Azo Molecules Research Articles

Visible-Light-Induced Reversible Photochemical Crystal–Liquid Transitions of Azo-Switches for Smart and Robust Adhesives

Photochemical crystal ↔ liquid transitions (PCLTs) are interesting phenomena that couple reversible photochemical transformations with thermophysical phase transitions. A potential application of PCLTs is the development of photoresponsive smart materials capable of exerting reversible adhesion capacities on specific surfaces at a desired timing, which are unattainable for conventional adhesives. However, PCLT-based adhesives generally use UV light as the stimulus, which could lead to degradation of materials and health problems. Here, visible-light-controlled smart and robust adhesives are developed using small-molecule azo photoswitches. These azo molecules can undergo very efficient trans-crystal → cis-liquid and cis-liquid → trans-crystal transitions under 405 and 532 nm light irradiations, respectively. Their trans-crystal state displays strong adhesion strengths on various substrates, e.g., 1.13 MPa on quartz/quartz and 1.58 MPa on wood/wood, and very fast light-induced separation of glued substrates can be accomplished within 1 s along with the loss of adhesion strength in the cis-liquid state. Robust switching of the adhesion strength is demonstrated in multiple cycles, and these adhesives can also work well in underwater environments. Visible-light-controlled reversible PCLTs can be a very promising strategy in the pursuit of high-performance photoresponsive adhesives.

Alkyl substituent-dependent systematic change in cold crystallization of azo molecules.

The thermal behavior of alkyl-derivatized 1-(2,4-dimethylphenylazo)-4-naphthol and 1-(2,4-dimethylphenylazo)-2-naphthol (2,4-DM-4-Cn and 2,4-DM-2-Cn, respectively) was investigated. The change in the position of the alkyl substituent led to a variation in the thermal behavior, including the cold crystallization, which is a heat-storing phenomenon. In addition, a comprehensive study of the alkyl chain length revealed that 2,4-DM-4-Cn had better crystallinity and exhibited cold crystallization with short alkyl chains. The π–π, C–H⋯N, and C–H⋯π interactions stabilized the crystal structure of 2,4-DM-4-Cn. On the other hand, the polymorphism of 2,4-DM-2-Cn inhibited the formation of a uniform crystalline phase during cooling, which led to poor crystallinity. The only difference between the compounds, the position of the substituent, resulted in a clear variation in the cold crystallization and heat storage properties.

Light-Controlled Asymmetric Dual-S-Taper Fiber Interferometer Integrated With Ethyl Orange Solution Under 473 nm Laser Illumination

An azobenzene (azo)-integrated asymmetric dual-S-taper fiber interferometer based on concatenated single-mode fiber S-tapers is proposed and fabricated. As the fiber interferometer is immersed into the ethyl orange (EO) solution, due to the photo-isomerization effect of azo materials, azo molecules would experience conformal change when 473 nm laser illumination is applied, resulting in the variation of ambient surrounding refractive index. Transmission spectra of the proposed dual-S-taper structure exhibit stable and regular wavelength shift under different illumination light intensities or EO weight percentages of EO solutions. An optimal EO weight percentage of 0.1 wt% was experimentally acquired with wavelength sensitivity reaching −27.6 pm/mW for a laser power range of 0 mW to 195 mW. Furthermore, repeated laser power increasing and decreasing experiments and the control experiment under the distilled water environment proves our proposed fiber interferometer with highly reversible and stable light-sensitive wavelength responses, making it a good candidate for light intensity sensing and light-controlled wavelength-tuning applications in future all-optical networking systems.

Light-Induced Modulation of Chiral Functions in G-Quadruplex-Photochrome Systems.

The design of artificially engineered chiral structures has received much attention, but the implementation of dynamic functions to modulate the chiroptical response of the systems is less explored. Here, we present a light-responsive G-quadruplex (G4)-based assembly in which chirality enrichment is induced, tuned, and fueled by molecular switches. In particular, the mirror-image dependence on photoactivated azo molecules, undergoing trans-to-cis isomerization, shows chiral recognition effects on the inherent flexibility and conformational diversity of DNA G4s having distinct handedness (right- and left-handed). Through a detailed experimental and computational analysis, we bring compelling evidence on the binding mode of the photochromes on G4s, and we rationalize the origin of the chirality effect that is associated with the complexation event.

Fabrication of polymeric solar thermal fuel composite for solar energy storage applications

AbstractSolar energy storage and conversion have remained significant global challenges. This article discusses how to fabricate a polymeric solar thermal fuel (P‐STF) composite with unique thermal storage abilities. In this regard, we aim at developing a novel method for dispersing multi‐walled carbon nanotubes (MWCNTs) functionalized with azobenzene molecules (modified azobenzene molecules) in ethylene‐vinyl acetate (EVA). The modification of azobenzene (functionalization) enhances the energy storage density of AZO molecules, and the addition of fillers (MWCNT) leads to the production of the P‐STF composite with the potential to store and convert solar energy to thermal energy. The differential scanning calorimetry (DSC) test verifies the P‐STF composite's capacity to absorb solar energy and release it as heat. Thus, the uncharged nanocomposites required heat energy at the melting point temperature of EVA (Enthalpy 18.392 J/g). However, the EVA‐AZO‐MWCNT 10% and EVA‐AZO‐MWCNT 5% nanocomposites released heat energy rather than requiring it to melt with enthalpy −37.6526 and −1.2609 J/g, respectively, which indicates the heat release in the P‐STF composite. Moreover, oscillatory shear rheological measurement (RMS) and field emission scanning electron microscopy (FESEM) demonstrate that modified azobenzene (MWCNT‐AZO) is well dispersed in the polymer matrix (EVA).

Heterocyclic azo dyes derived from 2-(6-chloro-1,3-benzothiazol-2-yl)-5-methyl-2,4-dihydro-3H-pyrazol-3-one having benzothiazole skeleton: Synthesis, structural, computational and biological studies

A series of novel benzothiazole based azo dyes were synthesized by diazotization of various substituted anilines coupling with 2-(6-chloro-1,3-benzothiazol-2-yl)-5-methyl-2,4-dihydro-3H-pyrazol-3-one by the diazo-coupling reaction at 0-5 °C. The structural confirmation of the synthesized molecules was carried out by spectroscopic techniques such as UV-visible, FT-IR and 1H NMR, respectively and by theoretical methods. Further, the computational studies were employed to interpret the structural properties of the azo molecules by using B3LYP program at 6-31G (d, p) basis set. Furthermore, the synthesized compounds were screened against cell lines to reveal their cytotoxic property, results revealed moderate to good cytotoxic potential of few compounds.

Azobispyrazole Family as Photoswitches Combining (Near‐) Quantitative Bidirectional Isomerization and Widely Tunable Thermal Half‐Lives from Hours to Years**

AbstractAzobenzenes are classical molecular photoswitches that have been widely used. In recent endeavors of molecular design, replacing one or both phenyl rings with heteroaromatic rings has emerged as a strategy to expand molecular diversity and access improved photoswitching properties. Many mono‐heteroaryl azo molecules with unique structures and/or properties have been developed, but the potential of bis‐heteroaryl architectures is far from fully exploited. We report a family of azobispyrazoles, which combine (near‐)quantitative bidirectional photoconversion and widely tunable Z‐isomer thermal half‐lives from hours to years. The two five‐membered rings remarkably weaken the intramolecular steric hindrance, providing new possibilities for engineering the geometric and electronic structure of azo photoswitches. Azobispyrazoles generally exhibit twisted Z‐isomers that facilitate complete Z→E photoisomerization, and their thermal stability can be broadly adjusted regardless of the twisted shape, overcoming the conflict between photoconversion (favored by the twisted shape) and Z‐isomer stability (favored by the orthogonal shape) encountered by mono‐heteroaryl azo switches.

Azobispyrazole Family as Photoswitches Combining (Near-) Quantitative Bidirectional Isomerization and Widely Tunable Thermal Half-Lives from Hours to Years*.

Azobenzenes are classical molecular photoswitches that have been widely used. In recent endeavors of molecular design, replacing one or both phenyl rings with heteroaromatic rings has emerged as a strategy to expand molecular diversity and access improved photoswitching properties. Many mono-heteroaryl azo molecules with unique structures and/or properties have been developed, but the potential of bis-heteroaryl architectures is far from fully exploited. We report a family of azobispyrazoles, which combine (near-)quantitative bidirectional photoconversion and widely tunable Z-isomer thermal half-lives from hours to years. The two five-membered rings remarkably weaken the intramolecular steric hindrance, providing new possibilities for engineering the geometric and electronic structure of azo photoswitches. Azobispyrazoles generally exhibit twisted Z-isomers that facilitate complete Z→E photoisomerization, and their thermal stability can be broadly adjusted regardless of the twisted shape, overcoming the conflict between photoconversion (favored by the twisted shape) and Z-isomer stability (favored by the orthogonal shape) encountered by mono-heteroaryl azo switches.

Recent Applications of Azo Dyes: A Paradigm Shift from Medicinal Chemistry to Biomedical Sciences.

Azo molecules possess the characteristic azo bond (-N=N-) and are considered fascinating motifs in organic chemistry. Since the last century, these brightly colored compounds have been widely employed as dyes across several industries in applications for printing, food, paper, cosmetics, lasers, electronics, optics, material sciences, etc. The discovery of Prontosil, an antibacterial drug, propelled azo compounds into the limelight in the field of medicinal chemistry. Subsequent discoveries including Phenazopyridine, Basalazide, and Sulfasalazine enabled azo compounds to occupy a significant role in the drug market. Furthermore, azo compounds have been employed as antibacterial, antimalarial, antifungal, antioxidant, as well as antiviral agents. The metabolic degradation of many azo dyes can induce liver problems if ingested, posing a safety concern and limiting their application as azo dyes in medicinal chemistry. However, azo dyes remain particularly significant for applications in cancer chemotherapy. Recently, a paradigm shift has been observed in the use of azo dyes: from medicinal chemistry to biomedical sciences. The latter benefits from azo dye application are related to imaging, drug delivery, photo-pharmacology and photo switching. Herein, we have compiled and discussed recent works on azo dye compounds obtained so far, focusing on their medicinal importance and future prospects.

Synthesis, Characterization and Theoretical Calculations of a Novel Azo Derivative with In Vitro and In Silico Biological Studies

An azo molecule, 2,2-dimethyl-5-(m-tolyldiazenyl)-1,3-dioxane-4,6-dione (DTDD), was designed, synthesized and evaluated for its antibacterial potential. The structure of the DTDD was confirmed by 1H-NMR, 13C-NMR, FT-IR and UV–Vis spectra. The molecular geometry and vibrational frequency calculations of the DTDD in the ground state were performed by the density functional theory (DFT) employing the B3LYP level with the 6-311G(d,p) basis set. 1H-NMR and 13C-NMR chemical shifts were calculated by using the gauge independent atomic orbital (GIAO) method. Electronic property and HOMO–LUMO calculations were carried out by a time-dependent DFT (TD-DFT) approach. The calculated spectroscopic values for the DTDD were in very good agreement with experimental ones. Besides, in vitro antibacterial activity of the DTDD was studied against five different bacterial cultures. DTDD showed antibacterial activity with an MIC range of 62.5–500 µg/mL. The best antibacterial activity was found with 62.5 µg/mL against S. aureus. Additionally, molecular docking studies against β-ketoacyl-acyl carrier protein synthase III (KAS III) and lipoteichoic acid synthase (LtaS) were performed. According to the binding energy (− 7.67 kcal/mol) and full fitness score (− 2391.78), the ligand had a better orientation with LtaS. Druglikeness and ADME parameters were also calculated and the TPSA value was found to be 76.99 A2. The calculated values showed that DTDD had good oral drug candidate properties.

Structure and Elastic Properties of an Unsymmetrical Bi-Heterocyclic Azo Compound in the Langmuir Monolayer and Langmuir-Blodgett Film.

We study the structure and elastic properties of the bi-heterocyclic azo compound at the air–water interface through surface pressure (π)–area (A) isotherm recording followed by transferring them on hydrophilic and hydrophobic Si surfaces by the Langmuir–Blodgett (LB) deposition method. A substantial change in the area/molecule is observed as a function of subphase pH and temperature. Such parameters strongly influence intramolecular interactions within azo molecules and the interactions between azo molecules and water that manifested in higher surface activity at low temperature and high pH, which in turn modifies the elasticity of azo assembly at the air–water interface. A large pH-dependent hysteresis with negative change in entropy, indicating molecular rearrangements, is observed. Molecular assembly formed at the air–water interface is then transferred onto hydrophilic and hydrophobic Si surfaces at two different surface pressures (5 and 30 mN/m) by the LB technique. The structural analysis performed by X-ray reflectivity and atomic force microscopy techniques suggests that the LB films exhibit an abrupt layered structure on hydrophilic Si, whereas an overall rough film is formed on hydrophobic Si. The coverage and compactness of individual layers are found to increase with the deposition pressure (5 to 30 mN/m).

Thermocapillary Marangoni Flows in Azopolymers.

It is well known that light-induced multiple trans-cis-trans photoisomerizations of azobenzene derivatives attached to various matrices (polymeric, liquid crystalline polymers) result in polymer mass movement leading to generation of surface reliefs. The reliefs can be produced at small as well as at large light intensities. When linearly polarized light is used in the process, directional photo-induced molecular orientation of the azo molecules occurs, which leads to the generation of optical anisotropy in the system, providing that thermal effects are negligible. On the other hand, large reliefs are observed at relatively strong laser intensities when the optofluidization process is particularly effective. In this article, we describe the competitive thermocapillary Marangoni effect of polymer mass motion. We experimentally prove that the Marangoni effect occurs simultaneously with the optofluidization process. It destroys the orientation of the azopolymer molecules and results in cancelation of the photo-induced birefringence. Our experimental observations of polymer surface topography with atomic force microscopy are supported by suitable modelings.

Control of third-order nonlinear optical properties by coordination metal change based on a series of metal organic chains

The research on the third-order nonlinear optics (NLO) materials have attracted more and more attention. In this work, an organic ligand (H2L) containing azo phenyl group and coordination N atom is selected. The presence of NN increases the fluidity of electrons in the azo molecule, which greatly improves the third-order nonlinearity. Furthermore, we synthesized three H2L-based metal complexes [Mn(L)(H2O)4]n (1), [Zn(L)(H2O)2]n (2) and [Cd(L)(H2O)4]n (3) and their nonlinear performances was also measured using Z-scan technology. The results show that the coordination bond between metal ions and the ligand changes the delocalization of the whole systems, resulting in changed the nonlinear performances. The calculation of density functional theory (DFT) confirms that the Mn2+ and Zn2+ addition is not obvious to influence NLO, and the addition of Cd2+ makes the non-linear signal weaken. The reason may result from the valence layer electron configuration of the different metal ions.

Triazole based azo molecules as potential antibacterial agents: Synthesis, characterization, DFT, ADME and molecular docking studies

In this study, three triazole based azo molecules [3-amino-4-[1H-1,2,4-triazole-3-yldiazenyl]-1H-pyrazole-5-ol (1), 3-[(3,5-dimethyl-1H-pyrazole-4-yl)diazenyl]-1H-1,2,4-triazole (2) and 4-[1H-1,2,4-triazole-3yldiazenyl]benzene-1,3-diol (3)] were, synthesized and characterized by using 1H NMR, FT-IR, UV–vis and mass spectra. The molecular structure, vibrational spectroscopic data, electronic transition absorption wavelengths, HOMOs and LUMOs analyses, molecular electrostatic potential (MEP) and potential energy surface (PES) diagrams were calculated by using DFT/B3LYP method with 6-311G(d,p) basis set. NMR chemical shift calculations were performed by using the gauge-invariant atomic orbital (GIAO) method. The spectroscopic results obtained from quantum chemical calculations of the 1, 2 and 3 molecules were in good agreement with the experimental data. Antibacterial activities of the 1, 2 and 3 were investigated against four different bacterial cultures. Although 1 molecule did not show very good antibacterial activity, 2 and 3 showed good activity against Staphylococcus aureus at a MIC of 250 and 62.5 μg/mL, respectively. Druglikeness and some of the pharmacokinetic properties of the 1, 2 and 3 were also examined. In addition, molecular docking studies were performed to investigate the antibacterial properties of synthesized compounds by in silico method. For this purpose, β-ketoacyl-acyl carrier protein (ACP) synthase III (KAS III) and lipoteichoic acid synthase (LtaS) inhibitory properties of 1, 2 and 3 molecules were investigated. Although all of the synthesized compounds showed antibacterial properties according to the results of the molecular docking studies, the best results were obtained by the compound 3 which interacts with both KAS III and LtaS with binding energy of −7.17 and −7.53 kcal/mol, respectively.

Accurate Prediction of the S1 Excitation Energy in Solvated Azobenzene Derivatives via Embedded Orbital-Tuned Bethe-Salpeter Calculations.

By employing the Bethe-Salpeter formalism coupled with a nonequilibrium embedding scheme, we demonstrate that the paradigmatic case of S1 band separation between cis and trans in azobenzene derivatives can be computed with excellent accuracy compared to experimental optical spectra. Besides embedding, we show that the choice of the Kohn-Sham exchange correlation functional for DFT is critical, despite the iterative convergence of GW quasiparticle energies. We address this by adopting an orbital-tuning approach via the global hybrid functional, PBEh, yielding an environment-consistent ionization potential. The vertical excitation energy of 20 azo molecules is predicted with a mean absolute error as low as 0.06 eV, up to three times smaller compared to standard functionals such as M06-2X and PBE0, and five times smaller compared to recent TDDFT results.

Synthesis, characterization and pharmacological evaluation of 2-aminothiazole incorporated azo dyes

Azo molecules (A1-A3) were prepared by reacting 2-aminothiazole with three different pyridone derivatives as coupling components, viz., 6-hydroxy-4-methyl-2-oxo-1,2-dihydropyridine-3-carbonitrile, 6-hydroxy-1,4-dimethyl-2-oxo-1,2-dihydropyridine-3-nitrile and 1-ethyl-6-hydroxy-4-methyl-2-oxo-1,2-dihydropyridine-3-carbonitrile via diazo-coupling reactions, under appropriate experimental conditions. The structural characteristics of the synthesized compounds were checked by different spectral techniques. The newly synthesized molecules were tested for their biological activities and the results of biological activity studies of the compounds prepared exhibited potential antimicrobial activity against the respective microorganisms. The synthesized azo dyes also demonstrated promising antimycobacterial activity screened against M. tuberculosis. All the compounds showed considerable cleavage efficiency against supercoiled pBR322 DNA. Further, the in silico molecular docking study was performed against E. coli 24 kDa domain and Cyp51 (cytochrome P450 14α-sterol demethylase) as target receptors. The binding energy of each studied compound was evaluated, and the data revealed that the compound A1 displayed higher binding affinity value and forms hydrogen bonds with the active amino acids.

CO2 permeability control in 3D printed light responsive structures

Azobenzene cromophores are proposed as functional dyes for the development of smart DLP-3D printable formulations. Two different azo molecules have been tested for the fabrication of membranes; taking advantage of the photoisomerization of these compounds, light induced changes in CO2 permeability have been studied showing a great increase of gas transmission upon green light irradiation. The investigations showed a linear increase of permeability with the increase of laser intensity, enabling a fine control of gas permeation. Moreover, these materials showed selectivity toward different gases, enabling a great increase of permeation upon laser irradiation for CO2 but not for O2. The use of the dye during the DLP printing process is necessary to confine the light inside the exposed layer allowing a precise printability without over-exposures; in this way complex architectures can be built and, at the same time, the choice of a molecule with intrinsic functionality transfers this functional property to the object. In the present study 3D structures presenting light triggered CO2 permeability have been built; as a proof of concept a smart 3D photocontrollable valve has been produced.

Hydrogen Bonding-Induced Assembled Structures and Photoresponsive Behavior of Azobenzene Molecule/Polyethylene Glycol Complexes.

We investigated the self-assembled structures and photoresponsive and crystallization behaviors of supramolecules composed of 4-methoxy-4′-hydroxyazobenzene (Azo) molecules and polyethylene glycol (PEG) that were formed through hydrogen-bonding interactions. The Azo/PEG complexes exhibited the characteristics of photoresponse and crystallization, which originated from Azo and PEG, respectively. When Azo/PEG complexes were dissolved in solvents, hydrogen-bonding interaction hindered the rotation and inversion of mesogens, causing a reduction in the photoisomerization rate compared with the photoisomerization rate of the neat Azo. The confinement of Azo/PEG complexes in thin films further resulted in a substantial decrease in the photoisomerization rate but an increase in the amounts of H-aggregated and J-aggregated mesogens. Regarding PEG crystallization, ultraviolet irradiation of Azo/PEG complexes increased the quantity of high-polarity cis isomers, which improved the compatibility between mesogens and PEG, subsequently increasing the crystallization temperature of PEG. Moreover, the complexation of Azo and PEG induced microphase separation, forming a lamellar morphology. Within the Azo-rich microphases, mesogens aggregated to form tilted monosmectic layers. By contrast, PEG crystallization within the PEG-rich microphases was hard confined, indicating that the domain size of the lamellar morphology was unchanged during PEG crystallization.

Adjusting Fermi Level of Graphene by Controlling the Linker Lengths of Dipolar Molecules.

Graphene modified by azo molecules has attracted much attention due to its promising graphene-enhanced Raman scattering (GERS) effect. Herein, we achieved the shortened distance between the dipole moment and graphene, by reducing the number of methylene groups and the chain length, and studied the Raman scattering in dipolar molecules/graphene hybrids. Whether for low or high concentrations, a more significant GERS signal can be observed, which can be attributed to the effective modulation of the dipole moment on interface energy level matching. Further, by fabricating FET devices, we demonstrate more obvious p-type and n-type doping in graphene that is affected by the chain length of the azobenzene molecule. On the basis of the dependence of the G band shift on the Fermi surface change, we further reveal the important role of dipole moment distance in dipolar molecules/graphene hybrids. These studies provide a new approach to optimize the interface matching between azobenzene and graphene and may help achieve more sensitive GERS detection.

Optically reversible deformation of azobenzene particles prepared by a colloidal method

Optical reversibility of deformation of azobenzene particles prepared by a colloidal method is demonstrated. Linearly polarized laser light modifies the shape of the azo particles through photoisomerization of the azo molecules. We found that the oblique incidence of a single laser beam can reversibly deform the azo particles into shapes, including spherical, elliptical, and rod shapes, through simple adjustment of the polarization direction and irradiation time of the laser light. The direction of the long axis of the ellipsoid was sequentially controlled by selecting the polarization direction of obliquely incident laser light, although the normal incidence never rotated the ellipsoidal direction under any polarization direction. The reversibility of the changes in the azo particle shape was confirmed in cyclic optical deformation experiments.