NOUVEAUX MATERIAUX POUR L'OPTIQUE NON LINEAIRE QUADRATIQUE PRESENTANT UNE STRUCTURE NON CENTROSYMETRIQUE STABLE MODELISATION, SYNTHESE, MISE EN UVRE ET CARACTERISATION

STRASBOURG-Sc. et Techniques (674822102) / SudocSudocFranceF

Mesomorphism of Hybrid Siloxane-Triphenylene Star-Shaped Oligomers

Novel hybrid triphenylene-carbosiloxane liquid crystalline monomers and star-shaped oligomers have been synthesized and their thermal behavior and liquid-crystalline properties analyzed and characterized. All compounds exhibit a columnar hexagonal phase and show, particularly the oligomers, a small tendency to crystallize. The substitution pattern on the central triphenylene moiety has very different effects on the crystal to columnar phase and columnar to isotropic liquid-phase transitions. A novel sterically induced superlattice has been found, and a model for the microscopic structure is proposed. One compound could be mechanically aligned, leading to well-oriented columnar liquid crystals.Fil: Zelcer, Andrés. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; ArgentinaFil: Donnio, Bertrand. Institute Physical And Chemistry Materials De Strasbourg; FranciaFil: Bourgogne, Cyril. Institute Physical And Chemistry Materials De Strasbourg; FranciaFil: Cukiernik, Fabio Daniel. Universidad Nacional de General Sarmiento; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; ArgentinaFil: Guillon, Daniel. Institute Physical And Chemistry Materials De Strasbourg; Franci

Nematic liquid-crystalline lanthanide complexes

The classic approach to design high coordination number metallomesogens (metal-containing liquid crystals) is to attach a large number of long alkyl chains to the central coordinating unit. Although this method is often successful, it will nearly always lead to the formation of a columnar mesophase. In order to obtain lanthanide-containing metallomesogens with a nematic phase, we decoupled the mesogenic groups from the metal-coordinating group by a flexible spacer, being a long alkyl chain. This approach is illustrated for lanthanide complexes of 2-arylimidazo[4,5-f]-1,10-phenanthroline. The ligand is bearing one, two or three cyanobiphenyl groups separated form the coordinating core by long alkyl chains. Because of the structural resemblance of the pending mesogenic group to the classic nematic liquid crystal 4-pentyl-4’-cyanobiphenyl (5CB), the lanthanide complexes have a good solubility in 5CB. This is a useful property for obtaining luminescent liquid crystal mixtures. The solid complexes are highly luminescent as well. It will also be shown how room-temperature lanthanide-containing liquid crystals can be obtained.invited lecturestatus: publishe

Design of high coordination number metallomesogens by decoupling of complex-forming and mesogenic groups

Liquid-crystalline complexes of rhenium(I), yttrium(III), lanthanum(III), neodymium(III), samarium(III), europium(III), erbium(III) and ytterbium(III) were obtained by coupling mesogenic 4-cyanobiphenyl groups with a long alkyl spacer to a substituted imidazo[4,5-f]1,10-phenanthroline, which acts as the coordinating group. In the case of the rare-earth complexes, 2-thenoyltrifluoroacetonate was used as the co-ligand. All the rare-earth complexes exhibit a nematic phase, whereas the rhenium(I) complexes show a nematic, a smectic C, or a lamello-columnar phase, and the imidazole-bearing phenanthroline ligands a nematic or a smectic phase, depending on the number of attached mesogenic groups. The phase structure of the smectic and lamello-columnar phase is discussed and described on the basis of both X-ray data and dynamic molecular modeling. The lanthanide complexes are highly luminescent in the solid phase and as a solution in a nematic liquid crystal host (5CB). This approach can be generalized to obtain other high coordination number metallomesogens.oral presentation by Koen Binnemansstatus: publishe

Synclinic-anticlinic phase transition in tilted organosiloxane liquid crystals

In this paper, we considered the case of low molecular weight bimesogenic liquid crystals containing a siloxane moiety as the central part of their molecular architecture. For some of these compounds, both ferro- and antiferroelectric mesophases are present. Two distinct smectic structures can develop as a function of temperature, the first one at high temperature corresponding to a synclinic molecular arrangement with elongated molecules, and the second one at lower temperature corresponding to an anticlinic organisation with V-shaped molecules. Numerical calculations of the energy of different conformations of these bimesogenic molecules presented here indicate that there is no difference in energy between V-shaped and linear conformations regardless of the number of silicon atoms in the siloxane moiety. Thus a microscopic model of the synclinic-anticlinic phase transition is developed where the driving force is indeed a free energy difference between the two phases, and not a difference of energy between the V-shaped and linear conformations. The model explains why the anticlinic SmCA phase is more stable than the synclinic SmC one, why the synclinic SmC phase is generally the higher temperature one, and why in some organosiloxane materials the anticlinic SmCA phase is not present

Design of high coordination number metallomesogens by decoupling of the complex-forming and mesogenic groups: Nematic and lamello-columnar mesophases

Liquid-crystalline complexes of rhenium(I), yttrium(III), lanthanum(III), neodymium(III), samarium(III), europium(III), erbium(III), and ytterbium(III) were obtained by coupling mesogenic 4-cyanobiphenyl groups via a long alkyl spacer to a substituted imidazo[4,5-f]-1,10-phenanthroline, which acts as the coordinating group. In the case of the rare-earth complexes, 2-thenoyltrifluoroacetonate was used as the coligand. The rhenium(I) complexes contain the bromotricarbonylrhenium(I) moiety. All the rare-earth complexes exhibit a nematic phase, whereas the rhenium(l) complexes and the imidazole-bearing phenanthroline derivatives show a nematic or a lamellar columnar phase, depending on the number of attached mesogenic groups. The phase structures of the lamellar columnar phases are discussed and described on the basis of both X-ray diffraction data and dynamic molecular modeling. The lanthanide complexes are highly luminescent in the solid phase and as a Solution in a nematic liquid-crystal host (5CB). The approach discussed in this paper can be generalized to obtain other high coordination number metallomesogens.status: publishe