Rigid phenylene ethynylene units linked by a V-shaped centre. An approach to biaxial nematogens?

Encouraged by theoretical predictions that nematic phases formed from V-shaped compounds could be biaxial, shape-persistent phenylene ethynylene arms linked by 1,3-phenylene, 4,4′-diphenylenemethane and 3,6-fluorenone units have been synthesized. Crystallisation and micro-segregation is prevented by 2, 5-alkoxy substitution on the middle benzene ring of the arms. The specific molecular engineering, i.e. variation of peripheral substituents (H, CN) and different lengths of lateral alkoxy chains, lead to enantiotropic nematic liquid crystals over a wide temperature range for fluorenone containing materials II3d and mixtures of II3d with non-mesogenic II3b. These mesophases solidify at ambient temperature, and form nematic glasses.SCOPUS: cp.jinfo:eu-repo/semantics/publishe

Practical One-Step Synthesis of Symmetrical Liquid Crystalline Dialkyloligothiophenes for Molecular Electronic Applications

This communication describes extremely simple one-step synthesis of α,α′-dialkyloligothiophenes by the lithiation/alkylation of the corresponding commercially available oligothiophenes. Use of t-BuOK to enhance the reactivity of lithiated oligothiophene species towards alkyl halides is crucially important. Copyright © 2006 The Chemical Society of Japan.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Homeotropic alignment in films of a mesogenic phthalocyanine depends on the nature of interactions with the surface

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Self-assembly of hydrogen-bond assisted supramolecular azatriphenylene architectures

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Emission Properties of a Highly Fluorescent Pyrene Dye in Solution and in the Liquid

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Liquid Crystalline Octaalkoxycarbonyl Phthalocyanines: Design, Synthesis, Electronic Structure, Self-aggregation and Mesomorphism

We describe a practical synthesis of octaalkoxycarbonyl phthalocyanines that are well soluble in various organic solvents and form liquid crystalline columnar mesophases at room temperature. The ground-state geometry, HOMO/LUMO energies, vertical transition energies and the corresponding oscillator strengths have been calculated for the isolated molecules. The redox behavior of octaalkoxycarbonyl phthalocyanines was investigated by cyclic voltammetry and their aggregation in solution by 1H NMR spectroscopy. The supramolecular structure of the liquid crystalline mesophase of a novel phthalocyanine bearing branched alkyl chains was studied by powder X-ray diffraction. The length and branching of peripheral alkyl chains are found to be two structural parameters affecting the formation of mesophases and self-aggregation in solution. © The Royal Society of Chemistry.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Emission properties of a highly fluorescent pyrene dye in solution and in the liquid state

Three novel pyrene dyes substituted by four oligo-ether side chains of varying size have been synthesized. Surprisingly, two of these fluorescent derivatives are liquid at room temperature. The photophysical study of one of these dyes, which is miscible in common organic solvents such as hexane, chloroform and toluene, but also in water, has been performed. It has been shown that this pyrene derivative exhibits a high quantum yield of fluorescence, Φf ∼ 1, and has a high extinction coefficient, i.e. ε = 100,000 mol-1 cm-1 1, in diluted n-hexane solution. In water, aggregation takes place and the fluorescence quantum yield decreases considerably. Moreover, the spectroscopic properties of the aggregates formed in water are very close to those of the neat liquid. Therefore, the basic structure of the aggregates formed in water and in the pure liquid are expected to be similar. © 2005 Elsevier B.V. All rights reserved.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Tailoring discotic mesophases: Columnar order enforced with hydrogen bonds

Hydrogen bonding can be used to significantly enforce the intra-columnar stacking order in discotic mesogens. The ordered hexagonal columnar mesophase of a HAT-CONHR derivative is characterized by the smallest inter-disk distance ever found in columnar liquid crystals (3.18–3.20 Å). This additional attractive interaction between the disks in the column results in a regular disc stacking and thus in a high charge-carrier mobility over the whole investigated temperature range (from room temperature up to 200 °C).FLWINinfo:eu-repo/semantics/publishe

Discotic liquid crystals as electron carrier materials

A series of five new hexaalkylthiohexaazatriphenylenes 2a-e has been synthesized. Their thermotropic behaviour has been investigated and compared with the corresponding series of hexaalkylthiotriphenylenes 1a-e and hexaalkylthiohexaazatrinaphthylenes 3a-e. Unexpectedly, hexaalkylthiohexaazatriphenylenes 2a-e, hexaalkylthiotriphenylenes 1d-e and hexaalkylthiohexaazatrinaphthylenes 3e, do not form columnar liquid crystalline mesophases.SCOPUS: cp.jinfo:eu-repo/semantics/publishe

Highly fluorescent crystalline and liquid crystalline columnar phases of pyrene-based structures

7 pages, 6 figures, 2 tables, 2 schemes.-- et al.A concept for highly ordered solid-state structures with bright fluorescence is proposed: liquid crystals based on tetraethynylpyrene chromophores, where the rigid core is functionalized with flexible, promesogenic alkoxy chains. The synthesis of this novel material is presented. The thermotropic properties are studied by means of differential scanning calorimetry (DSC), cross-polarized optical microscopy (POM), and X-ray diffraction. The mesogen possesses an enantiotropic Colh phase over a large temperature range before clearing. The material is highly fluorescent in solution and, most remarkably, in the condensed state, with a broad, strongly red shifted emission. Fluorescence quantum yields (ΦF) have been determined to be 70% in dichloromethane solution and 62% in the solid state. Concentration- and temperature-dependent absorption and emission studies as well as quantum-chemical calculations on isolated molecules and dimers are used to clarify the type of intermolecular interactions present as well as their influence on the fluorescence quantum yield and spectral properties of the material. The high luminescence efficiency in the solid state is ascribed to rotated chromophores, leading to an optically allowed lowest optical transition.This work was financially supported by the Belgian National Science Foundation (FNRS- FRFC no. 2.4608.04, FNRS “crédit aux chercheurs” no. 1.5.074.00), Université Libre de Bruxelles, Banque Nationale de Belgique, Communauté Francüaise de Belgique (ARC no. 00/05-257), and European Union (DISCEL G5RD-CT-2000-00321). V.d.H. and J.T. acknowledge FRIA for a fellowship. A.K. thanks the Royal Society and Peterhouse for financial support. J.C. is a FNRS research fellow.Peer reviewe