Philippe Berdagué

New laterally aromatic branched liquid crystal materials with large nematic ranges

Abstract Three new homologous series of mesogens containing three rings in the main structure and a lateral aromatic branch have been synthesized. When the lateral aromatic branch is attached to the middle ring, monotropic phases are observed, and there is a strong tendency to form the smectic C phase. When the lateral aromatic branch is attached to an outer ring, the compounds possess purely enantiotropic nematic phases. The terminal alkoxy chain in the outer ring which has a lateral aromatic substituent can be replaced by a rigid group without disturbing the large nematic range. Selective introduction of a particular substitutent may be useful for the construction of devices possessing desirable characteristics such as non-linear optical properties.

Change of the lateral chain conformation in the solid and the nematic phase in laterally substituted nematogens

Abstract A new homologous series of 4-(4′-ethoxybenzoyloxy)-2-alkoxy-4′-(4-butoxysalicylaldimine)-azobenzenes has been synthesized. These compounds contain four rings in the main core and a lateral alkoxy branch on one of the inner rings and present enantiotropic nematic properties. The X-ray crystal structure (MoKα radiation, λ = 0.7071 A, graphite monochromator) of 4-(4′-ethoxybenzoyloxy)-2-butoxy-4′-(4-butoxysalicylaldimine)azobenzene was investigated (T = 293K, R = 0.059 for the 2855 observed reflections). This compound (C36H39N3O6) crystallizes in the monoclinic system with C2/c space group; (Z = 8); a = 28.052(7) A, b = 7.545(4) A, c = 33.823(7) A and β = 112.70(1)°. There is a strong chelated hydrogen bond between the OH group and the neighbouring nitrogen atom engaged in the imine bridge. In the solid state, the molecule is roughly linear with a 31 A length. The lateral butoxy chain is quasi-perpendicular to the long axis of the main core. The crystal cohesion is due to numerous Van der Waals inte...

Nematogens with more flexible chains than aromatic rings in the core

Mesogens containing four rings in the main core can accommodate one terminal and two nearby lateral chains on each outside aromatic ring. These compounds containing six chains present an enantiotropic nematic range which is influenced by the rigidity of the links. The conformational behaviour of the first methyleneoxy group within the chains was investigated by one and two dimensional C-13 NMR. The sign of the jump in chemical shifts when entering the nematic phase indicates the folding of each lateral branch. Dipolar oscillations during cross-polarization contact provide the values of the bond order parameter. The two First lateral fragments do not behave in the same way, demonstrating the influence of the fragment along which the chain is back: folded.

Gas chromatographic properties of some liquid crystals containing dioxyethylene ether terminal chains

SummaryComparative gas chromatographic properties of four rod-like liquid crystals coated on capillary columns are studied. These four liquid crystals contain the same number of atoms in their backbones. They differ by the partial or total replacement of the two terminal heptyloxy chains by a 2-(2-methoxyethoxy)ethoxy (called also dioxyethylene ether) chain. Synthesis and thermal properties of these four liquid crystals are presented. It appears that the introduction of dioxyethylene ether decreases the two transition temperatures as well as the nematic range. With regards to the chromatographic separation abilities, the four liquid crystals are efficient before and after solid-nematic or nematic-liquid transitions; however, the plate numbers are higher in the nematic state. Interesting analytical applications are demonstrated in different fields: isomeric separation of alkanes, aromatics, polyaromatics, volatile aroma compounds, cis and trans isomers and phenols. The increase of the number of oxyethylene units permits to drastically increase the separation efficiency for polar solutes.

Nematogens containing oxyethylene units at a lateral or terminal position and their mixtures with salts

Short terminal polyoxyethylene chains may be introduced into mesogens containing lateral substituents such as two hexyloxy chains or a crown-ether fragment. These compounds have a large nematic range near room temperature and can dissolve large amounts of the salt LiBF4 without destroying the nematic arrangment. In the nematic phase, the ions are ordered and the quadrupolar splitting associated with these ions can allow this ordering to be monitored. Increasing the salt concentration does not seem to change the ordering of the individual ions. The 13C thermal evolution of the field-induced chemical shift in the oxyethylene (OE) units with or without salt does not show any real difference, indicating that the interaction between the ions and the mesogen is small. This means that there is very little change in conformation in the OE unit when adding salt to the mesogen.

New chemically bonded liquid crystal for high-performance liquid chromatography: Synthesis, characterization and chromatographic behaviour

SummaryA new bonded liquid-crystal stationary phase has been developed for high-performance liquid chromatography. The method includes the synthesis of 4-(4-carboxybenzyloxy)-3-methyl-2-dodecyloxy-4′-(2-(4′-dodecyloxybenzyl)-ethylene-azobenzene (ALC) which reacts with LiChrospher Si 100 NH2 to give the bonded stationary phase (denoted BLC). Characterization of ALC and the BLC were performed by differential scanning calorimetry (DSC), proton NMR, solid-state13C NMR and elemental analysis. The specific surface area of the BLC was determined by BET. The chromatographic behaviour of the BLC was investigated in both normal-and reversed-phase modes. As a normal phase, a temperature transition is found in the 315–330 K range which leads to remarkable analytical properties. The retention factors of phenanthrene and anthracene increased when the temperature was increased from below to above the transition temperature. In the reversed-phase mode, the behaviour of the BLC seemed more complex, two temperature transitions being apparent. Separation of xylene and diethylbenzene isomers was possible at temperatures above the temperature range of the transitions.

Ordering of some liquid crystals containing the 2-phenylindazole core

Molecules containing the 2-phenylindazole core present liquid crystalline properties even if the two terminal chains do not point along the same axis. 13CNMR in the liquid crystalline phase shows that the molecular long axis is nearly aligned with the para-axis of the phenyl moiety of the 2-phenylindazole core. This implies that the first fragments of the chain belonging to the indazole moiety do not lie along the molecular long axis. To promote liquid crystal properties, this chain needs to possess at least six carbon atoms.

Correlation 2D-NMR experiments involving both 13C and 2H isotopes in oriented media: methodological developments and analytical applications†

Correlation 2D‐NMR experiments for 13C and 2H isotopes turn out to be powerful methods for the assignment of the quadrupolar doublets in the 2H NMR spectra of isotopically modified (polydeuterated or perdeuterated) or unmodified solutes in homogeneously oriented solvents, such as thermotropic systems or lyotropic liquid crystals. We review here the different pulse sequences, which have been employed, their properties, and their most salient applications. These 2D‐NMR sequences have been used for (i) 13C–2H correlation with and without 1H relay and (ii) 2H–2H correlation with 13C relay. The 13C–2H correlation experiments without 1H relay have been achieved for specifically deuterated or non‐selectively deuterated analytes, but also more recently for isotopically unmodified ones thanks to the high sensitivity of very high‐field NMR spectrometers (21.1 T) equipped with cryogenic probes. The 13C–2H correlation 2D‐NMR experiments are especially useful for the assignment of overcrowded deuterium spectra because the 2H signals are correlated to 13C signals, which benefit from a much larger dispersion of chemical shifts. In this contribution, particular attention will be paid to the use of correlation 2D‐NMR experiments for 2H and 13C nuclei in weakly aligning, polypeptide oriented chiral solvents, because these methods are useful and original tools for enantiomeric and enantiotopic analyses. Copyright

Use of two-dimensional correlation between 2H quadrupolar splittings and 13C CSA's for assignment of NMR spectra in chiral nematics

The possibility of correlating visible spectral enantiodiscriminations in a single 2D map using simultaneously both quadrupolar and dipolar nuclei is presented and experimentally demonstrated. The method uses deuterium–carbon-13 heteronuclear 2D experiments with 13C in natural abundance applied to deuterated compounds oriented in chiral, nematic liquid crystals (PBLG/CHCl3). Illustrative examples involving chiral and prochiral solute molecules are analysed and discussed. We show that this approach provides an efficient and elegant way to assign deuterium resonances for each enantiomer or enantiotopic directions in prochiral molecules.

Nematogens incorporating a lateral flexible ring

A lateral flexible ring can be introduced on a mesogenic core containing four rings. Lateral aliphatic rings containing up to 12 atoms have been synthesized. Despite this large lateral protruding substituent, a large nematic range is obtained. A compound with a benzo15-crown-5 lateral ring has been successfully obtained and shows the possibility of designing nematic liquid crystals with a crown ether moiety at a lateral position.