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Azobenzene photoswitches are valuable tools for controlling properties of molecular systems with light. We have been investigating azobenzene glycoconjugates to probe carbohydrate‐protein interactions and to design glycoazobenzene macrocycles with chiroptical and physicochemical properties modulated by light irradiation. To date, direct conjugation of glycosides to azobenzenes was performed by reactions providing target compounds in limited yields. We therefore sought a more effective and reliable coupling method. In this paper, we report on a straightforward thioarylation of azobenzene derivatives with glycosyl thiols as well as other thiols, thereby increasing the scope of azobenzene conjugation. Even challenging unsymmetrical conjugates can be achieved in good yields via sequential or one‐pot procedures. Importantly, red‐shifted azoswitches, which are addressed with visible light, were easily functionalized. Additionally, by oxidation of the sulfide bridge to the respective sulfones, both the photochromic and the thermal relaxation properties of the core azobenzene can be tuned. Utilizing this option, we realized orthogonal three‐state photoswitching in mixtures containing two distinct azobenzene thioglycosides. [ABSTRACT FROM AUTHOR]

Azobenzene derivatives have become one of the most famous photoresponsive chromophores in the past few decades for their reversible molecular switches upon the irradiation of actinic light. To meet the ever-increasing requirements for applications in materials science, biomedicine, and light-driven devices, it is usually necessary to adjust their photochemical property from the molecular level by changing the substituents on the benzene rings of azobenzene groups. Among the diverse azobenzene derivatives, azopyridine combines the photoresponsive feature of azobenzene groups and the supramolecular function of pyridyl moieties in one molecule. This unique feature provides pH-responsiveness and hydrogen/halogen/coordination binding sites in the same chromophore, paving a new way to prepare multi-functional responsive materials through non-covalent interactions and reversible chemical reactions. This review summarizes the photochemical and photophysical properties of azopyridine derivatives in supramolecular states (e.g., hydrogen/halogen bonding, coordination interactions, and quaternization reactions) and illustrates their applications from photoresponsive liquid crystals to light-driven devices. We hope this review can highlight azopyridine as one more versatile candidate molecule for designing novel photoresponsive materials towards light-driven applications. [ABSTRACT FROM AUTHOR]

Azobenzene has attracted substantial attention as a photoswitchable molecule since its applications range from energy and data storage to biomedical applications. This work reports a new type of thin‐film based on azobenzene derivative anchored to cerium oxide nanoparticles CeO2NPs for photoswitching applications. The trans–cis isomerization and reverse isomerization occur by UV‐light exposure and thermal relaxation process, respectively. The photoisomerization and reverse isomerization kinetics for CeO2NPs‐MR thin films are studied, investigated, and analyzed using UV‐Vis absorbance spectra, FTIR spectroscopy, XRD, and scanning electron microscopy (SEM), in addition to differential scanning calorimetry (DSC) measurement to study the energy storage capacity. The results found that anchoring azobenzene to CeO2NPs is successful in multisource storage of solar energy applications. [ABSTRACT FROM AUTHOR]

Stimulus‐responsive photoluminescence (PL) materials have attracted attention because of their broad applicability in recording, switching and sensing devices. However, the development of PL materials controllable by a light stimulus remains a challenging task. Here, we demonstrate novel organic crystals of a naphthalene‐functionalized azobenzene derivative (NA) that exhibit reversible PL properties upon light and heat stimulation. The azobenzene derivative exhibits aggregation‐induced emission (AIE) in the orange PL region upon crystallization. Upon photoirradiation, the crystal transforms into an aggregate with low crystallinity via trans‐to‐cis photoisomerization. Therefore, the PL color changes from orange to yellow when the orderly aggregated NAs are converted into randomly aggregated NAs. Furthermore, the original orange PL can be recovered upon heating and cooling the photoirradiated crystal as a result of cis‐to‐trans thermal back‐isomerization. [ABSTRACT FROM AUTHOR]

Azobenzene-based molecules show unique trans-cis isomerization upon ultraviolet light irradiation, which induce the change of polarity, crystallinity, stability, and binding affinity with pharmacological target. Moreover, azobenzene is the substrate of azoreductase that is often overexpressed in many pathological sites, e.g. hypoxic solid tumor. Therefore, azobenzene can be a multifunctional molecule in material science, pharmaceutical science and biomedicine because of its sensitivity to light, hypoxia and certain enzymes, hence showing potential application in site-specific smart therapy. Herein we focus on the employment of azobenzene and its derivatives for engineering triggered prodrugs and drug delivery systems, and provide an overview of photoswitchable azo-based prodrugs, the associated problems regarding the reversible isomerization and tissue penetration of ultraviolet (UV) light, as well as the potential solutions. We also present the advance of azo-bearing delivery vehicles wherein azobenzene acts as the linker, capping agent, and building block, and discuss the corresponding mechanisms for controlled cargo release, endocytosis enhancement and sensitization of free radical cancer therapy. [Display omitted] • Azobenzene is intrinsicallysensitive to light, hypoxia and certain enzymes. • Azobenzene-based prodrugs in beneficial to reduce the adverse effects to healthy organs. • Azobenzene is an excellent building block for engineering triggered drug delivery systems. [ABSTRACT FROM AUTHOR]

Low molecular weight thiols (biothiols) are highly active compounds extensively involved in human physiology. Their abnormal levels have been associated with multiple diseases. In recent years, major efforts have been devoted to developing new nanosensing methods for the low cost and fast quantification of this class of analytes in minimally pre-treated samples. Herein, we present a novel strategy for engineering a highly efficient surface-enhanced Raman scattering (SERS) spectroscopy platform for the dynamic sensing of biothiols. Colloidally stable silver nanoparticles clusters equipped with a specifically designed azobenzene derivative (AzoProbe) were generated as highly SERS active substrates. In the presence of small biothiols (e.g., glutathione, GSH), breakage of the AzoProbe diazo bond causes drastic spectral changes that can be quantitatively correlated with the biothiol content with a limit of detection of ca. 5 nM for GSH. An identical response was observed for other low molecular weight thiols, while larger macromolecules with free thiol groups (e.g., bovine serum albumin) do not produce distinguishable spectral alterations. This indicates the suitability of the SERS sensing platform for the selective quantification of small biothiols. [ABSTRACT FROM AUTHOR]

Two new tetra-(ortho)substituted azobenzene derivatives bearing 3,5-dimethoxy groups in one of the aromatic rings and either 2,6-dimethyl or 2,6-dichloro groups in another one have been prepared and fully characterized, including by X-ray crystal structure analysis. Both compounds have twisted conformations with intramolecular possibly attractive short O–N contacts. Multiparametric correlation analysis of the absorption maxima in the UV-Vis spectra of both compounds in 17 solvents demonstrates that predominant factors in the solvatochromic properties of neutral molecules are the solvent basicity and polarity inducing bathochromic shifts of the π–π* bands. On the contrary, the absorption maxima of the protonated forms show hypsochromic shifts on increase in the solvent polarity. Spectrophotometric titrations in water reveal high basicity of both compounds with pKa values of their conjugated acids in the range from 6 to 7. Besides protonation, an efficient complexation of the di-methylated derivative with metal ions (Cu2+, Zn2+) in water is observed. Studies of photo-induced trans–cis isomerization of the new compounds demonstrates unusual solvent dependence of the rate of cis-to-trans thermal isomerization decreasing with increase in the solvent polarity. This may indicate a specific isomerization mechanism for ortho-substituted azobenzenes. Both new compounds undergo trans-to-cis isomerization with green light irradiation. [ABSTRACT FROM AUTHOR]

Inspired by human vision, a diverse range of light‐driven molecular switches and motors have been developed for fundamental understanding and application in material science and biology. Recently, the design and synthesis of visible light‐driven molecular switches and motors have been actively pursued. This emerging trend is partly motivated to avoid the harmful effects of ultraviolet light, which was necessary to drive the classical molecular switches and motors at least in one direction, impeding their employment in biomedical and photopharmacology applications. Moreover, visible light‐driven molecular switches and motors are demonstrated to enable benign optical materials for advanced photonic devices. Therefore, during the past several years, visible light‐driven molecular switches based on azobenzene derivatives, diarylethenes, 1,2‐dicyanodithienylethenes, hemithioindigo derivatives, iminothioindoxyls, donor‐acceptor Stenhouse adducts, and overcrowded alkene based molecular motors have been judiciously designed, synthesized, and used in the development of functional materials and systems for a wide range of applications. In this Review, we present the recent developments toward the design of visible light‐driven molecular switches and motors, with their applications in the fabrication of functional materials and systems in material science, bioscience, pharmacology, etc. The visible light‐driven molecular switches and motors realized so far undoubtedly widen the scope of these interesting compounds for technological and biological applications. We hope this Review article could provide additional impetus and inspire further research interests for future exploration of visible light‐driven advanced materials, systems, and devices. [ABSTRACT FROM AUTHOR]

Azobenzene has two configurations which are trans-configuration and cis-configuration. As a photo-isomerization molecule, azobenzene can transfer from trans-configuration in low energy state to cis-configuration in a high energy state under the irradiation of ultraviolet light (UV), which is the process of photo-isomerization. Herein, azobenzene and its derivatives are used in different industries and fields. However, due to their low energy density compared with other molecular solar thermal energy storage (MOST) like anthracene and norbornadiene, their applications in energy storage are influenced severely. The purpose of this paper is to find a method to solve the problem above. In this paper, 4-nitro-4′- aminoazobenzene (Azo) was grafted onto reduced graphene oxide (rGO) by the coupling reaction and then interacted with ZnCl2 to get the azobenzene graphene composite with zinc ion interaction (AGO/Zn). There are two mechanisms of energy storage/release in this method, photoisomerization of azobenzene onto graphene template, and ion interaction formation/destruction, which is a unique attempt to improve energy density through multiple mechanisms of heat release. It has been proved that the nanoscale templates have a significant effect on improving the energy density of azobenzene derivatives. FT-IR spectroscopy show that AGO/Zn is successfully prepared by this method. Moreover, the maximum energy density of that is up to 504.2 J/g under the irradiation of UV (365 nm) for 4 h, which is about 1.69 times of the azobenzene graphene composite (AGO) without ion interaction. Results show that the introduction of zinc and graphene templates greatly improves the energy density of azobenzene, which provides a reference for the development and application of azobenzene composites with multiple mechanisms of energy storage in the future. [ABSTRACT FROM AUTHOR]

Photochromic hydrogen-bonded organic frameworks (HOFs) can introduce different luminescent functional groups to achieve synergistic controlled multiple color change properties, which are in great demand for diverse information encryption applications. We report in this paper switchable photochromic and photoluminescent dual luminescent functional group HOFs constructed with synergistic effects by N , N '-bis(2-phenylalanine)-1,4,5,8-naphthalenediimine (H 2 PheNDI) and benzenecarboximidamide 4,4'-azobis(hydrochloride) (AZBH). The crystal powder of iHOF-41 is orange-red in color, which can be changed to black under the irradiation of a 365 nm ultraviolet (UV) light source for 15 min. The photoisomerization rate of the crystal solution under continuous UV irradiation for 5 h was close to 99%. The composite membranes can achieve the properties of photochromism and photoluminescence when they are discolored under 365 nm UV irradiation and, at the same time, excite red bright fluorescence. This work achieves the construction of HOFs based on switching biluminescent functional groups and explores the synergistic mechanism of the photoisomerization process and photochromism as well as its practical application in information encryption.

To explore new cavity functions, we herein employed cis‐trans stereoisomers with a N=N, C=C, or C=N unit as guest indicators for a polyaromatic capsule. Thanks to the rigid, spherical cavity with a diameter of ∼1 nm, azobenzene and stilbene derivatives are quantitatively encapsulated by the capsule with 100 % cis‐selectivity in water. The isomerization of the cis‐azo compound is suppressed against heat and light in the cavity, due to the confinement effect. Furthermore, C,N‐diphenyl imine derivatives are quantitatively encapsulated by the capsule in water and adopt an otherwise unstable cis‐form. The polyaromatic cavity suppresses the hydrolysis of the imines in water, even at elevated temperature, due to the shielding effect. Accordingly, the properties of the cis‐trans isomers could be largely altered through supramolecular manipulation. [ABSTRACT FROM AUTHOR]

Advanced encryption/decryption strategies are of great significance for information protection and data security. It is highly desirable yet quite challenging to develop functional materials for encrypting/decrypting information more effectively. Herein, a novel emissive liquid crystal elastomer (LCE) for multidimensional and multistage encryption is proposed for the first time, through synergistic utilization of phototunable fluorescence and the photoprogrammable shape. The fluorescent LCE is fabricated by incorporating an aggregation‐induced‐emission α‐cyanodiarylethene‐based hydrogen‐bonded complex and azobenzene derivative into the LCE networks through covalent bonding. Because of the photoisomerization of both these two photosensitive derivatives under the same exciting light, the consequent LCE films exhibit photoinduced reversible fluorescence changes and shape deformations that are suitable for data storage and encryption. On this basis, the collaborative usage of photolithography‐based 2D fluorescent images and photoprogramming 3D shape configurations can lead to multidimensional and multistage encryption. Moreover, this encryption strategy is reprogrammable, allowing for repeatable encoding and decrypting. The results demonstrated here reveal that the reversible phototunable fluorescent LCE materials exhibit promising applications in data storage and encryption. [ABSTRACT FROM AUTHOR]

Introduction of asymmetry into a supramolecular system via external chiral stimuli can contribute to the understanding of the intriguing homochirality found in nature. Circularly polarized light (CPL) is regarded as a chiral physical force with right‐ or left‐handedness. It can induce and modulate supramolecular chirality due to preferential interaction with one enantiomer. Herein, this review focuses on the photon‐to‐matter chirality transfer mechanisms at the supramolecular level. Thus, asymmetric photochemical reactions are reviewed, and the creation of a chiral bias upon CPL irradiation is discussed. Furthermore, the possible mechanisms for the amplification and propagation of the bias into the supramolecular level are outlined based on the nature of the photochromic building block. Representative examples, including azobenzene derivatives, polydiacetylene, bicyclic ketone, polyfluorenes, Cn‐symmetric molecules, and inorganic nanomaterials, are presented. [ABSTRACT FROM AUTHOR]

A series of azobenzene derivatives which differ in the number of rings attached to benzene is investigated using dispersion-corrected density-functional theoretical methods. The studies on the effect of extended rings on the energy of cis and trans isomers (ΔEcis–trans) of the derivatives revealed that ΔEcis–trans is increased from azobenzene to azoanthracene, however, decreased when the rings are extended in two dimensions. The time-dependent density-functional theoretical studies showed that the extension of rings in two-dimension shifts absorption maximum from ultraviolet to visible region. The investigations on fluorine and amino-substituted derivatives of azocoronene showed its cis isomer as lower in energy than trans isomer. [ABSTRACT FROM AUTHOR]

A stop-flow sample delivery system for transient spectroscopy is presented, which is, in particular, suited for laser-based instruments (quantum-cascade lasers or amplified femtosecond lasers) with excitation pulse repetition rates in the range 10–100 Hz. Two pulsing micro-valves are mounted onto a flow cuvette designed for transient IR spectroscopy, which is integrated into a flow cycle driven by a peristaltic pump. The performance of the system is demonstrated with transient IR experiments of the trans-to-cis photoisomerization of a water-soluble azobenzene derivative. The sample stands still when the micro-valves are closed and is pushed out from the probe beam focus on a 1 ms timescale when opening the micro-valves. The setup is extremely sample efficient. It needs only small sample volumes, and at the same time, it enables excitation of a large fraction of molecules in solution. [ABSTRACT FROM AUTHOR]

Photo-responsive cholesteric liquid crystals (CLCs) have attracted much attention in recent years due to their wide applications in filters, tunable optical lasers, dynamic display devices, etc. However, UV light is usually used as the external stimulus source, which is not environment-friendly enough. On the other hand, the mechanical properties of CLCs are not strong enough for these practical applications. Therefore, it still remains a challenge to endow the CLCs with visible light response and high mechanical properties at the same time. Herein, an axially chiral tetra-fluorinated binaphthyl azobenzene gelator (S-4F-AG) is synthesized. Upon 550 and 450 nm light irradiations, S-4F-AG exhibits excellent photo-switchable behaviors. Notably, the maximum content of cis-isomer and its half-life are as high as 35% and 89 h in acetonitrile, respectively. A self-supporting CLC physical gel with a storage modulus around 104 Pa can be obtained when 3wt% S-4F-AG and 12wt% binaphthyl azobenzene derivative (dopant 2) are co-doped into a nematic LC host P0616A. This CLC physical gel exhibits a temperature-driven blue, green, and red reflection colors reversibly. Importantly, such three primary RGB colors can also be realized by adjusting the exposure time of 550 nm green light. This work lays a solid foundation for the applications ranging from information storage to high-tech anticounterfeit. [ABSTRACT FROM AUTHOR]

An anionic azobenzene-appended derivative of L -ValylGlycine self-assembles into nanotubes in water. Irradiation with 365 nm light provokes trans–cis isomerization of the azobenzene unit and subsequent tube disassembly. Thermal or photoinduced (457 nm light) recovery of the trans isomer restores the nanotubes. [ABSTRACT FROM AUTHOR]

Photoswitchable molecules‐based solar thermal energy storage system (MOST) can potentially be a route to store solar energy for future use. Herein, the use of a multijunction MOST device that combines various photoswitches with different onsets of absorption to push the efficiency limit on solar energy collection and storage is explored. With a parametric model calculation, it is shown that the efficiency limit of MOST concept can be improved from 13.0% to 18.2% with a double‐junction system and to 20.5% with a triple‐junction system containing ideal, red‐shifted MOST candidates. As a proof‐of‐concept, the use of a three‐layered MOST device is experimentally demonstrated. The device uses different photoswitches including a norbornadiene derivative, a dihydroazulene derivative, and an azobenzene derivative in liquid state with different MOSTproperties, to increase the energy capture and storage behavior. This conceptional device introduces a new way of thinking and designing optimal molecular candidates for MOST, as much improvement can be made by tailoring molecules to efficiently store solar energy at specific wavelengths. [ABSTRACT FROM AUTHOR]

Azobenzene/cyclodextrin (CD) host‐guest complexes can dissociate and reform under light irradiation because of photoisomerization of azobenzene. Azobenzene/CD host‐guest interactions have been used to construct photo‐controlled supramolecular systems. However, typical azobenzene/CD host‐guest interactions are controlled using UV light that may damage organic and biological components. To broaden the applications of this type of supramolecular construct, visible‐light‐responsive azobenzene/CD host‐guest interactions have received growing attention in recent years. In this Concept, the host‐guest interactions of visible‐light‐responsive azobenzene derivatives with CDs and their applications are reviewed. In particular, the advantages of visible‐light‐responsive azobenzene/CD systems for biomedical applications and surface functionalization are discussed, such as photo‐controlled release, photoswitchable surfaces, and orthogonal supramolecular micropatterned surfaces. Challenges and perspectives for the field are summarized and discussed. [ABSTRACT FROM AUTHOR]

A series of compact azobenzene derivatives were investigated as phase-transition molecular solar thermal energy storage compounds that exhibit maximum energy storage densities around 300 J g−1. The relative size and polarity of the functional groups on azobenzene were manifested to significantly influence the phase of isomers and their energy storage capacity. [ABSTRACT FROM AUTHOR]

[Display omitted] • H-daa, F-daa, Cl-daa and Br-daa were calculated on b3lyp/g/def2-tzvp. • The transition states of H-TS-daa, F-TS-daa, C-TSl-daa and Br-TS-daa were found in the ground state. • The PESs of H-daa, F-daa, Cl-daa and Br-daa were calculated in S 0 , S 1 and S 2 , respectively. • The isomerization mechanisms are different in the ground state and excited state. This article investigates the geometric structure and isomerization mechanism of 4,4-acetamidazobenzene molecules with halogen atoms (F, Cl, Br) substituted at four ortho positions through density functional theory (DFT) calculations. The calculation method was b3lyp/g, and the base set was def2-tzvp. According to DFT calculations, the ortho substitution of the halogen atoms differently distorted the molecular plane of the trans isomers, resulting in obvious absorption peaks in the visible range, giving them visible-light driven properties. In addition, the transition state (TS) of the cis–trans isomerization reaction in the ground state was also found. To study the molecular isomerization mechanism, the potential energy surfaces (PESs) of the ground state (S 0), first excited state (S 1), and second excited state (S 2) of halogen substituted azobenzene derivatives were scanned separately. Through the potential energy surface curve of the ground state, the mechanism of isomerization reaction in the ground state of the four molecules is realized through a rotation-assisted inversion pathway, which is consistent with the calculation of TS. When the molecules are in the excited states, the isomerization pathways are realized through rotation pathways. [ABSTRACT FROM AUTHOR]

Yuki Nagai is an Assistant Professor in the Department of Applied Chemistry at Ritsumeikan University in Japan. He recently published his first article as a submitting corresponding author in Angewandte Chemie, focusing on a nonlinear photochromic reaction. Nagai's research interests include photochromic materials, photofunctional materials, stimuli-responsive materials, and self-assembly. He values the ability to see changes and differences with the naked eye in his research and hopes to inspire curiosity in others through his work. Nagai also enjoys reading comics and visiting museums in his free time. [Extracted from the article]

Yuki Nagai is an Assistant Professor in the Department of Applied Chemistry at Ritsumeikan University in Japan. He recently published his first article as a submitting corresponding author in Angewandte Chemie. His research focuses on photochromic materials, photofunctional materials, stimuli-responsive materials, and self-assembly. Nagai finds conducting research to be an expression of who he is and enjoys being able to see changes and differences with the naked eye. He hopes that his work will inspire curiosity in others and aims to establish research that others will want to imitate. [Extracted from the article]

The mitotic kinesin Eg5 is a plus-end directed homotetrameric molecular motor essential for the formation of bipolar spindles during cell division. Kinesin Eg5 is overexpressed in cancer cells and hence considered as a target for cancer therapy; the inhibitors specific for Eg5 have been developed as anticancer drugs. In this study, we synthesized a novel functional photoresponsive inhibitor composed of spiropyran and azobenzene derivatives to control Eg5 function with multistage inhibitory activity accompanied by the formation of different isomerization states. The photochromic inhibitor spiropyran-sulfo-azobenzene (SPSAB) exhibited three isomerization states: spiro (SP)- trans , merocyanine (MC)- cis and MC- trans , upon exposure to visible light, ultraviolet and in the dark, respectively. SPSAB-induced reversible changes in the inhibitory activity of ATPase and motor activities correlating with photoisomerization among the three states. Among the three isomerization states of SPSAB, the SP- trans isomer showed potent inhibitory activity at an IC50 value of 30 µM in the basal ATPase assay. MC- trans and MC- cis exhibited less inhibitory activity at IC50 values of 38 and 86 µM, respectively. The results demonstrated that the novel photochromic inhibitor enabled precise control of Eg5 function at three different levels using light irradiation. [ABSTRACT FROM AUTHOR]

New photosensitive polymeric film composites based on oligo-N-glycidylcarbazole oligomer with azobenzene dyes as additives (azobenzene derivatives with a glycidyl group in their structure) were obtained and investigated. It was shown that the created composites exhibit photovoltaic properties when they are irradiated in the absorption region of the azobenzene dye. The mechanism and the photovoltaic effect in the investigated composites are discussed. [ABSTRACT FROM AUTHOR]

The photomechanical effect has been studied so far mainly in elastomers, but recently more and more publications, in which this effect is studied for other materials too, so-called glassy or amorphous polymers (in particular polyimides), have appeared. This mini-review describes the photomechanical effect in polyimides containing light-sensitive derivatives of azobenzene and, in some cases, for comparison, in polyamides and polystyrenes. The work aims to present the influence of chemical structure factors on the bending angle of free-standing polymer films and their long-term stability. We focused on aspects of polymer structure such as the content of azo-moieties, the flexibility of the backbone, kind of azobenzene attachment (covalent/non-covalent), degree of crystallinity, influence the intermolecular H-bonds. The paper should help in designing new amorphous azopolymers with properties tailored to specific applications. [ABSTRACT FROM AUTHOR]

Azobenzenes are among the most extensively used molecular switches for many different applications. The need to tailor them to the required task often requires further functionalization. Cross-coupling reactions are ideally suited for late-stage modifications. This review provides an overview of recent developments in the modification of azobenzene and its derivatives by cross-coupling reactions. 1 Introduction 2 Azobenzenes as Formally Electrophilic Components 2.1 Palladium Catalysis 2.2 Nickel Catalysis 2.3 Copper Catalysis 2.4 Cobalt Catalysis 3 Azobenzenes as Formally Nucleophilic Components 3.1 Palladium Catalysis 3.2 Copper Catalysis 3.3 C–H Activation Reactions 4 Azobenzenes as Ligands in Catalysts 5 Diazocines 5.1 Synthesis 5.2 Cross-Coupling Reactions 6 Conclusion [ABSTRACT FROM AUTHOR]

Photo-responsive mechanical actuator is a class of stimuli-responsive materials transferring light to mechanical energy through macroscopic transformation. To fabricate photo-responsive mechanical actuator, soft polymeric materials crosslinked with functional bridging structures are desired. Supramolecular interaction is a relatively common way to fabricate crosslinked materials due to its excellent self-assembly performance. And azobenzene and derivatives are ideal candidates of photo-responsive materials because of the unique photo-induced trans-cis isomerization. Here, a new kind of crosslinked materials based on supramolecular interaction between 4,4′-dihydroxyazobenzene and chitosan is reported. Under 355 nm irradiation, the macroscopic bending of polymeric materials occurs rapidly due to the photo-isomerization of 4,4′-dihydroxyazobenzene. Meanwhile, the photo-responsive mechanical actuator can also lift weight which is up to 200 times that of the actuator itself, and convert energy from light to mechanical work efficiently. This report suggests a new kind of photo-responsive actuator based on supramolecular interaction and may be helpful to contribute a theoretical basis to the design and synthesis of photo-responsive mechanical actuator suitable for large-scale manufacturing industrialization in future. [ABSTRACT FROM AUTHOR]

Multicomponent supramolecular assembly systems enable the generation of materials with outstanding properties, not obtained from single‐component systems, via a synergetic effect. Herein, we demonstrate a novel supramolecular coassembly system rendering highly ordered quantum dot (QD) arrangement structures formed via the self‐assembly of azobenzene derivatives, where the photocontrollable photoluminescence (PL) properties of the QDs are realized based on photoisomerization. Upon mixing the assembled azobenzene derivatives and QDs in apolar media, a time‐evolution coaggregation into hierarchical nanosheets with a highly ordered QD arrangement structure occurs. Upon photoirradiation, the nanosheets transform into ill‐defined aggregates without arranged QDs together with enhancing the PL intensity. In days, the photoirradiated coaggregates undergo recovery of the PL properties corresponding to the arranged QDs through thermal isomerization. [ABSTRACT FROM AUTHOR]

Azobenzene and its derivatives are one of the most widespread molecular scaffolds used in a range of modern applications, as well as in fundamental research. After photoexcitation, azo‐based photoswitches revert back to the most stable isomer on a timescale (t1/2) that determines the range of potential applications. Attempts to bring t1/2 to extreme values prompted the development of azobenzene and azoheteroarene derivatives that either rebalance the E‐ and Z‐isomer stabilities, or exploit unconventional thermal isomerization mechanisms. In the former case, one successful strategy has been the creation of macrocycle strain, which tends to impact the E/Z stability asymmetrically, and thus significantly modifyt1/2. On the bright side, bridged derivatives have shown an improved optical switching owing to the higher quantum yields and absence of degradation. However, in most (if not all) cases, bridged derivatives display a reversed thermal stability (more stable Z‐isomer), and smaller t1/2 than the acyclic counterparts, which restricts their potential interest to applications requiring a fast forward and backwards switch. In this paper, the impact of alkyl bridges on the thermal stability of phenyl‐azoheteroarenes is investigated by using computational methods, and it is revealed that it is indeed possible to combine such improved photoswitching characteristics while preserving the regular thermal stability (more stable E‐isomer), and increased t1/2 values under the appropriate connectivity and bridge length. [ABSTRACT FROM AUTHOR]

Azobenzene and its derivatives are proposed as promising solar thermal fuel (STF) candidates due to the unique photoinduced trans–cis isomerization. However, the routinely processed azobenzene/inorganic–nonmetal nanocomposite‐based STF usually encounters the problems of close‐packed structure and the poor penetration of UV light, which need a solvent pretreatment charging process before STF application. Electrochemical deposition (ED) is widely used in the preparation of photoelectric functional devices because of its unique polymerization and deposition process. Here, an azobenzene‐based cross‐linking film is successfully prepared from a new functionalized azobenzene derivative, BCz‐BO‐Azo, by ED approach to develop a ready‐to‐use STF film without any pretreatments. The energy density of BCz‐BO‐Azo is 101 J g−1, and the energy storage half‐life of BCz‐BO‐Azo ED film is extended by 750% compared with that of pristine BCz‐BO‐Azo solid. The charged BCz‐BO‐Azo ED film also can release thermal energy to heat up itself quickly under a certain external stimulus. Due to the fast charging process, long energy storage half‐life, and quick stimulated release of the BCz‐BO‐Azo ED film, this kind of ready‐to‐use STF has distinct superiority in daily use, such as self‐defrosting glasses, building wall insulation, and solar energy transport. [ABSTRACT FROM AUTHOR]

Light‐induced transitions between the trans and cis isomer of triazatriangulenium‐based azobenzene derivatives on Au(111) surfaces were observed directly by scanning tunneling microscopy, allowing atomic‐scale studies of the photoisomerization kinetics. Although the azobenzene units in these adlayers are free‐standing and spaced at uniform distances of 1.26 nm, their photoswitching depends on the isomeric state of the surrounding molecules and, specifically, is accelerated by neighboring cis isomers. These collective effects are supported by ab initio calculations indicating that the electronic excitation preferably localizes on the n–π* state of trans isomers with neighboring cis azobenzenes. [ABSTRACT FROM AUTHOR]

Conjugate Sn(IV)(pyropheophorbide a)dichloride–(peptide nucleic acid) catalyzes reduction of azobenzene derivatives in the presence of complementary nucleic acid (NA) upon irridiation with red light (660 nm). This is the first red light-induced NA-templated photoreduction. It is highly sensitive to single mismatches in the NA-template and can detect down to 5 nM NAs. [ABSTRACT FROM AUTHOR]

In this study, novel photo‐stimulated molecularly imprinted polymers based on magnetic mesoporous carrier surface were developed for selective identification and intelligent separation of sulfamerazine in complex samples. The photosensitive monomer of the molecularly imprinted polymers was azobenzene derivative 5‐[(4‐(methacryloyloxy)phenyl) diazenyl] isophthalic acid with stimulus reaction mechanisms, which has photoisomerization between trans and cis for N=N bonds. Further, the properties of the photo‐stimulated molecularly imprinted polymers were further evaluated through several sets of adsorption experiments. It illustrated that the maximum adsorption amount is 0.45 mmol/L. By ultraviolet spectrophotometry, the material reaches typical characteristic peaks of photo sensitivity, and the cycle time is 16 min. Three adsorption and desorption processes were repeated, the adsorption rate reached 34.4%. Overall, the photo‐stimulated molecularly imprinted polymers can enrich and separate determine sulfamerazine with high selectivity, which have good recovery for real samples. [ABSTRACT FROM AUTHOR]

An azobenzene derivative containing a dimethylchlorosilane end group was chemically attached to a flexible polymer substrate to create permanent photo alignment layer. The commercially obtained polymer substrate (overhead projector film) was characterised and found to contain cellulose acetate as the main component. Surface functionalization of the substrate was confirmed through X-ray photoelectron spectroscopy (XPS), attenuated total reflectance fourier transform infrared (ATR-FTIR) spectroscopy, water contact angle (CA) and atomic force microscopy (AFM) techniques. Photo-isomerisation behaviour of the azo-layer on the polymer substrate was additionally confirmed by UV-diffuse reflection spectroscopy (UV-DRS). Further, the azo-modified flexible substrate was analysed for the orientation of the bulk liquid crystal (LC) sample and tuning the LC orientation by utilising photo-switching behaviour of the azo-layer on the substrate. [ABSTRACT FROM AUTHOR]

Study the synthesis and fluorescent properties of a new series of D‐π‐A fluorescent dyes based on nicotinonitrile and azobenzene is the main objective for this work. Reduction with Zn/HCl, diazotization with HCl/NaNO2, and coupling using catalytic NaOH or AcONa are simple applied methods. Where, nicotinonitrile 3 was synthesized via reduction of nitro derivative 1 followed by diazotization with HCl/NaNO2 in acetic acid. The formed benzene diazonium chloride was coupled with several activated phenols, aniline, and α‐CH acids to yield the respective azo dyes 4‐11 in moderate to good yield. Dyes 11a‐d subjected to intermolecular cyclization with hydrazine hydrate resulted in pyrazole dyes 12‐15 in moderate yield. Dyes containing pyrazole moiety or electron‐withdrawing groups at the sixth position of pyridine nucleus exhibit stronger blue‐green emission (λfl.max = 503, 507, 500, 501, 502, 493, and 514 nm) than that of the rest of compounds. [ABSTRACT FROM AUTHOR]

Azobenzene derivatives have fast light response characteristics; in this paper, a new azobenzene derivative (Azo) was synthesized and to be made a composite (PANI/GO/Azo) with polyaniline/graphene oxide (PANI/GO). Both composites were carefully investigated by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), and thermogravimetric analysis (TGA). Moreover, their electrochemical properties were characterized by the electrochemical workstation, including cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), cycling stability, and electrochemical impedance spectroscopy (EIS). The results demonstrated that the PANI/GO/Azo composite has a higher capacitance of 478.3 F g−1 than that of PANI/GO (359.9 F g−1) at a current density of 1 A g−1. PANI/GO/Azo composite showed excellent photosensitive electrochemical properties under UV irradiation, and its rate of capacitance change achieved about 52.57%. Additionally, the PANI/GO/Azo composite also displayed high reversibility, with specific capacitance retention of 92% after 500 cycles. Therefore, the PANI/GO/Azo electrode with a controllable electrochemical performance by UV irradiation had a great potential in the photoresponsive supercapacitor. [ABSTRACT FROM AUTHOR]

The trans-azobenzene (AB) substituted derivatives with bulky carbazole (1), phenothiazine (2), and phenyl (3) have been synthesized to understand the effect of steric crowding around the –N＝N– linkage on the photoisomerization process. The substituents maintain orthogonality to the azobenzene plane and the electronic properties exhibit a combination of individual chromophores. Irradiation of 1 and 2 with various light sources including a 365 nm pen-ray lamp, and a 150 W Xe–Hg lamp, and even exposure to sunlight for a week does not yield the cis isomer revealing the exceptional photostability of the synthesized azobenzene derivatives. These studies suggest that possessing steric crowding around the azo linkage would be a potential strategy to develop photostable azobenzene-based functional materials. [ABSTRACT FROM AUTHOR]

The structure and thermal properties of azobenzene derivatives R1–C6H4–N=N–C6H4–R2, where R1/R2 = CH3COO/C2H5O (I), CH2=C(CH3)COO/C2H5 (II), or C6H13COO/C2H5O (III), were studied by differential scanning calorimetry and X-ray diffraction. Compounds I and III form a mesophase (nematic) upon melting, whereas compound II does not produce a mesophase. Compound III is characterized by two high-temperature crystal–crystal phase transitions IIIIII–IIIII–IIII. The low-temperature crystal modification, which is not a precursor of the mesophase, was structurally characterized. The crystal packing of I is stabilized by C−H···π interactions and consists of alternating loosely and closely packed regions. Weak directional interactions that connect the molecules into zigzag chains ensure the structuring of the mesophase of I. The possible structuring pattern of the mesophase of III is discussed. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this paper is to synthesize some new azobenzene dyestuffs clubbed with thiazolidinone moiety and their solicitation in dyeing polyester fabrics representing their antibacterial evaluation. Design/methodology/approach: Herein, the authors report the synthesis of new thiazolidinone moiety after the coupling of diazotized 4-aminoacetophenone with resorcinol. The newly synthesized dyes were characterized by IR, elemental analysis, mass spectroscopy and proton nuclear magnetic resonance (1H NMR) spectral studies. The characteristics of dyeing of these dyestuffs were evaluated at optimum conditions. Concurrent with dyeing of polyester fabric for synthesized dyes with their antibacterial activity was estimated. Antimicrobial activity of the dyed fabrics at different concentrations was evaluated against gram-positive and gram-negative bacteria. Findings: Synthesized azobenzene dyestuffs clubbed with thiazolidinone dyes were applied on polyester fabrics. It was remarked that the modified dyes exhibited better colourfastness properties. Furthermore, the synthesized dyes revealed antimicrobial activity against gram-positive and gram-negative bacteria. Research limitations/implications: The synthesized azobenzene dyes for polyester dyeing were not bore earlier. Practical implications: The azobenzene dyes were accountable for giving improved colourfastness properties on polyester fabrics. Social implications: The synthesized azobenzene derivatives are sensibly expensive and applicable dyes accompanied with good antimicrobial and anticancer activities. Originality/value: A common process could be affording textiles of colour and antibacterial assets. The newly synthesized dyes containing thiazolidinone moieties with azobenzene coupler showed interesting disperse colourant for polyester with good antibacterial activity. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Photoswitchable organic molecules can undergo reversible structural changes with an external light stimulus. These optically controlled molecules have been used in the development of "smart" polymers, optical writing of grating films, and even controllable in vivo drug release. Being the simplest class of photoswitches in terms of structure, azobenzenes have become the most ubiquitous, well-characterized, and implemented organic molecular switches. Given their predictable response, they are ideally suited to create an all-optically controlled switch. However, fabricating a monolithic optical device comprised solely of azobenzene while maintaining the photoswitching functionality is challenging. In this work, we combine integrated photonics with optically switchable organic molecules to create an optically controlled integrated device. A silica toroidal resonant cavity is functionalized with a monolayer of an azobenzene derivative. After functionalization, the loaded cavity Q is above 105. When 450 nm light is coupled into cavity resonance, the azobenzene isomerizes from trans isomer to cis isomer, inducing a refractive index change. Because the resonant wavelength of the cavity is governed by the index, the resonant wavelength changes in parallel. At a probe wavelength of 1300 nm, the wavelength shift is determined by the duration and intensity of the 450 nm light and the density of azobenzene functional groups on the device surface, providing multiple control mechanisms. Using this photoswitchable device, resonance frequency tuning as far as 60% of the cavity's free spectral range in the near-IR is demonstrated. The kinetics of the tuning are in agreement with spectroscopic and ellipsometry measurements coupled with finite element method calculations. [ABSTRACT FROM AUTHOR]

[Display omitted] • Four azobenzene-derivatives were reported for endogenous carbon monoxide imaging. • The optimal probe showed efficient fluorescence quenching in the presence of Cu2+. • The quenched emission could be recovered by CO within 180 s. • A static sensing mechanism by forming a non-fluorescent complex with Cu2+ was proved. Detection of endogenous CO (carbon monoxide) is an interesting topic in biology because it has been discovered as a messenger for signal transduction and therapeutic effects in vital biological activities. Fluorescence imaging has proven a powerful tool for detecting endogenous CO, which drives the development of low-cost and easy-to-use fluorescent probes. In this study, four azobenzene derivatives (A1, A2, A3, and A4) with various substituents were reported, including their geometric structures, photophysical parameters, and spectral responses to Cu2+ and CO. The relationship between substituent structure and performance was discussed along with Cu2+ quenching and CO sensing mechanisms. The optimal probe (A1), which had no substituent, efficiently quenched fluorescence in the presence of Cu2+, with its PLQY decreased from 0.33 to 0.02, PLQY = photoluminescence quantum yield. Upon CO deoxidization, A1′s fluorescence could be recovered (PLQY recovered to 0.32) within 180 s. Its sensing mechanism was static by forming a non-fluorescent complex with Cu2+ (with a stoichiometric ratio of 1:1). The bioimaging performance of A1 for endogenous CO in HeLa cells was reported. [ABSTRACT FROM AUTHOR]

[Display omitted] • Colloidal PMMA nanoparticles were prepared by emulsifier-free emulsion polymerization. • Acidochromic colloids were prepared by doping azobenzene with different auxochromes. • The azobenzene-containing nanoparticles were used as eco-friendly inks. • Exposure to acidic HCl vapor resulted in different coloration of the inks. • The colors were decayed with time and also after exposure to triethylamine vapor. N,N -dihydroxyethyl azobenzene compounds with different functional groups of hydrogen, electron-donating hydroxyl (OH), and electron-withdrawing nitro (NO 2) were synthesized by a two-step diazotization and coupling method. Colloidal poly(methyl methacrylate) (PMMA) nanoparticles, prepared by emulsifier-free emulsion polymerization, were doped with 3 wt% of the three azobenzenes to prepare acidochromic colloids. Acidochromic properties of all the azobenzenes and the polymer colloids were investigated in acidic buffers. Azobenzene compounds doped on polymer particles showed different colors in buffers with different pH values due to the presence of different functional groups, which makes them highly applicable as acid detectors. The electron-withdrawing NO 2 functional group caused a small bathochromic shift in the azobenzene spectrum, and the azobenzene containing OH functional group showed higher bathochromic shift than the unsubstituted azobenzene. The colloidal PMMA nanoparticles doped with the three azobenzene compounds were used as eco-friendly inks for stamping and hand-signing on cellulosic papers. Exposure to acidic HCl vapor resulted in different coloration of the printed marks due to the protonation of the azobenzenes. These colors of the protonated forms were decayed with time and also after exposure to triethylamine vapor. The stamped patterns showed a high fatigue and no change in color intensity up to 20 cycles. This shows that these polymeric inks can be used as anticounterfeiting inks for security-marking of confidential documents and banknotes. The developed inks showed time-dependent characteristics and responsivity to acid and base vapors, which make them highly applicable in security marking of confidential documents and also detection of acid and base. [ABSTRACT FROM AUTHOR]

The reversible photoisomerization of azobenzenes has been extensively studied to construct systems with optical responsiveness; however, this process limits the luminescence of these compounds. Recently, there have been many efforts to design and synthesize fluorescent azobenzene compounds, such as inhibition of electron transfer, inducing aggregation, and metal-enhancement, which make the materials ideal for application in fluorescence probes, light-emitting devices, molecular detection, etc. Herein, we review the recently reported progress in the development of various fluorescent azobenzenes and summarize the possible mechanism of their fluorescence emission. The potential applications of these materials are also discussed. Finally, in order to guide research in this field, the existing problems and future development prospects are discussed.

A new di-2-pyridylamine ligand with an appended azobenzene group (2-C5H4N)2N-4-C6H4-N＝N-Ph, dpaa, is reported. This ligand readily forms the platinum(II) complexes [PtMe2(dpaa)], 1, and [PtCl2(dpaa)], 2. Complex 1 is electron-rich and it undergoes oxidative addition with I2, MeI or PhCH2Br to give the corresponding organoplatinum(IV) complexes [PtI2Me2(dpaa)], [PtIMe3(dpaa)] or [PtBrMe2(CH2Ph)(dpaa)]. Both the ligand dpaa and its platinum complexes undergo photoswitching by trans–cis isomerization about the N＝N linkage. [ABSTRACT FROM AUTHOR]

A triphenylamine derivative decorated with an azobenzene group (TDA) was synthesized via a SuFEx click reaction and its polymer, poly(triphenylamine) (PTDA), was polymerized through a redox polymerization. More interestingly, its polymeric metal complex, PTDA‐Fe, can be simply obtained via one‐pot reaction between TDA and FeCl3 owing to TDA showing a strong affinity to the FeIII ion. The sandwich memory device based on PTDA nanofilms as active layers exhibited a binary memory performance. However, the memory device based on its polymeric metal complex exhibited a unique ternary memory behavior. The different memory performances should come from the different conductive mechanism. The mechanism of such ternary memory devices is illustrated based on both the theoretical calculation and experiments. Our work provides new insights into the preparation of novel materials for multilevel memory devices. [ABSTRACT FROM AUTHOR]

A single‐molecule method has been developed based on the scanning tunneling microscope (STM) to selectively couple a series of aniline derivatives and create azobenzenes. The Au‐catalyzed oxidative coupling is driven by the local electrochemical potential at the nanostructured Au STM tip. The products are detected in situ by measuring the conductance and molecular junction elongation and compared with analogous measurements of the expected azobenzene derivatives prepared ex situ. This single‐molecule approach is robust, and it can quickly and reproducibly create reactions for a variety of anilines. We further demonstrate the selective synthesis of geometric isomers and the assembly of complex molecular architectures by sequential coupling of complementary anilines, demonstrating unprecedented control over bond formation at the nanoscale. [ABSTRACT FROM AUTHOR]