Synthesis and photochromic properties of a bis(diarylethene)-naphthopyran hybrid

The synthesis and photochromic properties of a triphotochromic molecule consisting of one naphthopyran flanked by two diarylethene units investigated by UV-Visible and NMR spectroscopies are reported. Six different states resulting from the open/closed naphthopyran associated with one or two open/cyclized diarylethenes have been characterized. Switching of the naphthopyran group is possible, independently of the state of the diarylethene groups, permitting the controlled generation of electronically connected diarylethene groups. However, the diarylethene groups cannot be closed if the naphthopyran group is open

Mononuclear Cu(II) complexes of novel salicylidene Schiff bases: synthesis and mesogenic properties

Two new Schiff base ligands 1 and 2 (where 1 = 4-(2-hydroxybenzilidenamino)-phenyl-4-(decyloxy)-2-(pent-4-enyloxy)benzoate, 2 = 4-(4-(decyloxy)-2-hydroxybenziliden amino)-phenyl-4-(decyloxy)-2-(pent-4-enyloxy)benzoate) and their copper (Cu)(II) complexes have been synthesised and characterised. The derivatives were fully characterised structurally, and their mesomorphic behaviour was investigated by polarised optical microscopyand differential scanning calorimetry. The structure of Cu(II) complex having 1 as ligand (3) was determined by X-ray diffraction. The Schiff base ligands exhibit enantiotropic nematic phases, the Cu(II) complex 4 shows monotropic nematic phase behaviour, while compound 3 does not show mesomorphism

Helically Twisted Chiral Arrays of Gold Nanoparticles Coated with a Cholesterol Mesogen

Gold nanoparticles have been prepared and surface-functionalized with a 1:1 molar mixture of a hexylthiol ligand and a chiral mesogenic ligand consisting of a cholesterylbenzoate attached via an undecylthiol spacer. Grazing incidence X-ray diffraction showed that upon annealing a columnar liquid crystal (LC) structure develops with the nanoparticles forming strings on a regular oblique 2d lattice. Synchrotron radiation circular dichroism is substantially enhanced upon the isotropic− LC transition. In the proposed structural model, layers of Au columns rotate by a small angle relative to their neighbors, with the columns winding around a helical axis. The work demonstrates that it is possible to obtain chiral LC superstructures from nanoparticles coated with chiral mesogen without the addition of a separate LC or chiral dopants. The results provide direction in the development of plasmonic metamaterials interacting selectively with circularly polarized light

Chemistry and photochemistry of novel aromatic spiroketals derived from 2,6-bis(5-bromo-2-hydroxybenzylidene) cyclohexanone

Natural colorants such as flavylium and xanthylium derivatives have attracted considerable interest in the last decades due to their potential health effects and replacement of synthetic pigments. In addition, these type of compounds exhibit versatile photochromic properties by switching from a variety of colourswhen submitted to different external stimuli[1-3]. The aim of the present work was to design novel photochromic systems based on xanthylium derivatives. Therefore, we have synthesized and characterized 2,6-bis(5-bromo-2- hydroxybenzylidene)cyclohexanone. The network of chemical reactions when submitted to light and different pH values has been investigated. A new colorless compound 3,11-dibromo7,8-dihydro-6H-chromeno[3,2-d]xanthenes(Scheme 1) isolated from the equilibrated solution of trans-chalcone specie in methanolhave been isolated and fully characterized by NMR and X-ray diffraction. The rate of the reaction increased when the solution of trans-chalcone was exposed to sunlight. The spiroketal form was stable at in neutral and basic conditions, while at low pH values it converts into xantylium cationic form

Toxicological evaluation of the organic phase resulted from the COSORB process

In this work, the toxicological assesment of the organic phase resulted from the COSORB process was performed. For this purpose, an animal model was used to evaluate the effects of the organic phase on skin physiological parameters after topical application to SKH-1 hairless mice. The obtained results revealed that the constituents of the organic phase induce skin toxicity by disturbing the physiological skin parameters status, which represents the first signs of skin pathology

Supramolecular "soft" assemblies based on copper (I) coordination complexes

Copper(I) coordination complexes with N^N chelating oligopyridines are valuable candidates for applications in solar energy conversion1 or lightning technologies2 because of their excellent photophysical and photochemical properties and for the low cost and ready availability of the metal. The most attractive systems are based on ligands able to stabilise their tetrahedral geometry (D2d symmetry) and to hinder the flattening distortions which facilitates oxidation to Cu(II) species.3 Herein we present the synthesis and characterisation of new stable Cu(I) complexes based on functionalised 2,2’-biquinoline ligands (Figure 1) that self-assemble into “soft” supramolecular architectures. The stoichiometry and purity of all compounds were determined using elemental analyses, Atomic Absorption, IR and 1H NMR spectroscopies. The functionalisation of the biquinoline ligand with long alkyl chains yielded thermotropic liquid crystalline systems (CuL1_X and CuL2_X), whereas insertion of hydrophilic groups promoted the assembly in water into supramolecular aggregates (CuL3_X). The thermal behaviour of complexes CuLn_X with n = 1 and 2 was investigated by polarized optical microscopy (POM) and differential scanning calorimetry (DSC). UV-Vis studies on CuL3_X evidenced the presence of supramolecular aggregates in water. Stabilization of Cu(I) systems can be also achieved by building supramolecular assemblies and thus blocking the fluxional process towards a distorted “Cu(II)-like” geometry in concentrated solution of complexes

Novel asymmetric benzylidenecyclohexanone photochromic compound as food dye with antioxidant properties

Nature has always been the provider of compounds with unique properties and amazing application within or outside the living organisms [1]. Color is certainly one of the natural features that have always fascinated researchers from almost all fields of knowledge and compounds with such properties have been isolated from raw materials or have been designed and synthesized based thereon [2]. Flavylium derivatives are natural or synthetic compounds responsible for certain color of fruits and flowers and are able to turn from yellow to red and blue depending on the pH of the media [3]. They are also studied for their photochromic behavior when excited with different wavelengths and their network of chemical transformation has been the subject of many research papers [4,5]. We have focused lately on the synthesis of xanthylium derivatives [6], compounds similar in behavior with flavylium ones with symmetrical and asymmetrical substituents on the aromatic rings. The photochromic behavior of the new asymmetric benzylidene cyclohexanone derivative 4-(p-hydroxybenzylidene)-6-hydroxy-1,2,3,4-tetrahydroxanthylium chloride (HTX)in aqueous solution at different pH values was studied using UV-Vis, NMR and fluorescence spectroscopy. In strong acid environment HTX exhibits purple color and a broad absorption band at about 516 nm, corresponding to the presence of the xanthylium cation, while in basic conditions the solutions are red, with an absorption band at about 596 nm. At pH ranging from 9 to 12 HTX is bluish and suffers spontaneous transformations between species involved in the network of chemical reactions. HTX shows good fluorescence behavior at all pH values. HTX has a good antioxidant character of 55.15% determined by DPPH method. The features described above and its curcumin origin would highly recommend it for application in the field of food colorants