Photoactive Monomer Research Articles

Impact of TiO2, ZnO, and Methylene Blue Doping on the Dielectric anisotropy of planar 8CB nematic liquid crystal

In this study, the impact on the dielectric properties of 8CB with the dispersion of TiO2, ZnO, and methylene blue (0% to 5%) is examined. Employing capacitance–voltage (C–V) measurements across frequencies ranging from 10 kHz to 2 MHz, we explore the combined effects of dispersed photoactive nanoparticles and mono/polymeric materials like MB. Our investigation provides novel insights into the nuanced variations induced by transition-metal oxide loaded 8CB, highlighting the role of their oxidation states, and elucidates the influence of larger photoactive monomers on 8CB’s dielectric polarizability. The study found that the dielectric anisotropy was strongly influenced by frequency and doping, changing sign at a critical frequency. Our work represents the first comparative analysis incorporating these oxides alongside photoactive materials like MB.

Synthesis and characterization of functional thermoresponsive photoactive copolymers and study of their thermal and photoluminescence properties

ABSTRACT Poly(N-isopropyl acrylamide-co-disperse yellow 7 methacrylate) (PNIPAM) copolymers were synthesized by radical polymerization of N-isopropyl acrylamide with disperse yellow 7 methacrylate using 2,2/-Azo-bis-isobutyronitrile (AIBN) as an initiator. N-isopropyl acrylamide is a thermoresponsive monomer, and disperse yellow 7 methacrylate is a photoactive monomer. The synthesized photoactive and thermoresponsive copolymers were characterized by FTIR, NMR, and UV-Vis spectrophotometer with a temperature variation. A proton NMR signal at 8.16 ppm is observed for aromatic protons surrounded by an azo (-N=N-) group. The peak that appeared at 4.0 ppm is due to the CH-CONH group. The amide group proton of CONH appeared at 8.16 ppm. The molecular weights of homopolymers (like PNIPAM and PDY7MA) and their copolymers (PNIPDY) were observed to be 104 and 103 Da, respectively. The optical band gaps for synthesized copolymers, PNIPDY-1B, PNIPDY-2B, and PNIPDY-3B, are 2.98 eV, 2.95 eV, and 2.91 eV, respectively. The multiple emission spectra were observed at 407 nm, 428 nm, and 460 nm for the excitation energy of 365 nm due to the n-π* and π-π* transitions of the azobenzene chromophore. Thermal properties were also studied using TGA analysis. Stimuli-responsive polymers are widely used in optoelectronics and photonics, such as optical switching, optical information storage devices, liquid crystal display technology, and diffractive optical elements.

Impact of Photoactive Monomer Location in Photoresponsive Block Copolymer/Ionic Liquid Solutions

By incorporating a photoactive moiety into a block polymer, the phase behavior can be controlled with light. Previous studies have looked at situating azobenzene, a common photoresponsive molecule, along the backbone of the polymer as a pendant group, and even as part of the solvent rather than as a comonomer. Here, we study the effect of the positioning of pendant azobenzene groups along the polymer backbone on the lower critical disorder–order transition of poly(methyl methacrylate)-block-poly(benzyl methacrylate) (PMMA-b-PBnMA, or MB) in the ionic liquid 1,3-dimethyl imidazolium bis(trifluoromethylsulfonyl)imide. Using small-angle X-ray scattering and ultraviolet (UV)-irradiated small-amplitude oscillatory shear rheology, the placement of azobenzene statistically along the benzyl methacrylate backbone (MBsA) is compared to locating it as a midblock between the PMMA and the PBnMA (MAB) or as an end block after the PBnMA (MBA). Two concentrations of polymer in the ionic solvent were studied, 35 and 50 wt %. At 35 wt %, MBsA microphase-separated at 60 °C, MBA at 100 °C, and followed by MAB at 120 °C, a trend that was repeated at 50 wt %. MBsA was the only polymer to order onto a lattice at 35 wt %, forming hexagonally close-packed spheres. Both MBsA and MBA formed hexagonally packed cylinders at 50 wt %. MBsA consistently ordered onto a lattice over the temperature range of interest, while MBA only did so at 50 wt %, and MAB remained disordered at both concentrations. MBsA was also the only sample of the three to successfully transition reversibly between order and disorder with light. Therefore, adjusting the location of the azobenzene units within the thermo- and photoresponsive polymer solution significantly changes the overall behavior of the solutions and the ability to control that behavior with light and temperature.

Amphiphilic di-cationic methylene blue for improving antibacterial photodynamic efficiency through high accumulation and low aggregation on bacterial cell surfaces.

The aggregation state of photosensitizers on the surface of bacterial cells is an important scientific problem for antibacterial photodynamic therapy (APDT). High accumulation and high photoactive state maintenance of photosensitizers are the prerequisite of high APDT efficiency. In this study, an amphiphilic di-cationic methylene blue photosensitizer (C12-MB) was synthesized through quaternization, and its structure, interface properties, photophysical properties and antibacterial photodynamic properties were studied. The results showed that C12-MB could reduce 4.27 log10 CFU and 4.8 log10 CFU for P. aeruginosa and S. aureus under irradiation of light at 660 nm, higher than the parent methylene blue. Through a spectroscopic study on photosensitizer adsorption over the bacterial surface, C12-MB can be accumulated with higher concentration, and the photo-active monomer content is 73% and 70% over P. aeruginosa and S. aureus, higher than those of methylene blue: 25% and 49%, respectively. The higher content of non-aggregated photo-active monomer could contribute to higher antibacterial photodynamic efficiency. For C12-MB adsorbed over bacterial surfaces, planar packing inhibition and electrostatic repulsion could contribute to lower C12-MB aggregation, which provides an useful reference for the structural design of high-efficiency photosensitizers.

UV‐curable inorganic precursors enable direct 3D printing of SiOC ceramics

Abstract3D ceramic parts are of great interest for various applications including aerospace, defense, electronics, photonics, and biomedical. Yet, additive manufacturing of ceramics is challenging due to their poor machinability. Herein, two approaches based on the chemical modification of silicon resins to obtain UV‐curable preceramic precursors of SiOC are described. The dual functionality of the synthesized resins acting both as preceramic precursor and as photopolymerizable entity under UV light is exploited. A set of characterization techniques has allowed the investigation of the mechanisms involved in the synthesis of the inorganic SiOC precursors according to the following approaches: (1) blend of the silicon resin with photoactive monomers and (2) synthesis of a single source UV‐curable preceramic silicon resin. A correlation between the nature of the precursor and the properties of the derived SiOC is analyzed. From a technological point of view, the materials can be fabricated as dense or crack‐free porous customized objects with low mass loss and optimal surface quality.

Microspheres from light—a sustainable materials platform

Driven by the demand for highly specialized polymeric materials via milder, safer, and sustainable processes, we herein introduce a powerful, purely light driven platform for microsphere synthesis – including facile synthesis by sunlight. Our light-induced step-growth precipitation polymerization produces monodisperse particles (0.4–2.4 μm) at ambient temperature without any initiator, surfactant, additive or heating, constituting an unconventional approach compared to the classically thermally driven synthesis of particles. The microspheres are formed via the Diels-Alder cycloaddition of a photoactive monomer (2-methylisophthaldialdehyde, MIA) and a suitable electron deficient dienophile (bismaleimide). The particles are stable in the dry state as well as in solution and their surface can be further functionalized to produce fluorescent particles or alter their hydrophilicity. The simplicity and versatility of our approach introduces a fresh opportunity for particle synthesis, opening access to a yet unknown material class.

A pH-Triggered Polymer Degradation or Drug Delivery System by Light-Mediated Cis/Trans Isomerization of o-Hydroxy Cinnamates.

A new methodology for the pH-triggered degradation of polymers or for the release of drugs under visible light irradiation based on the cyclization of ortho-hydroxy-cinnamates (oHC) to coumarins is described. The key oHC structural motif can be readily incorporated into the rational design of novel photocleavable polymers via click chemistry. This main-chain moiety undergoes a fast photocleavage when irradiated with 455nm light provided that a suitable base is added. A series of polyethylene glycol-alt-ortho-hydroxy cinnamate (polyethylene glycol (PEG)n -alt-oHC)-based polymers are synthesized and the time-dependent visible-light initiated cleavage of the photoactive monomer and polymer is investigated in solution by a variety of spectroscopic and chromatographic techniques. The photo-degradation behavior of the water-soluble poly(PEG2000 -alt-oHC) is investigated within a broad pH range (pH = 2.1-11.8), demonstrating fast degradation at pH 11.8, while the stability of the polymer is greatly enhanced at pH 2.1. Moreover, the neat polymer shows long-term stability under daylight conditions, thus allowing its storage without special precautions. In addition, two water-soluble PEG-based drug-carrier molecules (mPEG2000 -oHC-benzhydrol/phenol) are synthesized and used for drug delivery studies, monitoring the process by UV-vis spectroscopy in an ON/OFF intermittent manner.

Photofunctionalizable Hydrogel for Fabricating Volume Optical Diffractive Sensors

AbstractVolume amplitude gratings made of mesoporous hydrogels are beneficial for sensing, but are difficult to fabricate because they involve creating high aspect ratio features in soft materials. A novel photofunctionalizable hydrogel is reported and its suitability for fabricating grating sensors is demonstrated comprising of features with an aspect ratio of ≈3.2. To make a photofunctionalizable hydrogel with high optical quality that can be patterned using widely available light sources, a water‐soluble photoactive monomer and sensitizer are synthesized. A transmission amplitude grating is subsequently fabricated in a ≈100 µm thick photofunctionalizable hydrogel film by reaction of the free amines generated in the photoexposed regions with pH‐responsive fluorescein isothiocyanate. The volume hydrogel grating described herein is shown to be suitable for real‐time sensing of pH as an exemplar analyte. This work will have a significant impact on the fabrication of diffractive optical structures in thick films of hydrogels that are highly promising for biomolecular sensing in disease diagnosis and healthcare monitoring.

Additive manufacturing of photoactive polymers for visible light harvesting

In recent years, 3D printing has gained a great deal of attention in the energy field, with numerous reports demonstrating its application in fabrication of electrochemical devices. The near-complete freedom of design offered by 3D printing technologies make them very appealing, since complex 3D parts can be directly fabricated. However, its application in photochemistry and solar energy harvesting remains, so far, an uncharted territory. In this work, a photoactive monomer was incorporated into commercially available 3D printing resin, which was subsequently used to successfully fabricate 3D photosensitizing structures for singlet oxygen generation. Results indicate that the SLA fabricated small-scale (0.1 ml) photoactive continuous flow reactor shows activity in singlet oxygen synthesis reaction under visible light irradiation (420 nm).

Photoactive and metal-free polyamide-based polymers for water and wastewater treatment under visible light irradiation

A photoactive benzothiadiazole (BT) based monomer was developed and used in the synthesis of typical polyamide (PA) polymers. The monomer was incorporated in different percentages within the PA backbone of the polymers and their photosensitising ability was tested in different media and conditions. Photochemical experiments in a commercial flow reactor under aerobic conditions showed that the polymers had increased efficiency in singlet oxygen generation compared to the original photoactive monomer. When suspended in aqueous solutions, these materials demonstrated superior photostability towards long-term exposure to light and chemical stability in a wide-range of pH environments. The photoactive polymers were highly capable of degrading two well-known wastewater contaminants, bisphenol A (BPA) and cimetidine, as well as inactivating the waterborne parasite Cryptosporidium. Given the simplicity of the synthetic preparation of the polymers, the absence of metals and their photoactivity under visible light, herein we show that these materials are very promising for simultaneous decontamination and disinfection of water.

FRET Phenomenon in Photoreversible Dual-Color Fluorescent Polymeric Nanoparticles Based on Azocarbazole/Spiropyran Derivatives

Incorporation of chromophores into a polymer chain results in prominent photoreversibility and fatigue resistance, photostability over the long term, and restriction of the internal conversion (IC). Here, we report the copolymerization of two photoactive monomers with methyl methacrylate via emulsion polymerization in order to obtain photoswitchable dual-color fluorescent nanoparticles. For this purpose, azocarbazole ethyl acrylate (AzoCzEA) and spiropyran ethyl acrylate (SPEA) were synthesized and the fluorescence polymeric latex nanoparticles were prepared correspondingly. FT-IR and 1HNMR spectra were used to confirm the structure of novel fluorescent AzoCzEA. UV–vis studies of the obtained nanoparticles displayed the spectral features of both AzoCzEA and SPEA under stimuli-irradiation and inclusion of these chromophores into the polymer particles. DSC analysis revealed an increase in Tg of the prepared copolymer, indicating covalently incorporation of the photoactive monomers into the polymer chains. T...

Synthesis and photo-postmodification of zeolite L based polymer brushes

Zeolite L macroinitiators are used for controlled radical copolymerization of a photo-active monomer and subsequent spin trapping of nitroxides results in diversely functionalized particles.

Influence of polymer stabilization on the dielectric relaxations of an antiferroelectric liquid crystal

Dielectric spectroscopic investigations are reported on an antiferroelectric liquid crystal in its pristine form and when stabilized by a polymer network without and with application of a DC bias field. While the in-phase mode associated with the helix distortion is hardly affected, the high frequency mode connected with the antiphase fluctuations shows a large decrease with increasing concentration of the photoactive monomer used to generate the polymer stabilization. With the help of X-ray data, we rule out any inter-layer nanophase segregation of the polymer strands, and argue that this strong effect is due to the large elastic interaction between the liquid crystal molecules and the polymer strands. Employing expression from a Landau theory we extract several relevant parameters, including the viscosities associated with the different relaxation modes, the elastic constant, and importantly the antiferroelectric interaction, which exhibits a substantial decrease upon polymer stabilization.

Green proteorhodopsin reconstituted into nanoscale phospholipid bilayers (nanodiscs) as photoactive monomers.

Over 4000 putative proteorhodopsins (PRs) have been identified throughout the oceans and seas of the Earth. The first of these eubacterial rhodopsins was discovered in 2000 and has expanded the family of microbial proton pumps to all three domains of life. With photophysical properties similar to those of bacteriorhodopsin, an archaeal proton pump, PRs are also generating interest for their potential use in various photonic applications. We perform here the first reconstitution of the minimal photoactive PR structure into nanoscale phospholipid bilayers (nanodiscs) to better understand how protein-protein and protein-lipid interactions influence the photophysical properties of PR. Spectral (steady-state and time-resolved UV-visible spectroscopy) and physical (size-exclusion chromatography and electron microscopy) characterization of these complexes confirms the preparation of a photoactive PR monomer within nanodiscs. Specifically, when embedded within a nanodisc, monomeric PR exhibits a titratable pK(a) (6.5-7.1) and photocycle lifetime (∼100-200 ms) that are comparable to the detergent-solubilized protein. These ndPRs also produce a photoactive blue-shifted absorbance, centered at 377 or 416 nm, that indicates that protein-protein interactions from a PR oligomer are required for a fast photocycle. Moreover, we demonstrate how these model membrane systems allow modulation of the PR photocycle by variation of the discoidal diameter (i.e., 10 or 12 nm), bilayer thickness (i.e., 23 or 26.5 Å), and degree of saturation of the lipid acyl chain. Nanodiscs also offer a highly stable environment of relevance to potential device applications.

Dynamic monitoring of refractive index change through photoactive resins

Objectives The change in optical characteristics through the bulk of curing photopolymers is not fully understood. Photopolymerization processes are accompanied by photoinitiator absorption, density changes and volumetric shrinkage, which alter optical properties and affects curing efficiency through depth. Methods This investigation demonstrates the use of a novel low coherence interferometry technique for simultaneous measurement of optical (refractive index) and physical (shrinkage) properties throughout curing of photoactive monomers containing various concentrations of bisphenol-A-diglycidyl ether dimethacrylate and triethylene glycol dimethacrylate. Results Reliability of the interferometry technique was compared with an Abbé refractometer and showed a significant linear regression relationship ( p < 0.001; adjusted R 2 > 0.99) for both uncured and cured resins. The extent and rate of refractive index change and magnitude of shrinkage strain was dependent upon monomer formulation. Significance The development of this interferometry technique provides a powerful non-invasive tool that will be useful for improving light transmission through photoactive resins and filled resin composites by precise control of optical properties through material bulk.

Consistent determinations for the diffusion and reaction rate coefficients of photoactive monomers under holographic exposure

Consistent determinations for the diffusion and reaction rate coefficients of photoactive monomers under holographic exposure

Copolymers Containing Phosphorescent Iridium(III) Complexes Obtained by Free and Controlled Radical Polymerization Techniques

AbstractA methacrylate‐functionalized phosphorescent Ir(III)‐complex has been synthesized, characterized, and applied as a monomer in radical copolymerizations. Together with methyl methacrylate, the complex has been copolymerized under free radical polymerization conditions. Aiming for host‐guest‐systems, applicable e.g. in organic light emitting devices (OLEDs), the complex was further copolymerized with a methacrylate‐functionalized carbazole derivative using the atom transfer radical polymerization technique. Applying gel permeation chromatography, in combination with a photodiode array detector, could clearly prove the formation of the copolymers. The optical properties of the photoactive monomers as well as the copolymers were investigated by absorption and emission spectroscopy (in solution). For the carbazole‐copolymer, the emission originates almost exclusively from the complex. This provides evidence of an efficient intrachain energy transfer, which makes the system an interesting candidate for potential OLED applications.magnified image

Direct photofabrication of focal-length-controlled microlens array using photoinduced migration mechanisms of photosensitive sol-gel hybrid materials

Photosensitive sol-gel hybrid (SGH) materials exhibited the peculiar photoinduced migration behavior of unreacted molecules from unexposed areas to exposed areas by selective UV exposure. Using the photoinduced migration mechanism of the photosensitive SGH materials, the microlens array (MLA) with a smooth surface was directly photofabricated, and the focal length was controlled by changing the photoinduced migration parameters. The higher photoactive monomer content and the thicker film creating a higher curvature produced a smaller focal length of the MLA. Thus, a simple fabrication and easy control of the focal length can be applicable to a fabrication of an efficient MLA.

Silica Monoliths Templated on L3 Liquid Crystal

Dimensionally stable, optically clear, highly porous (approximately 65% of the apparent volume), and high surface area (up to 1400 m(2)/g) silica monoliths were fabricated as thick disks (0.5 cm) by templating the isotropic liquid crystalline L(3) phase with silica through the hydrolysis and condensation of a silicon alkoxide and then removing the organic constituents by supercritical ethanol extraction. The L(3) liquid crystal is a stable phase formed by the cosurfactants cetylpyridinium chloride monohydrate and hexanol in HCl(aq) solvent. Extracted 0.5 cm thick disks exhibited a low ratio of scattered to transmitted visible light (1.5 x 10(-)(6) at 22 degrees from the surface normal). The degree of silica condensation in the monoliths was high, as determined by (29)Si NMR measurements of Q(3) and Q(4) peak intensities (0.53 and 0.47, respectively). As a result, the extracted and dried monoliths were mechanically robust and did not fracture when infiltrated by organic solvents. Photoactive liquid monomers were infiltrated into extracted silica monoliths and polymerized in situ, demonstrating the possible application of templated silica to optical storage technology.

Photoactive, liquid‐crystalline, hyperbranched benzylidene polyesters: Synthesis and characterization

AbstractA novel photoactive, liquid‐crystalline, hyperbranched benzylidene polyester (PAHBP) was synthesized from a dilute solution of an A2 photoactive monomer [bis(4‐hydroxybenzylidene)‐4‐phenyl cyclohexanone] and a B3 monomer (1,3,5‐benzene tricarboxylic acid chloride) by the solution polycondensation method in the presence of pyridine as a condensing agent. PAHBP was thoroughly characterized by Fourier transform infrared, 1H and 13C NMR, ultraviolet–visible spectrometry, and gel permeation chromatography. The inherent viscosity of the polymer was 0.35 dL/g in tetrahydrofuran. The degree of branching was 0.53, which confirmed the branched architecture of the polymer. Furthermore, thermogravimetric analysis, differential scanning calorimetry, and polarized optical microscopy were used to examine the thermal stability and thermotropic liquid‐crystalline properties of the hyperbranched polyester. The polymer exhibited a nematic mesophase over a wide range of temperatures. The photoreactivity of PAHBP was studied by photolysis under ultraviolet light. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 53–61, 2006