Recent advances on carbazole-based oxime esters as photoinitiators of polymerization

Novel Low-Cytotoxic and Highly Efficient Type I Photoinitiators for Visible LED-/Sunlight-Induced Photopolymerization and High-Precision 3D Printing

The development of photoinitiators (PIs) combining high initiation ability, low-toxicity, and availability for high-precision 3D printing is a key challenge and an urgent problem to be solved nowadays in photopolymerization. In this study, carbazole chalcone glyoxylate oxime ester derivatives (denoted as Cs, C1-C5) containing both glyoxylate and oxime ester moieties with good light absorption properties in the visible range have been designed as type I PIs for the free radical photopolymerization (FRP) of trimethylolpropane triacrylate (TMPTA) and ethoxylated trimethylolpropane triacrylate (ETPTA) under 405 nm and 450 nm light-emitting diodes (LEDs) as well as sunlight irradiation. The reaction properties and mechanism of Cs are firstly predicted by molecular modeling/molecular design, which anticipate that C5 could exhibit the best photoinitiation ability, this structure being more prone to decarboxylation. Subsequent experimental results clearly show that the photoinitiation ability of C5 outperforms that of the benchmark commercial PIs (methyl benzoylformate (MBF), diphenyl (2,4,6-trimethylbenzoyl) phosphine oxide (TPO)), and phenylbis (2,4,6-trimethylbenzoyl)-phosphine oxide (BAPO) under the same conditions. Compared to TPO, the photoinitiation ability of C5 improved by 40 %, 132 %, and 47 % exposed to LED@405 nm, LED@450 nm, and sunlight. In addition, C5 is successfully applied to 3D printing for the manufacture of large-scale and high-resolution object. The photochemical mechanism of C5 is systematically and comprehensively analyzed using a combination of steady state photolysis, decarboxylation reaction, fluorescence experiments, and electron spin resonance-spin trapping (ESR-ST) technology. It is found that both glyoxylate and oxime ester in C5 are highly active and capable of undergoing decarboxylation reactions to produce CO2 and free radicals, which is consistent with the results predicted by molecular modeling. Furthermore, the low-toxicity of C5 is evidenced by cytotoxicity assays. The comprehensive molecular modeling and experimental approach adopted in this research has led to the development of novel PIs that are highly efficient and low-toxic, and can be used for high-precision 3D printing, which offers broad application prospects in the fields of environmental sustainability, visible light curing, and biomedical science.

Novel High-Performance Glyoxylate Derivative-Based Photoinitiators for Free Radical Photopolymerization and 3D Printing with Visible LED

Investigations concerning the glyoxylate moiety as a photocleavable functional group for visible light photoinitiators, particularly in the initiation of free radical photopolymerization remain limited. This study introduces nine innovative carbazole-based ethyl glyoxylate derivatives (CEGs), which are synthesized and found to exhibit excellent photoinitiation abilities as monocomponent photoinitiating systems. Notably, these structures demonstrate robust absorption in the near-UV/visible range, surpassing the commercial photoinitiators. Moreover, the newly developed glyoxylate derivatives show higher acrylate function conversions compared to a benchmark photoinitiator (MBF) in free radical photopolymerization. Elucidation of the photoinitiation mechanism of CEGs is achieved through a comprehensive analysis involving the decarboxylation reaction and electron spin resonance spin trapping. Furthermore, their practical utility is confirmed during direct laser writing and 3D printing processes, enabling the successful fabrication of 3D printed objects. This study introduces pioneering concepts and effective strategies in the molecular design of novel photoinitiators, showcasing their potential for highly advantageous applications in 3D printing.

5,12-Dihydroindolo[3,2-a]Carbazole Derivatives-Based Water Soluble Photoinitiators for 3D Antibacterial Hydrogels Preparation

Indolo[3,2-a]carbazole alkaloids have drawn a growing interest in recent years owing to their potential electrical and optical properties. With 5,12-dihydroindolo[3,2-a]carbazole serving as the scaffold, two novel carbazole derivatives are synthesized in this study. Both compounds are extremely soluble in water, with solubility surpassing 7% in weight. Intriguingly, the introduction of aromatic substituents contributed to drastically reduce the π-stacking ability of carbazole derivatives, while the presence of the sulfonic acid groups enables the resulting carbazoles remarkably soluble in water, allowing them to be used as especially efficient water-soluble PIs in conjunction with co-initiators, i.e., triethanolamine and the iodonium salt, respectively, employed as electron donor and acceptor. Surprisingly, multi-component photoinitiating systems based on these synthesized carbazole derivatives could be used for the in situ preparation of hydrogels containing silver nanoparticles via laser write procedure with a light emitting diode (LED)@405 nm as light source, and the produced hydrogels display antibacterial activity against Escherichia coli.

Recent Advances in Monocomponent Visible Light Photoinitiating Systems Based on Sulfonium Salts

During the last decades, multicomponent photoinitiating systems have been the focus of intense research efforts, especially for the design of visible light photoinitiating systems. Although highly reactive three-component and even four-component photoinitiating systems have been designed, the complexity to elaborate such mixtures has incited researchers to design monocomponent Type II photoinitiators. Using this approach, the photosensitizer and the radical/cation generator can be combined within a unique molecule, greatly simplifying the elaboration of the photocurable resins. In this field, sulfonium salts are remarkable photoinitiators but these structures lack absorption in the visible range. Over the years, various structural modifications have been carried out in order to redshift their absorptions in the visible region. In this work, an overview of the different sulfonium salts activable under visible light and reported to date is proposed.

Design, synthesis, molecular docking and biological evaluation of new carbazole derivatives as anticancer, and antioxidant agents

BACKGROUND

The carbazole skeleton is an important structural motif occurring naturally or synthesized chemically and has antihistaminic, antioxidant, antitumor, antimicrobial, and anti-inflammatory activities.

OBJECTIVES

This study aimed to design and synthesize a novel series of carbazole derivatives and evaluate their antiproliferative and antioxidant activities.

METHODS

The synthesized compounds were characterized utilizing HRMS, ¹H-, and ¹³C_APT-NMR, and assessed for their anticancer, antifibrotic, and antioxidant effects utilizing reference biomedical procedures. In addition, the AutoDock Vina application was used to perform in-silico docking computations.

RESULTS

A series of carbazole derivatives were synthesized and characterized in the current study. Compounds 10 and 11 were found to have a stronger antiproliferative effect than compounds 2-5 against HepG2, HeLa, and MCF7 cancer cell lines with IC₅₀ values of 7.68, 10.09, and 6.44 µM, respectively. Moreover, compound 9 showed potent antiproliferative activity against HeLa cancer cell lines with an IC₅₀ value of 7.59 µM. However, except for compound 5, all of the synthesized compounds showed moderate antiproliferative activities against CaCo-2 with IC₅₀ values in the range of 43.7-187.23 µM. All of these values were compared with the positive control anticancer drug 5-Fluorouracil (5-FU). In addition, compound 9 showed the most potent anti-fibrotic compound, and the cellular viability of LX-2 was found 57.96% at 1 µM concentration in comparison with the positive control 5-FU. Moreover, 4 and 9 compounds showed potent antioxidant activities with IC₅₀ values of 1.05 ± 0.77 and 5.15 ± 1.01 µM, respectively.

CONCLUSION

Most of the synthesized carbazole derivatives showed promising antiproliferative, antioxidant, and antifibrotic biological effects, and further in-vivo investigations are needed to approve or disapprove these results.

Recent Advances on Furan-Based Visible Light Photoinitiators of Polymerization

Photopolymerization is an active research field enabling to polymerize in greener conditions than that performed with traditional thermal polymerization. At present, a great deal of effort is devoted to developing visible light photoinitiating systems. Indeed, the traditional UV photoinitiating systems are currently the focus of numerous safety concerns so alternatives to UV light are being actively researched. However, visible light photons are less energetic than UV photons so the reactivity of the photoinitiating systems should be improved to address this issue. In this field, furane constitutes an interesting candidate for the design of photocatalysts of polymerization due to its low cost and its easy chemical modification. In this review, an overview concerning the design of furane-based photoinitiators is provided. Comparisons with reference systems are also established to demonstrate evidence of the interest of these photoinitiators in innovative structures.

Naphthalene-Based Oxime Esters as Type I Photoinitiators for Free Radical Photopolymerization

In order to discuss the polymerization effect from the substituted position and methoxy group of Type I photinitiators, a series of naphthalene-based oxime esters was designed and synthesized. Compared to the 2-naphthalene-substituted compound, the UV absorption region of the 1-naphthalene-based compound was greatly improved. In addition, the methoxy substitution exhibited longer absorption characteristics than did the methoxy-free one. The photochemical reaction behavior of these novel compounds was also studied by photolysis, cyclic voltammetry (CV), and electron spin resonance (ESR) experiments. Finally, the initiation abilities of naphthalene-based oxime esters toward trimethylolpropane triacrylate (TMPTA) monomer were conducted through the photo-DSC instrument under UV and a 405@nm LED lamp. Remarkedly, the naphthalene-based oxime ester (NA-3) that contains 1-naphthalene with o-methoxy substituent showed the rather red-shifted absorption region with the highest final conversion efficiency under UV (46%) and 405@nm LED (41%) lamp irradiation.