Ana Omenat

High charge mobility in discotic liquid-crystalline triindoles: just a core business?

This work has been supported by CTQ2007-65683/BQU, (CTQ2009- 09030), S2009/MAT-1756/CAM, MiUR through the PRIN 2007 (2007WJMF2W) project, Gobierno de Aragon, 200960I086 PIE.

Self-organization of nanostructured functional dendrimers

In this article, we review some of our recent work on the development and study of the properties of self-organizing supermolecular liquid crystalline dendritic materials. Prior to this purpose, the state of the art in the field of molecular design, structure and properties of liquid-crystalline dendrimers (LCDs) will be briefly reviewed, and illustrated by a selection of pioneering examples. The first type of LC dendrimer takes into account the location of their functional elements (mesogens) in the periphery of the macromolecules and its topology of attachment, and the nature of the mesogen. We will show how functionality can be in-built into such materials so that self-organising functional systems can be created. Side-chain liquid-crystalline dendrimers exhibiting lamellar, columnar and nematic phases are shown. The mechanism of mesophase formation (mesogen interaction versus microphase separation) is also discussed in relation to the molecular structure (the nature of the mesogen and of the dendritic matrix, dendritic generation number). The second type of LC dendrimer introduced presents a different topology in that the mesogens are now inserted within the dendritic matrix and in the periphery. Owing to their particular constitution, it will be shown that the mesophases of the lamellar and columnar types possess unusual morphologies.

Sugar-Coated Discotic Liquid Crystals

The constitutional marriage between a classical thermotropic discotic molecule and carbohydrate-based amphiphiles (e.g., see Figure) is shown to result in hybrid compounds, where, for example, a triphenylene unit serves as the central core from which oligomethyleneoxy chains terminated with sugar residues radiate, which have interesting liquid crystal properties

Copper-containing dendromesogens: the influence of the metal on the mesomorphism

The synthesis and liquid crystalline behaviour of the first and second generations of a dendrimeric structure based on poly(propyleneimine)(DAB-dendr(NH2)x) are reported. 4-(4-n-Alkoxybenzoyloxy)salicylaldehydes are used as mesogenic moieties attached at the peripheral amino groups of the dendrimers giving rise to dendromesogens with four and eight mesogenic branches. From these dendromesogens, considered as organic ligands, were prepared six metal-containing dendrimers which incorporate two or four copper atoms in their structures. All the dendrimeric ligands and three of the metal-containing dendrimers exhibit liquid crystalline properties which were studied by optical microscopy, DSC, X-ray diffraction and EPR spectroscopy.

Highly ordered π-extended discotic liquid-crystalline triindoles

New π-extended discotic liquid crystals based on heptacyclic triindole have been synthesized and their mesomorphic behaviour investigated. The synthesis of π-extended compounds was carried out by oxidative cyclodehydrogenation of differently substituted star-shaped hexaaryltriindoles to afford the planar derivatives with an extended core. Extending the conjugation in these materials results in a significant increase in the order and range of the mesophases. The influence of the peripherally attached groups in the mesomorphic and electronic properties offers a great opportunity to further tune the properties of these compounds intended to their incorporation in devices.

Structural study of metallomesogens derived from tris-[2-(salicylideneamino)ethyl]amine. A molecular meccano

The synthesis of new metal complexes based on imines derived from tris-(2-aminoethyl)amine (TREN) which exhibit different geometries depending on the metal [Cu(II), VO(IV), Pd(II), Ni(II), Ln(III)] has been carried out. TREN has three coordination positions which allow us to obtain different coordination complexes involving one, two or three metallic centres. The molecular structure and purity of these novel compounds have been verified by IR, 1H and 13C NMR and elemental analysis and electro-spray mass spectrometry. The phase behaviour was studied by polarizing optical microscopy, differential scanning calorimetry (DSC) and X-ray diffraction techniques. It was found that the transition metal complexes display a smectic C mesophase whereas the lanthanide complexes display an unidentified smectic mesophase.

A polymer network prepared by the thiol-yne photocrosslinking of a liquid crystalline dendrimer

A polymer network is prepared by the thiol-yne photopolymerization of multifunctional dendrimer with a tetrathiol crosslinker. The network obtained shows a liquid crystalline phase at room temperature, which has been characterized by optical microscopy, differential scanning calorimetry, and X-ray diffraction. Photoinduced deformation of uniaxially aligned free-standing films of the photocrosslinked material has been demonstrated.

Liquid crystalline semifluorinated ionic dendrimers

Poly(propyleneimine) [PPI‐(NH2) n ] and poly(amidoamine) [PAMAM‐(NH2) n ] dendrimers with n = 4, 8, 16, 32 and 64, have been functionalized with a semifluorinated carboxylic acid [CF3(CF2)7CH2CH2COOH] on the surface. The thermal and liquid crystal properties of the resulting ionic dendrimers have been studied by polarized optical microscopy (POM), differential scanning calorimetry (DSC) and X‐ray diffraction (XRD). All dendrimers show a smectic A (SmA) mesophase, except that derived from the fifth generation of PPI, which displays a columnar mesophase. The mesomorphic behaviour of the dendrimers is attributed to the formation of ionic bonds and to the microsegregation of the dendritic branches and the fluorinated peripheral chains.

Molecular morphology and mesomorphism in dendrimers: a competition between rods and discs

The synthesis and liquid crystalline behaviour of several sixteen-branched dendrimers based on poly(amidoamine) (PAMAM) and poly(propyleneimine) (DAB) are reported. Mono-, di- and trialkoxybenzoyloxysalicylaldehydes are used as mesogenic promotor moieties and are attached at the peripheral amino groups of the pre-existing dendrimers. All the compounds exhibit liquid crystalline properties which were studied by optical microscopy, DSC and X-ray diffraction. The relationship between the structure of the mesogenic units and the mesomorphic behaviour is discussed and models for the different supramolecular organizations are proposed.

New Chiral Smectic Liquid Crystals with The Assymetrical Carbon in The Central Part of The Molecule

Abstract A new family of mesogenic compounds has been synthesized. The series consists of seven chiral dimers with the chiral center in the central flexible spacer of the dimeric structure. All of the materials are mesomorphic. Most of them exhibit tilted smectic phases and consequently could be of interest as the first ferroelectric liquid crystals with the chiral center in the central core of the molecule.