Azophenyl Group Research Articles

Syntheses and properties of imidazolium-based quaternary salts with D-π-A unit containing azobenzene groups

Several novel organic ionic salts containing azophenyl groups with d-π-A structural unit was synthesized through the quaternization of azophenyl imidazole derivatives and 2, 4-dinitro-chlorobenzene in refluxing xylene. The donor-acceptor structure of the new ionic salts was characterized by the UV–vis, IR, ESI-MS, and NMR spectra. And the structure of ionic salt 8 was also evidenced by its single crystal X-ray diffusion. The UV−visible absorption spectra of all compounds exhibited two major strong absorption bands about at 340 and 440 nm, attributed to the strong intra-molecular π-π* and n-π* charge transfer of the azophenyl group, respectively. The results on thermal properties of ionic salts showed that all ionic salts 7–12 with d-π-A structural unit have better thermal stabilities and higher decomposition temperatures, and ionic salt 10 has the lowest melting point at 114 °C, almost close in the temperature range of ionic liquids. The electronic effect of substituted group has a certainly effect on the absorption spectra of azophenyl group and thermal properties of ionic salt with d-π-A structural unit.

β-Cyclodextrin-Modified Mesoporous Silica Nanoparticles with Photo-Responsive Gatekeepers for Controlled Release of Hexaconazole

In the present research, photo-responsive controlled-release hexaconazole (Hex) nanoparticles (Nps) were successfully prepared with azobenzene (Azo)-modified bimodal mesoporous silica (BMMs), in which β-cyclodextrin (β-CD) was capped onto the BMMs-Azo surface via host–guest interactions (Hex@BMMs/Azo/β-CD). Scanning electron microscopy (SEM) confirmed that the nanoparticles had a spherical structure, and their average diameter determined by dynamic light scattering (DLS) was found to be 387.2 ± 3.8 nm. X-ray powder-diffraction analysis and N2-adsorption measurements indicated that Hex was loaded into the pores of the mesoporous structure, but the structure of the mesoporous composite was not destroyed. The loading capacity of Hex@BMMs/Azo/β-CD nanoparticles for Hex was approximately 27.3%. Elemental components of the nanoparticles were characterized by X-ray photoelectron spectroscopy (XPS) and electron dispersive spectroscopy (EDS). Ultraviolet–visible-light (UV–Vis) absorption spectroscopy tests showed that the azophenyl group in BMMs-Azo undergoes effective and reversible cis-trans isomerization under UV–Vis irradiation. Hex@BMMs/Azo/β-CD Nps exhibited excellent light-sensitive controlled-release performance. The release of Hex was much higher under UV irradiation than that in the dark, which could be demonstrated by the bioactivity test. The nanoparticles also displayed excellent pH-responsive properties, and the sustained-release curves were described by the Ritger–Peppas release kinetic model. BMMs nanocarriers had good biological safety and provided a basis for the development of sustainable agriculture in the future.

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.

Synthesis and Dimerization Studies of a Lipophilic Photoresponsive Aryl-Extended Tetraurea-Calix[4]pyrrole.

We describe the syntheses of the lipophilic aryl-extended α,α,α,α-tetraurea-phenyl-calix[4]pyrrole 1, featuring four appended azo-phenyl groups with two tert-butoxy carbonyl meta-substituents and its photo-inactive counterpart 2. In CD2 Cl2 solutions, both tetraurea-calix[4]pyrroles self-assemble into dimeric capsules by encapsulating one molecule of a suitable bis-N-oxide or two molecules of a mono-N-oxide. The dimeric capsules are mainly stabilized by a cyclic array of sixteen hydrogen bonds established between the eight unidirectionally oriented urea groups. Photoirradiation experiments demonstrated the trans-to-cis isomerization of the azo-phenyl groups and the formation of a plethora of stereo isomeric cis-azo-enriched capsular assemblies. The highly cis-azo enriched capsular assemblies seem to show a reduced stability and their involvement in equilibria with non-capsular counterparts that also bind the N-oxides. The thermally induced cis-to-trans interconversion processes demonstrated the reversibility of the photoisomerization and the photostability of most binding partners. An equimolar mixture of the two tetraureas produced two homodimeric capsules and the heterodimeric counterpart in a ratio close to statistical distribution.

Multistimuli-responsive supramolecular assembly of cucurbituril/cyclodextrin pairs with an azobenzene-containing bispyridinium guest.

A linear supramolecular architecture was successfully constructed by the inclusion complexation of α-cyclodextrin with azobenzene and the host-stabilized charge-transfer interaction of naphthalene and a bispyridinium guest with cucurbit[8]uril in water, which was comprehensively characterized by (1)H NMR spectroscopy, UV/Vis absorption, fluorescence, circular dichroism spectroscopy, dynamic laser scattering, and microscopic observations. Significantly, because it benefits from the photoinduced isomerization of the azophenyl group and the chemical reduction of bispyridinium moiety with noncovalent connections, the assembly/disassembly process of this supramolecular nanostructure can be efficiently modulated by external stimuli, including temperature, UV and visible-light irradiation, and chemical redox.

Hierarchical Organization of Spherical Assembly with Reversibly Photocontrollable Cross-Links

A ternary photocontrollable assembly was hierarchically constructed by the "orthogonal" host-guest interaction of different types of cyclodextrins toward the porphyrin and azobenzene. Spectroscopic titrations and microscopic investigations demonstrate that the inclusion complex of azobenzene modified water-soluble porphyrin (1) with phthalocyanine-grafted permethyl β-cyclodextrins (2) could be reversibly cross-linked to relatively larger nanospheres with naphthyl bridged bis(α-cyclodextrin)s (3). Moreover, the large-sized spheres (1·2·3) could be disassembled and switched to small-sized complex (1·2) upon the photoinduced isomerization of an azophenyl group.

Synthesis and characterization of novel azo-embedded N-confused tetraphenylporphyrin

A unique class of azo porphyrin, 5,10,15,20-tetraphenyl-21-phenylazo-(2-aza-21-carbaporphyrin 1, in which an azophenyl group is embedded in N -confused porphyrin, was synthesized and characterized by 1 H NMR, 13 C NMR, UV-vis absorption, MS, and X-ray crystallographic analysis. Synthesis of 1 was achieved through a coupling reaction of 21-amino N -confused tetraphenylporphyrin with nitrosobenzene and subsequent deoxygenation of resulting azoxy derivative with a trioxo rhenium(VII) N -fused porphyrinato catalyst. The azo-conjugate molecule was exclusively obtained as a trans-isomer and no isomerization to the cis-isomer was observed under thermal or photoirradiation. The absorption spectrum of 1 shows a moderate red-shift due to the effective interaction between the porphyrinic π-system and the connecting azophenyl group. Upon protonation, this effect is essentially lost as a result of removing degeneracy of LUMO and LUMO+1.

New Azothiacalix[4]arenes Containing Biheterocyclic Subunits: Extraction and Complexation Properties

New thiacalix[4]arenes 2a, 3a, 4 and 5 functionalized with biheterocyclic and azophenyl groups at the lower rim and the upper rim of the macrocycle, respectively, were synthesized and their extraction properties towards Cu2+, Ag+, Ni2+ and Pb2+ studied. The complexation properties of the bithiazolyl receptors 2a, 4 and the bipyridyl receptors 3a, 5 were investigated by fluorescence and UV–visible titrations, respectively. The stoichiometries of the complexes were determined. A stoichiometry of 1:1 was found for the Cu-2a, Ag-3a complexes and 2:1 for the Cu2-4, Ag2-5 complexes as a function of the number of grafted bithiazolyl groups. The association constants for the 1:1 complexes were calculated using the Benesi–Hildebrand plot and by linear regression analysis.

Tetrahedral manganese(II) complexes of 1-alkyl-2-(arylazo)imidazoles. X-ray crystal structure of [Mn(HaaiMe)4](ClO4)2·DMF (HaaiMe = 1-methyl-2-(phenylazo)imidazole)

[Mn(RaaiR′)4](ClO4)2 complexes have been synthesised by reacting Mn(ClO4)2·6H2O and RaaiR′ in methanol (RaaiR′ = 1-alkyl-2-arylazo)imidazole, R = H (a), Me (b), Cl (c); R′ = Me (1), Et (2)). The orange–red crystalline compounds were characterised by microanalytical, spectroscopic, magnetic, thermal and electrochemical data. A single-crystal X-ray diffraction study of a DMF adduct of 1a revealed tetrahedral orientation of four ligands coordinating through imidazole-N while the azophenyl group (–N=N–Ph) is pendant. Cyclic voltammetry shows the Mn(III)/Mn(II) couple at > 1.0 V along with azo reductions.

Regioselective complexation of metal ion in chromogenic calix[4]biscrowns.

A series of 1,3-alternate chromogenic azo-coupled calix[4]biscrowns in which the crown size varied with crown-5 and crown-6 have been synthesized. From the results of UV/vis band shift upon metal ion complexation, metal ions were entrapped only by the upper crown loop, causing the hypsochromic shift on the UV/vis spectra. Calix[4]bis(crown-5)(crown-6) revealed K(+) ion selectivity while calix[4]bis(crown-6)(crown-6) showed Cs(+) ion selectivity caused by a size complementarity between hosts and guest ions. From the UV band shift of 4 in which the NO(2) group is replaced by the NH(2) group, we observed bathochromic shift upon the metal ion addition, indicating that the metal ion is encapsulated in the lower crown ring because of strengthened pi-cation interaction by introducing the electron-donating NH(2) unit regardless of the steric hindrance between two azo-phenyl groups adjacent to the crown ring.

New chromogenic azocalix[4]arene podands incorporating 2,2′-bipyridyl subunitsElectronic supplementary information (ESI) available: mole ratio plot for mixtures of 4a and Zn(CF3SO3)2; UV-Vis spectra for 4a (5 × 10–6 mol l–1) when Zn2+ (5 × 10–5 mol l–1) is added to the CH2Cl2 host solution. See http://www.rsc.org/suppdata/nj/b2/b209528a/

Six new calix[4]arenes 2, 3 and 4 functionalized with 2,2′-bipyridyl and azophenyl groups at the lower rim and the upper rim respectively have been synthesized and their complexing properties towards Zn2+ have been determined by UV-Vis titrations in organic media. The conformational properties of these ligands were obtained by 1H NMR spectroscopy. The stoichiometries of zinc complexes were determined by both the mole ratio method and Job plots. A stoichiometry of 1∶1 was found for the complexes Zn-2 and Zn-3 and 1∶2 for the complex Zn-4 as a function of the number of grafted bipyridyl groups. The association constants for 1∶1 complexes were determined by using the Benesi–Hildebrand plot and also by linear regression analysis.

Liquid crystalline polymers: The effects of chain disruptors

Abstract

Synthesis and characterization of glycidyl ethers modified by mesogenic units

New types of epoxy compounds containing biphenyl and azophenyl groups were synthesized. Model glycidyl ethers with one epoxy group were prepared to study the first reaction steps during the curing process. Diglycidyl ethers with or without a hexamethylene spacer were made to obtain epoxy networks. The structures of some intermediates and of the epoxy compounds synthesized were confirmed by Proton and Carbon-13 NMR spectroscopy.

The anatomy of an antigen molecule: Functional subregions of [formula omitted

The structural components of antigen molecules that interact with class II major histocompability complex (MHC) molecules on antigen-presenting cells (APCs) (agretopes) and with antigen receptors of T-lymphocytes (epitopes) in class II restricted T-cell responses have not been precisely defined. This issue was addressed here using murine T-eell clones specific for the simple immunogen l - tyrosine-p- azobenzenearsonate (ABA-tyr) and a series of analogs of the homologous antigen. Two experimental approaches were used. First, APCs were pulsed with analogs and used to stimulate T-cell proliferation. The patterns of stimulation segregated the clones into two specificity groups and indicated that the epitope recognized by the T-cell included the arsonate group and elements in the side chain of tyrosine. Furthermore, the clones manifest different sensitivities to antigen. Second, non-stimulatory analogs were used to block the presentation of ABA-tyr in an effort to define the agretope. Compounds containing the azophenyl group blocked presentation of ABA-tyr in a dose-dependent fashion, whereas p-arsanilic acid and l-tyrosine were ineffective. The blocking was specific inasmuch as the compounds had no effect on the antigen-induced proliferative responses of giant keyhole limpet hemocyanin (KLH) or hen egg white lysozyme (HEL)-reactive T-cell clones. The blocking pattern indicated that the feature required for productive association with the APC centered on the planar structure of the azo-linked aromatic rings, with little or no contribution from either the arsonate moiety or the tyrosyl side chain. We propose that this structure forms an agretope for this family of compounds.