Azobenzene Dyes Research Articles

Experimental study on the dynamic mechanical response of a blue light-stimulated acrylate side chain liquid crystal elastomer.

This study demonstrates a breakdown analysis of the dynamics of a liquid crystal elastomer (LCE) including quality check, geometric measurement, thermal characterization, and comparison of heat- and light-induced contractions. A blue light-responsive acrylate side chain LCE with 1% azobenzene dye was characterized. From a classical viewpoint, photo-thermal contraction is considered a dominating effect, while direct photo-mechanical deformation can be neglected due to a low dye percentage. However, the findings of this research suggest that a low percentage of azobenzene dye does not necessarily lead to heat-dominating dynamics of LCE. This phenomenon has not yet been quantitatively studied before. The approach reported in this Letter can potentially be used to extract the data to improve the dynamics models of light-driven LCEs.

CIELAB Color Space as a Field for Tracking Color-Changing Chemical Reactions of Polymeric pH Indicators.

Two types of cross-linked polymeric dye films that exhibit reversible color changes in response to pH were prepared. Upon protonation, films with a nitrophenol dye moiety (NP) changed from yellow to colorless, whereas films with an azobenzene dye moiety (AB) changed from yellow to reddish-purple. The colored light transmitted through these films from a D65 white-light source was measured colorimetrically, and the transition of the chromaticity point in CIELAB upon protonation of the polymeric dyes was observed. At low dye concentrations ([NP] < 4.7 × 10-5 and [AB] < 2.7 × 10-5 mol L-1), linear loci of the chromaticity points were displayed for both polymeric dye films, indicating perceptual linearity. This linearity is caused by the avoidance of nonlinear perceptual phenomena such as the Abney effect and the Bezold-Brücke phenomenon. The perceptual linearity of space is a necessary condition for achieving stoichiometric linearity, which requires an additional linear relationship between the dye concentration and each component, a*, b*, and L*. A geometric equation that included the AB concentration and the protonation ratio of AB was used to successfully depict, on the basis of stoichiometric linearity, the protonation of the polymeric AB films three-dimensionally in the restricted area of CIELAB.

Combining UV-Vis and Resonance Raman Spectroscopy to Characterize Molecular Aggregation

In this work, we use UV-Vis and Raman spectroscopy to correlate the intensity of selected transitions to the onset of aggregation phenomena. Through TDDFT calculations, we rationalize the formation of H-aggregates and their influence on the observed changes in the UV-Vis spectra. A correlation between Raman intensity and the molar absorption coefficient is experimentally observed and theoretically rationalized. We develop this method by considering Disperse Orange 3 (DO3), a well-known push–pull azobenzene dye with strong optical absorption in the blue–green region of the visible spectrum, and the known tendency to form H-aggregates.

72‐3: High‐performance In‐cell Polarizer with a Multi‐layer Structure for Liquid Crystal Displays

This work demonstrates a high‐performance in‐cell polarizer adopting photo‐aligned azobenzene dyes. On the strength of the multilayered design, a simple fabrication process has been developed to assemble an in‐cell polarizer. We have achieved a broadband dichroic ratio after the long‐term stability test. Meanwhile, the cell with the proposed in‐cell polarizer can be driven regularly without a voltage boost, which renders excellent practicability in liquid crystal display technologies. The structure, fabrication process, and properties of the in‐cell polarizer in TN‐LCD are thoroughly discussed.

Supramolecular Complexation of Azobenzene Dyes by Cucurbit[7]uril.

This report describes cucurbit[7]uril (CB7) complexation of azobenzene dyes that have a 4-(N,N'-dimethylamino) or 4-amino substituent. Absorption and NMR data show that CB7 encapsulates the protonated form of the azobenzene and that the complexed dye exists as its azonium tautomer with a trans azo conformation and substantial quinoid resonance character. Because CB7 complexation stabilizes the dye conjugate acid, there is an upward shift in its pKa, and in one specific case, the pKa of the protonated azobenzene is increased from 3.09 to 4.47. Molecular modeling indicates that the CB7/azobenzene complex is stabilized by three major noncovalent factors: (i) ion-dipole interactions between the partially cationic 4-(N,N'-dimethylamino) or 4-amino group on the encapsulated protonated azobenzene and the electronegative carbonyl oxygens on CB7, (ii) inclusion of the upper aryl ring of the azobenzene within the hydrophobic CB7 cavity, and (iii) a hydrogen bond between the proton on the azo nitrogen and CB7 carbonyls. CB7 complexation enhances azobenzene stability and increases azobenzene hydrophilicity; thus, it is a promising way to improve azobenzene performance as a pigment or prodrug. In addition, the striking yellow/pink color change that accompanies CB7 complexation can be exploited to create azobenzene dye displacement assays with naked eye detection.

Optically Controlled Construction of Three-Dimensional Protein Arrays.

Protein crystallization is an important tool for structural biology and nanostructure preparation. Here, we report on kinetic pathway-dependent protein crystals that are controlled by light. Photo-responsive crystallites are obtained by complexing the model proteins with cationic azobenzene dyes. The crystalline state is readily switched to a dispersed phase under ultraviolet light and restored by subsequent visible-light illumination. The switching can be reversibly repeated for multiple cycles without noticeable structure deterioration. Importantly, the photo-treatment not only significantly increases the crystallinity, but creates crystallites at conditions where no ordered lattices are observed upon directly mixing the components. Further control over the azobenzene isomerization kinetics produces protein single crystals of up to ≈50 μm. This approach offers an intriguing method to fabricate metamaterials and study optically controlled crystallization.

Optically Controlled Construction of Three‐Dimensional Protein Arrays

AbstractProtein crystallization is an important tool for structural biology and nanostructure preparation. Here, we report on kinetic pathway‐dependent protein crystals that are controlled by light. Photo‐responsive crystallites are obtained by complexing the model proteins with cationic azobenzene dyes. The crystalline state is readily switched to a dispersed phase under ultraviolet light and restored by subsequent visible‐light illumination. The switching can be reversibly repeated for multiple cycles without noticeable structure deterioration. Importantly, the photo‐treatment not only significantly increases the crystallinity, but creates crystallites at conditions where no ordered lattices are observed upon directly mixing the components. Further control over the azobenzene isomerization kinetics produces protein single crystals of up to ≈50 μm. This approach offers an intriguing method to fabricate metamaterials and study optically controlled crystallization.

Plasma immobilization of azobenzene dye on polyamide 6 polymer

Plasma treatment of polymeric materials is a cost-effective and efficient technique to modify the surface and change the constituent unit configuration. This research investigates the effects of argon DC glow discharge plasma on pure and DR1 dye-loaded polyamide 6 polymer films and stabilization of dye on the surface. Plasma breaks some bonds and activates the surface through creating reactive structures such as free radical sites on the surface and increases tertiary amides on the surface of polymer. Besides, this process alters surface topographical characteristics and conformation of azobenzene dye which are effective on the durability of the dye on the surface. Plasma causes interactions of the dye with the polymer and immobilizes the dye on the polymer. On the other hand, these interactions lead to changes in the dye's optical and geometric isomeric activity and stability. This work studies the chemical and morphological changes of polyamide 6 by plasma with AFM and spectroscopic methods. Furthermore, the aging of nylon 6 films loaded with DR1 dye is measured, and the conformational changes of the dye are investigated. Plasma stabilizes the dye on the polymer surface through making changes of chemical and physical properties on the surface components.

Effect of Disperse Red 1 Azobenzene Dye Doping and Annealing on the Thermomechanical and Photomechanical Properties of PMMA Fibers

This work studies the effect of azobenzene dye Disperse Red 1 (DR1) doping and annealing on the thermomechanical and photomechanical properties of poly(methyl methacrylate) (PMMA) fibers. The mechanical properties are measured as a function of temperature, pump light intensity, and polarization. We find that doping with DR1 increases the stiffness and the glass transition temperature (Tg) of the PMMA fibers. Moreover, annealing below Tg decreases Young’s modulus and increases Tg. Finally, the photothermal heating contribution to the photomechanical response and the length change during laser exposure are determined in both unannealed and annealed plain PMMA and DR1-doped PMMA fibers. We find that photothermal heating is the dominant mechanism and the effect of photoisomerization is negligible. The temperature-dependent photomechanical efficiencies are also determined.

Photothermal and Reorientational Contributions to the Photomechanical Response of DR1 Azo Dye-Doped PMMA Fibers

This work is a comprehensive experimental and theoretical study aimed at understanding the photothermal and molecular shape-change contributions to the photomechanical effect of polymers doped with azo dyes. Our prototypical system is the azobenzene dye Disperse Red 1 (DR1) doped into poly (methyl methacrylate) (PMMA) polymer formed into optical fibers. We start by determining the thermo-mechanical properties of the materials with a temperature-dependent stress measurement. The material parameters, so determined, are used in a photothermal heating model—with no adjustable parameters—to predict its contribution. The photothermal heating model predicts the observations, ruling out mechanisms originating in light-induced shape changes of the dopant molecules. The photomechanical tensor response along the two principle axes in the uniaxial approximation is measured and compared with another independent theory of photothermal heating and angular hole burning/reorientation. Again, the results are consistent only with a purely thermal response, showing that effects due to light-induced shape changes of the azo dyes are negligible. The measurements are repeated as a function of polymer chain length and the photomechanical efficiencies determined. We find the results to be mostly chain-length independent.

Photocontrolled capacitive biosensor based on photoresponsive azobenzene-doped liquid crystals for label-free protein assay

Azobenzene-doped liquid crystals (ADLCs) have found widespread applications in fields such as holographic technology, photoactuators, and smart windows, but their potential in biosensing has not been explored. In this study, ADLCs were prepared by doping the nematic liquid crystal (LC) host E7 with a photochromic azobenzene dye ChAD-3C-S, which, upon exposure to ultraviolet (UV) light, underwent trans - cis photoisomerization and induced the phase transition of ADLCs from the cholesteric to the nematic state. The isomerization and phase transition are reversed when the nematic ADLCs are irradiated with green light. A biosensing platform based on the photoresponsive ADLCs for the detection and quantitation of bovine serum albumin (BSA) at the LC-glass interface was constructed by assembling a sandwiched LC cell with a pair of glass substrates modified with the homeotropic alignment reagent dimethyloctadecyl[3-(trimethoxysilyl)propyl] ammonium chloride (DMOAP). By immobilizing BSA on one of the DMOAP-coated glass substrates, the concentration-dependent effect of the biomolecule on the physical properties of ADLCs was analyzed quantitatively through multiple modes of detection including optical texture observation under a polarizing optical microscope as well as transmission spectrometry and capacitance measurements. In the photocontrolled ADLC-based capacitive biosensor, BSA was quantitated by measuring the time-evolved capacitance of an ADLC during the trans–cis-trans isomerization of ChAD-3C-S by alternating the wavelength of incident light, which improved the limit of detection (LOD) to 8.8 × 10−3 μg/ml, an order of magnitude lower than that obtained by spectrometric analysis. Results from this study suggest that the photocontrollable and fast-response features unique to ADLCs may create new possibilities for the development of innovative LC-based biosensing technologies.

Photodynamic control of bacterial motility by means of azobenzene molecules

We demonstrate that azobenzene dye molecules, such as Methyl Orange (MO) and Acid Yellow 9 (AY9), can be used to dynamically control the motility of flagellar bacteria E. coli. We show that the speed of bacteria can be changed by light up to +23% and -45%, for different dyes. Indeed, these molecules have opposite effect: when photoexcited, the bacterial speed increases for MO and decreases for AY9. In order to understand the corresponding mechanism, the concentration dependence, toxicity, viscosity and pH of used solutions were analyzed. The viscosity and pH were found to be unchanged for both molecules in all photoexcitation conditions. The toxicity of the irradiated state of MO was found to be lower compared to its state in the dark at equilibrium. In contrast, for AY9, both states were nontoxic at the fixed pH 7, but its irradiated state was less toxic when the pH dropped with the increase of its concentration (due to the acid effect of the molecule). Our results show that the chemical interaction with bacteria is at the origin of the results obtained with MO, while the proton pump inhibition could be responsible for those with AY9.

Comment on the Determination of the Polar Anchoring Energy by Capacitance Measurements in Nematic Liquid Crystals

Capacitance measurements have been extensively used to measure the anchoring extrapolation length L at a nematic–substrate interface. These measurements are extremely delicate because the value found for L often critically depends on the sample thickness and the voltage range chosen to perform the measurements. Several reasons have been proposed to explain this observation, such as the presence of inhomogeneities in the director distribution on the bounding plates or the variation with the electric field of the dielectric constants. In this paper, I propose a new method to measure L that takes into account this second effect. This method is more general than the one proposed in Murauski et al. Phys. Rev. E 71, 061707 (2005) because it does not assume that the anchoring angle is small and that the anchoring energy is of the Rapini–Papoular form. This method is applied to a cell of 8CB that is treated for planar unidirectional anchoring by photoalignment with the azobenzene dye Brilliant Yellow. The role of flexoelectric effects and the shape of the anchoring potential are discussed.

Characterizing azobenzene disperse dyes in commercial mixtures and children's polyester clothing

Azobenzene disperse dyes are the fastest-growing class of dyestuffs, yet little is known about dye occurrences, sources, and transformations; azo dyes are also underrepresented in chemical standard catalogs, molecular databases, and mass spectral libraries. Many azo dyes are known to have sensitization, mutagenic, and carcinogenic properties. To fill these knowledge gaps, azo dyes were purified from dyestuffs by Soxhlet extraction and flash chromatography and characterized using ultra-high-performance liquid chromatography (UHPLC) coupled to a high resolution Orbitrap Fusion Lumos mass spectrometer operated in positive electrospray ionization mode, as well as by 1H and 13C NMR. Data were analyzed to identify likely chemical formulas and structures using a weight-of-evidence approach with multiple open-source, in silico computational mass spectrometry tools. Nineteen total azobenzene dyes were detected in dyestuffs via a non-targeted analysis approach; the azobenzene dyes Disperse Blue 79:1, Disperse Blue 183:1, Disperse Orange 44, Disperse Orange 73, Disperse Red 50, Disperse Red 73, and Disperse Red 354 were purified from raw dyestuffs. Samples of children's polyester clothing were then analyzed likewise. In clothing, 21 azobenzene disperse dyes were detected, 12 of which were confirmed and quantified via reference standards. Individual dyes in apparel were quantified at concentrations up to 9230 μg dye/g shirt, with geometric means ranging 7.91–300 μg dye/g shirt. Total dye load in apparel was quantified at up to 11,430 μg dye/g shirt. This research supported the development of reference standards and library mass spectra for azobenzene disperse dyes previously absent from standard and spectral libraries. By analyzing the scope and quantities of azo dyes in children's polyester apparel, this study will facilitate a more robust understanding of sources of these potentially allergenic and mutagenic compounds.

Features of the Photovoltaic Properties of Photosemiconductive Film Composites Based on a Carbazolyl-Containing Oligomer with Azobenzene Dyes as Additives

Features of the Photovoltaic Properties of Photosemiconductive Film Composites Based on a Carbazolyl-Containing Oligomer with Azobenzene Dyes as Additives

Exploring the electron-hole transport nature and optoelectronic properties of 4-nitro-4′-amino-azobenzene-based dyes

Charge transport and electronic properties of 4-nitro-4′-amino-azobenzene compounds with donor-acceptor backbone were examined at the molecular level. Optical properties of all the studied six azobenzene dyes were also explored at the solid-state bulk level, i.e., dielectric constants, conductivity, refractive index, and extinction coefficient values. The introduction of benzyl group enhances whereas propanenitrile diminishes the values for real and imaginary dielectric functions. Moreover, the substitution of 3-methoxy-3-oxopropyl and propanenitrile at amino group decreases the real conductivity values; however, bis(3-methoxy-3-oxopropyl) improves these values. These 4-nitro-4′-amino-azobenzene compounds showed good refractive indices in the energy range 0–2 eV which revealed that these dyes would be efficient to generate healthier outputs with lower energy inputs. The effect of substituents was also investigated on transfer integrals, frontier molecular orbitals (FMOs), reorganization energies, electron affinity (EA), and ionization energy (IE). The ground-state geometries were optimized by density functional theory at B3LYP/6-31G** level to probe the molecular level properties. The same level of theory was used for the cation and anion optimizations. The hole and electron transfer nature of azo dyes was investigated by evaluating the electron/hole transfer integrals (Velectron/Vhole) as well as hole and electron reorganization energy values. The results exposed that superior Vhole values of Azo2 and Azo4 might lead to these dyes as p-type contenders. Moreover, larger Velectron values of Azo1, Azo3, Azo5, and Azo6 might lead to these dyes as n-type competitors. These results revealed that inspected Azo dyes would be able to serve as competent hole and electron transfer materials within versatile organic semiconductors.

Tunable microring resonators using light-activated functional polymer coatings.

We demonstrate tunable microring resonators (TMRs) based on light-activated functional polymer coatings deposited on glass optical fibers. TMRs were fabricated using two layers of polydimethylsiloxane-based compounds: one incorporating an azobenzene dye and one using a fluorescent ytterbium and erbium-doped sodium yttrium fluoride powder. The latter yields a photoluminescent composite producing green up-conversion emission under infrared pumping. This visible emission triggers photoinduced birefringence effects in the azobenzene layer, thereby modifying the spectral features of the TMR devices. The shift in the resonance peaks as a function of pump power is linear, yielding a tuning range of 1.3 nm. Aside from the observed photoinduced effects, we also discuss the photothermal effects involved in the tuning mechanism.

Configurational Selection in Azobenzene-Based Supramolecular Systems Through Dual-Stimuli Processes.

Azobenzene is one of the most studied light‐controlled molecular switches and it has been incorporated in a large variety of supramolecular systems to control their structural and functional properties. Given the peculiar isomeric distribution at the photoexcited state (PSS), azobenzene derivatives have been used as photoactive framework to build metastable supramolecular systems that are out of the thermodynamic equilibrium. This could be achieved exploiting the peculiar E/Z photoisomerization process that can lead to isomeric ratios that are unreachable in thermal equilibrium conditions. The challenge in the field is to find molecular architectures that, under given external circumstances, lead to a given isomeric ratio in a reversible and predictable manner, ensuring an ultimate control of the configurational distribution and system composition. By reviewing early and recent works in the field, this review aims at describing photoswitchable systems that, containing an azobenzene dye, display a controlled configurational equilibrium by means of a molecular recognition event. Specifically, examples include programmed photoactive molecular architectures binding cations, anions and H‐bonded neutral guests. In these systems the non‐covalent molecular recognition adds onto the thermal and light stimuli, equipping the supramolecular architecture with an additional external trigger to select the desired configuration composition.

Fast, Light-Responsive, Metal-Like Polymer Actuators Generating High Stresses at Low Strain

Summary Producing lightweight polymeric actuators able to generate high stresses typical of hard metals and/or ceramics remains challenging. The photo-mechanical responses of ultra-drawn ultra-high molecular weight polyethylene (UHMWPE) actuators containing azobenzene photo-switches with symmetrically attached polyethylene (PE) side chains are reported. Long PE side chains promote dispersion within the apolar UHMWPE matrix, and the ultra-drawn films are highly aligned. The ultra-drawn azobenzene-doped UHMWPE films have high Young's moduli (∼100 GPa) and are viscoelastic at room temperature at strains below 1%. The photo-mechanical response of the films is fast ( 6 × 104 Pa (kg m−3)−1) to UV or visible light at a low strain (∼0.06%). The actuator responds to rotating linearly polarized light, causing a photo-induced stress wave response. Such rapid, high-stress, low-strain, photo-mechanical responses are unique in soft polymer systems with physical values approaching hard metals/ceramics.

New material based on polyurethane doped with azobenzene dyes in recording media for dynamic polarization holography

New material based on polyurethane doped with azobenzene dyes in recording media for dynamic polarization holography