Amphiphilic Azobenzene Derivative Research Articles

An amphiphilic azobenzene derivative as a crosslinker in the construction of smart supramacromolecular hydrogels

The reversible photoisomerization of azobenzene (Azo) has been utilized to construct supramacromolecular hydrogels (SMHGs) in which the structure can be controlled by light. However, most of these examples have been realized only through grafting Azo functional group onto the macromolecular chains, and low-molecular-weight Azo derivatives are relatively scarce. Here, a novel amphiphilic azobenzene derivative (APA) has been designed and synthesized, which can be used as a low-molecular-weight crosslinker to construct SMHGs via host-guest interactions between Azo and β-cyclodextrin (β-CD). APA, with two hydrophobic ends and a hydrophilic segment, can self-assemble to spherical particles in the mixed solvent of THF and H2O, and disassemble upon UV light irradiation. When APA is mixed with the solution of hyaluronic acid modified by β-CD (HA-CD), hydrogels can form at different mass fractions of HA-CD. Moreover, when the molar ratio of APA and β-CD is 0.5, the resultant hydrogel has the highest G' value. Benefiting from the host-guest interactions between Azo and β-CD, as well as the intermolecular hydrogen bonds of hyaluronic acid, hydrogels undergo both photo- and thermo-responsive sol-gel transition. The release of Rhodamine B from the hydrogel, could be controlled by UV light irradiation or high temperature. The work presented here demonstrates a simple strategy to construct photo-responsive SMHGs by Azo-derived low-molecular-weight crosslinkers.

Photoreversible formation of nanotubes in water from an amphiphilic azobenzene derivative.

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.

Molecular organization and optical switching of liquid-crystalline azobenzenes in monomolecular films

The photoisomerization and thermal relaxation processes of three amphiphilic azobenzene derivatives (LCAn) showing liquid-crystalline properties were studied in solutions and in monomolecular films formed using Langmuir and Langmuir-Blodgett techniques. The well-controlled isomeric state of LCAn in chloroform during the UV irradiation allowed to prepare spreading solutions containing trans isomers, cis isomers or their mixture and to investigate molecular organization in the Langmuir films made of them. Surface pressure-mean molecular area isotherms and compression modulus-surface pressure dependences delivered information on a thermodynamic state, phase transitions and intermolecular interaction in the monolayers. LCAn in the trans state create densely-packed films, in which the photoisomerization do not occur due to the lack of free volume for the change of the molecules conformation and their strong tendency for the H-type aggregation. However, the reversible switching of the LCAn conformation during cyclic photoisomerization and thermal relaxation processes was observed in the LB films initially deposited onto quartz substrates in the cis state, where molecules are loosely-packed and exist in the monomeric form. Kinetics and rate constants of the photoisomerization and thermal relaxation were determined based on the recorded absorption spectra in order to obtain information on their efficiency and on the impact of the replacement of the alkyl chain attached in the LCAn para position with the alkyloxy chain. Our research show that LCAn are promising materials for application in optical memories, logic gates and holographic gratings.

Tunable morphology and surface wettability of an amphiphilic azobenzene derivative and its melamine-induced self-assembly

Herein, a series of novel hydrogen-bonded complexes derived from 4-[[(dodecyloxy)benz-4-yl]azo]benzoic acid (DBA) and melamine are reported. The morphology and surface wettability of the resulting self-assembled supramolecular architectures can be easily modulated not only by varying the molar ratios of DBA and melamine, but also by external UV irradiation. Based on the results of atomic force microscope, X-ray diffractometer and contact angle measurements, orientation of the coassembled units with different molar ratios of DBA and melamine could be clearly confirmed. Moreover, the effect of photo-isomerisation of the azobenzene units on the wettability of the assemblies has been investigated in detail. As we know, the films derived from the cis-azobenzene derivative usually exhibit a more hydrophilic property than that from the trans-azobenzene derivative. However, the opposite results were obtained for the samples derived from the cis isomers of DBA–melamine (3:1) complexes or DBA. An explanation, based on the surfaces topography, has been proposed.

Photoresponsive switches at surfaces based on supramolecular functionalization with azobenzene-oligoglycerol conjugates.

The synthesis, supramolecular complexation, and switching of new bifunctional azobenzene-oligoglycerol conjugates in different environments is reported. Through the formation of host-guest complexes with surface immobilized β-cyclodextrin receptors, the bifunctional switches were coupled to gold surfaces. The isomerization of the amphiphilic azobenzene derivatives was examined in solution, on gold nanoparticles, and on planar gold surfaces. The wettability of functionalized gold surfaces can be reversibly switched under light-illumination with two different wavelengths. Besides the photoisomerization processes and concomitant effects on functionality, the thermal cis to trans isomerization of the conjugates and their complexes was monitored. Thermal half-lives of the cis isomers were calculated for different environments. Surprisingly, the half-lives on gold nanoparticles were significantly smaller compared to planar gold surfaces.

Photoisomerization of amphiphilic azobenzene derivatives in Langmuir Blodgett films prepared as polyion complexes, using ionic polymers

Polyion complexation in mixed Langmuir and Langmuir Blodgett (LB) films of photochromic amphiphilic azobenzene carboxylic acids, 11-[4-(4-hexylphenyl)azo] phenoxyundecanoic acid, 11-(4-phenylazo)phenoxyundecanoic acid, and diamine grafted poly(methylmethaacrylate) polymers has been studied. Monolayer behaviour of the pure components and mixed films was studied through pressure–area isotherms and LB films were characterized by spectroscopic, X-ray diffraction and Atomic force microscopy techniques. Aggregation (H-type), often observed in LB films of pure amphiphilic azo acids, was partly avoided in the mixed LB films as indicated by absorption spectral studies. Photoisomerization of the polyion complexed LB films was also studied. The results altogether demonstrate that amine grafted polymer enter into a polyion complexation with azo acid carboxylate group. LB films could be obtained by transfer of the composite monolayers and these LB films exhibited different levels of aggregation of the azo acids. Reversible photoisomerization was observed in LB films with unaggregated azo acid.

Collective Molecular Precession Induced by Rotating Illumination in Photosensitive Langmuir Monolayers

Langmuir monolayers of an amphiphilic azobenzene derivative exhibit easily perturbable mesophases with long-range orientational order that couples strongly to linearly polarized light, resulting in symmetric photoaligned textures. Controlled rotation of the polarization plane induces continuous collective precession of the molecular field, which reveals the shear-thinning nature of the surface rotational viscosity. The dynamics is controlled by a balance between the strength of the optical coupling and viscous dissipation so that an increase in the rotational velocity results in a dampening of the synchronous anharmonic oscillations of the orientational field, as revealed by a space-time analysis of the Brewster angle microscopy images.

Photonic manipulation of topological defects in liquid-crystal emulsions doped with azobenzene derivatives

By modulating liquid-crystal alignment on a colloidal sphere, we successfully manipulated topological defects in glycerol-droplet/liquid-crystal emulsions doped with amphiphilic azobenzene derivatives. At an initial state, a disclination loop (Saturn ring) could be observed around the droplet, in which the azobenzene molecules should adsorb onto the droplet and liquid crystal molecules align normally to the surface of the droplet. On irradiation with ultra-violet light ( λ = 365 nm), the disclination loop was unfastened and transformed into two point defects called boojums. This should be attributed to the alignment change of the liquid crystal molecules from normal to planar arrangement triggered by trans-to- cis photoisomerization of the adsorbed azo-dyes. On irradiation with visible light causing cis-to- trans photoisomerization ( λ = 435 nm), the boojums went back to the Saturn ring reversibly.

UNPOLAR AND POLAR HOLOGRAPHIC GRATING RECORDING BY CIRCULARLY POLARIZED LIGHT ON PHOTOANISOTROPIC AZOBENZENE LANGMUIR–BLODGETT FILMS

A comparative study of photo-induced optical anisotropy was carried out on Langmuir–Blodgett films prepared from five different amphiphilic azobenzene derivatives. The anisotropy was induced by a linearly polarized pump beam of an Ar-ion laser at λ=514 nm and monitored by a linearly polarized probe beam of a He–Ne laser at λ=633 nm . Large optical anisotropy up to 0.35 has been induced. Holographic gratings were recorded by two left circularly polarized beams of the Ar-ion laser and time evolution of the first-order diffraction efficiency of the probe beam was recorded in an automatic regime. In such a geometry, the spatial modulation of refraction index reaches 0.14. The experimental data is consistent with a model for a photo-induced collective chromophore realignment in the heterogeneous domain structure of the films studied. The influence of an electric field of the corona discharge on the grating recording process was also studied and polar diffraction gratings have been prepared by a spatially periodic photo-poling process.

Organization of an Amphiphilic Azobenzene Derivative in Monolayers at the Air−Water Interface

The organization of an amphiphilic azobenzene derivative, 4-octyl-4‘-(5-carboxy- pentamethyleneoxy) azobenzene (8A5), in monolayers at the air−water interface is strongly controlled by association phenomena due to intermolecular interactions of the azobenzene moiety. The monolayer behavior has been investigated by measuring surface pressure−area and surface potential-area isotherms as well as by Brewster angle microscopy (BAM) and reflection spectroscopy. In particular, dimers are formed that reorient from a flat or slightly tilted orientation to an orientation nearly normal to the water surface and forming H-aggregates upon monolayer compression. The BAM images clearly show domains with long range tilt orientational order. The observed shifts of the reflection maximum as well as the intensities of the band are accounted for by a model of molecular association and reorientation. The intermolecular interactions are strongly modified by variation of the subphase pH controlling the dissociation of the hydrop...

Electrostatically Induced Isomerization of Azobenzene Derivatives in Langmuir−Blodgett Films

A novel electrochemically induced cis-to-trans isomerization process involving amphiphilic azobenzene derivatives in Langmuir−Blodgett monolayer films at electrode/electrolyte interfaces was examined using electrochemical and UV−visible absorption measurements. This isomerization proceeds electrostatically, i.e., with no Faradaic current and no discernible features in the double-layer capacitive charging current, when relatively positive electrode potentials are applied to the monolayer film. This electrostatically induced process is rather slow (first-order rate constants in the 10-2−10-1 s-1 range over the potential range of +0.65 to +0.85 V vs Ag/AgCl, respectively), but the highest rate constant measured (at +0.85 V vs Ag/AgCl) represents an increase of approximately 3 orders of magnitude compared to that of the thermal isomerization process. Surprisingly, the activation energy for the electrostatic process was found to be essentially potential independent and nearly the same as that for thermal isome...

Photochemical regulation of ion transport through “quasi-channels” embedded in black lipid membrane

The black lipid membranes (BLM) of soybean lecithin doped with an amphiphilic azobenzene derivative, 4-octyl-4′-(5-carboxypentamethyleneoxy) azobenzene (8A5), was fabricated, and the K + ion permeation through the “quasi-channels”, as represented by the steady d.c. current signal across the membrane, was photochemically regulated. A transient photocurrent overlapping with the steady d.c. current due to photoisomerization of 8A5 was observed in the BLM cell filled with a diluted KCl solution for the first time. Dependence of the steady photocurrent on the molar concentration ratio of 8 A5 to lecithin, [8 A5] / [lecithin], was also examined. It has been found that the normalized conductivity change, δG/G(trans), is roughly proportional to the square of [8A5]/[lecithin]. The result would suggest that one “quasichannel” consists of two 8A5 molecules.

Conformational fluctuation and ion permeation of lipid bilayers doped with azobenzene derivative: Infrared spectroscopic study

AbstractWe have fabricated the liposome dispersions of L‐α‐dimyristoylphosphatidylcholine (DMPC) doped with an amphiphilic azobenzene derivative, 4‐octyl‐4'‐(5‐carboxypentamethyleneoxy)azobenzene (8A5). The conformation of the DMPC liposome membrane was changed reversibly according as photoisomerization of 8A5. Fourier transform infrared spectroscopy (FTIR) was applied to study interactions between dopants and host lipids. Dependence of FTIR spectra of the CH2 stretching bands on the molar ratio of 8A5 and on temperature indicates that 8A5 molecules induce a large fluctuation on the molecular packing of the membrane around the phase transition temperature. We have carried out K+ ion permeation measurements across the liposome membrane in varying molar ratios at T = 283–303 K. A large overshoot and the following relaxation of the ion permeability were observed with UV irradiation at T = 293 K. We have proposed that the specific photoresponse is operated by two factors: the expansion of pores (‘quasi‐channels’) due to trans‐ti‐cis isomerization of 8A5 and the increase of the boundaries between gel phase and liquid‐crystalline phase around the phase transition temperature. FTIR spectroscopy yields useful information about the conformational fluctuations of the DMPC bilayer induced by photoisomerization of 8A5.

Photochemical control of DC current across planar bilayer lipid membranes doped with azobenzene derivative

The photoelectric properties of the planar bilayer lipid membrane (BLM) of soybean lecithin doped with an amphiphilic azobenzene derivative, 4-octyl-4′-(5-carboxypentamethyleneoxy) azobenzene (8A5), were examined. When a DC voltage is applied across the BLM, the trans-membrane current changes under alternate irradiation with ultraviolet and visible light. A comparative study on the photoresponse of soybean lecithin liposomes doped with 8A5 revealed that the photoelectric properties of the BLM result from the change in the membrane conductivity due to photoisomerization of 8A5.

Specific photoresponse of DMPC liposomes doped with azobenzene derivative around the phase transition temperature

We incorporated an amphiphilic azobenzene derivative, 4-octyl-4′-(5-carboxypentamethyleneoxy) azobenzene (8A5), into the liposome membrane of L-α-dimyristoylphosphatidylcholine (DMPC). Photoisomerization of 8A5 and changes in K + ion permeability, P cm s −1, of the membrane under irradiation with ultraviolet light were examined. The temperature of the liposome dispersion was controlled in the range T = 283–303 K. Trans-to- cis isomerization of 8A5 induces the increase of ion permeability in the whole temperature range. A specific permeability enhancement is observed around T = 290–293 K, where the ratio P(cis)/ P(trans) amounts to 200–300. It is suggested that the permeability enhancement around the phase transition temperature is caused by the increase of the phase separation boundaries as well as by the expansion of pores due to trans-to- cis isomerization.

Resonant and Nonresonant Investigations of Amphiphilic Azobenzene Derivatives in Solution and in Monolayers at the Air/Water Interface

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTResonant and Nonresonant Investigations of Amphiphilic Azobenzene Derivatives in Solution and in Monolayers at the Air/Water InterfaceJuergen Maack, Ramesh C. Ahuja, and Hiroaki TachibanaCite this: J. Phys. Chem. 1995, 99, 22, 9210–9220Publication Date (Print):June 1, 1995Publication History Published online1 May 2002Published inissue 1 June 1995https://doi.org/10.1021/j100022a039RIGHTS & PERMISSIONSArticle Views169Altmetric-Citations43LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (2 MB) Get e-Alerts

Near-field optical microscopic recording on Langmuir-Blodgett (LB) films and chemically modified surfaces

We present here our scanning near-field optical microscopic (SNOM) recording on chemically modified surfaces and Langmuir-Blodgett (LB) films. As the photochemical reaction, photocleavage of the chemically modified Si(100) surface and photoisomerization from trans- to cis-form of azobenzene moieties of an amphiphilic azobenzene derivative in the LB films were utilized. Photochemically recorded surfaces were studied with AFM and friction force microscopy (FFM). It was found that FFM can be used to read out the photochemically recorded images with a high lateral resolution.

Novel Liquid Crystalline Structure in Langmuir Monolayers of Amphiphilic Azobenzene Derivative

Depolarized Brewster-angle microscopy revealed a novel two-dimensional (2D) mesophase in Langmuir monolayers of 4-octyl-4'-(3-carboxytrimethyleneoxy) azobenzene, characterized by ubiquitous schlieren textures resulting from the long-range order of in-plane molecular orientations. The lack of half-integral strength disclinations and the presence of a regular array of π-walls, across which the in-plane orientation changes by 180 degrees, indicate the vectorial nature of the underlying order parameter. The monolayer can, therefore, be viewed as a single layer of a bulk smectic C phase or as a 2D polar nematic phase, except for the obvious absence of mirror symmetry with respect to the layer plane. In contrast to the experience with bulk liquid crystalline phases, higher-order point disclinations were often found stable in the monolayer.

Pyroelectricity and temperature-dependent domain structure of azobenzene derivative polar Langmuir-Blodgett films

An amphiphilic azobenzene derivative (AD) was used to fabricate polar pyroelectric ultrathin films by the Langmuir-Blodgett (LB) technique. The pyroelectric coefficient of the film determined at room temperature was 22 μC m −2 K −1. Independent double long spacings (31 Å and 3 Å) in the direction normal to the film were observed by an X-ray diffraction method. The UV visible spectra of the film display a blue shift from 480 nm to 380 nm compared with those of monomer molecules in solution. These results show that an H-like aggregation effect exists in the film. We also studied the temperature-dependent normal polarization intensity induced by the temperature-dependent dipole-dipole interaction in a specific domain structure as a result of the aggregation effect of AD LB films. The temperature-dependent domain structure is considered as an important factor for obtaining a large temperature-dependent spontaneous polarization and therefore a higher pyroelectricity.

Photoelectric response of a black lipid membrane containing an amphiphilic azobenzene derivative

LIPID membranes containing dye molecules that respond to light, for example by photoisomerization, may provide the basis for artificial visual systems for use in optoelectronic devices and optical transducers. Here we describe such a membrane/dye system that generates an electrical signal in response to irradiation within a specific range of wavelengths. We incorporated an amphiphilic azobenzene derivative into the planar black lipid membrane formed from egg lecithin. When a d.c. voltage is applied across the modified membrane, transient current pulses are induced by alternate irradiation with ultraviolet and visible light. We interpret this photoelectric response as the result of changes in the membrane capacitance caused by cis–trans photoisomerization of the azobenzene derivative.