly, excellent polymerization profiles are obtained even upon visible light exposure. Using these very soft irradiation conditions, acrylate/epoxide blends are also easily polymerized under air and lead to the formation of interpenetrated polymer networks IPN exhibiting no phase separation.
Anthraquinone derivatives in combination with an iodonium salt (and optionally N-vinylcarbazole) have been used as photoinitiating systems. One of them (Oil Blue N) that is particularly efficient for ...cationic, IPN, and thiol–ene polymerization upon red lights (laser diode at 635 nm or household red LED bulb at 630 nm) belongs to the very few systems available at this long wavelength in such experimental conditions (low light intensity in the 10–100 mW/cm2 range). Their abilities to initiate the cationic photopolymerization of epoxides or vinyl ethers under very soft halogen lamp irradiation have been also investigated. The photochemical mechanisms are studied by steady state photolysis, fluorescence, cyclic voltammetry, and electron spin resonance spin trapping techniques.
New organic photocatalysts derived from pyrene, anthracene, naphthacene, and pentacene are presented here for the formation of free radicals through a photoredox catalysis. These OPCs can work ...according to an oxidative cycle in a three component system in combination with diphenyl iodonium salt and a silane or in a reductive cycle in combination with amine and alkyl halide. This OPC behavior is highlighted through an investigation of the associated excited state and redox properties. The free radicals generated are characterized by ESR or photolysis experiments. Upon household LED bulb or Xe lamp exposure, the oxidative three-component system is able to promote the ring-opening polymerization ROP of an epoxide whereas the reductive three-component system is very efficient to initiate the free radical photopolymerization FRP of an acrylate. This ability of OPCs to initiate different polymerization reactions (ROP and FRP) is clearly an outstanding property.
Three novel photoinitiators, namely (2,2′-bithiophen-5-yl)(4-( N , N ′-dimethylaminophenyl)ketone, 5,10-dimethoxybenzojfluoranthene and ...6,6′-(((1E,1′E)-(2,5-bis(octyloxy)-1,4-phenylene)bis(ethene-2,1-diyl))bis(4,1-phenylene))bis(1,3,5-triazine-2,4-diamine) applicable to different near UV or visible LEDs (385 nm, 395 nm, 405 nm or cold white LED) have been developed. When incorporated into multicomponent photoinitiating systems PISs (in the presence of iodonium salt (and optionally N-vinyl carbazole) or amine/alkyl halide couples), they exhibit quite excellent photoinitiating abilities for the cationic polymerization CP of epoxides or the free radical polymerization FRP of methacrylates under air. Compared to the corresponding camphorquinone-based systems, the newly developed photoinitiating systems display noticeably higher polymerization efficiencies under air (epoxide conversions = 31–55% vs ∼0%, halogen lamp exposure; methacrylate conversion = 56–66% vs 0–8%, LED irradiation). These systems are very interesting to overcome the oxygen inhibition. The photochemical mechanisms have been studied by steady state photolysis, electron spin resonance spin trapping, fluorescence, cyclic voltammetry, and laser flash photolysis techniques.
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.
Ascorbic acid is widely used in the food industry as a source of vitamin C or as antioxidant. However, it degrades quickly in beverages at acidic pH and can accelerate the degradation of ...anthocyanins, natural dyes used in beverages, leading to a loss of color. In this work, we investigated the possibility to replace ascorbic acid by ascorbic acid derivatives to prevent its degradation effect on anthocyanins from natural extracts (black carrot, grape juice, and purple sweet potato). For this, the thermal and photolytic stabilities under air and under N2 of ascorbic acid (as reference) and of some ascorbic acid derivatives (3-O-ethyl-l-ascorbic acid, 2-O-α-d-glucopyranosyl-l-ascorbic acid, l-ascorbic acid 2-phosphate sesquimagnesium salt hydrate, l-ascorbyl 2,6-dibutyrate, glyceryl ascorbate, (+)-5,6-O-isopropylidene-l-ascorbic acid), soluble in aqueous model beverages, were studied alone and in the presence of anthocyanins from the natural extracts in citrate buffer at pH 3. The stability was followed by UV–visible spectrometry. To extend the investigation, some properties of the ascorbic acid derivatives (pK a, oxidation potential, bond dissociation energy, ionization potential) were also determined. Moreover, the addition of chlorogenic acid was examined to further stabilize the mixture of anthocyanins with 2-O-α-d-glucopyranosyl-l-ascorbic acid, a promising ascorbic acid derivative.
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