Synthesis, characterization and crystal structures of two polyphilic mesogenic compounds

Three homologous series of semi-perfluorinated liquid crystals: 4-(2,2,3,3,4,4,4-heptafluoro-butyloxycarbonyl)phenyl, 4-(2,2,3,3,4,4,5,5-octafluoropentyloxycarbonyl)phenyl and 4-(3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctyloxycarbonyl)phenyl 4-[(n-perfluoroalkyl)alkyloxy]benzoates have been synthesized. Their mesomorphic properties were studied by DSC, microscopic observation and X-ray diffraction. Their layer spacings are smaller than the molecular length (L). The ratio d_SA/L is about 0.7. The crystal structure of two derivatives of the first family have also been investigated. In both structures the molecules pack in smectic C-like sheets where neighbouring molecules are antiparallel, interacting through dipolar and van der Waals forces. The interactions between contiguous sheets, through the ends of perfluorinated chains are very weak. The X-ray diffraction results on the mesophases and on the crystalline structures of two compounds of the first family are compared. From this, we propose a model of the smectic phases with a zig-zag structure.     

A pure reentrant cholesteric phase

Abstract

An optically active derivative of p-cyanobiphenyl exhibits a stable reentrant cholesteric phase with the seuqnce: K N?S_A N?I.     

New Series Exhibiting Pure Enantiotropic Nematic Reentrant Compounds at Atmospheric Pressure

Some derivatives of an homologous series of 4-aIkoxy-benzoyloxy-4′-cyanotolanes are synthesized. Two of them exhibit a stable nematic reentrant phase at atmospheric pressure.     

Synthesis and characterization of thermotropic amphiphilic liquid crystals: semiperfluoroalkyl-β-D-glucopyranosides

As part of our study of the mesomorphic properties of glucopyranosides containing fluorinated chains, this paper focuses on an investigation of the liquid crystalline behaviour of nonaromatic compounds. The synthesis of eight single-tailed materials which contain a semiperfluoroalkyl chain linked to the polar glucose head group is described. Using polarized optical microscopy, DSC and X-ray diffraction all the materials were found to show only monomesomorphism, a smectic A phase with bimolecular layers. The thermal behaviour is discussed in comparison with the previously reported data on the series of parent compounds.     

Synthesis, characterization and crystal structure of mesogenic compounds with an alkyloxy and a semi-perfluorinated chain. Influence of the alkyloxy chain length on molecular arrangement and molecular interactions

This paper describes the synthesis and study of the mesomorphic properties (by DSC, microscopic observation and X-ray diffraction) of three new series of semi-perfluorinated liquid crystals: 4-(2,2,3,3,4,4,4-heptafluorobutyloxycarbonyl)phenyl, 4-(2,2,3,3,4,4,5,5-octafluoropentyloxycarbonyl)phenyl, and 4-(3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluoro-octyloxy-carbonyl)phenyl 4-(n-alkyloxy)benzoates. One compound of the second family crystallizes in the P1 space group with Z ' 2. The molecule adopts a slightly bent conformation with a fully extended alkyloxy and semi-perfluorinated chain in a smectic C-like structure. The comparison of the present structure is made with that of a similar compound of the first family with a longer alkyloxy chain (this latter crystallizes in the P1 space group with two independent molecules in the unit cell). Comparison of the molecular packing shows the importance of the chain lengths in the molecular arrangement and molecular interactions in both structures.     

Invited Lecture. Smectic A polymorphism from low to high molar mass systems

The polymorphism of smectic A phases in low molecular weight (L.M.W.) liquid crystals is associated with strong anomalies in the period defining the layers. The smectic A phases of liquid-crystalline comb-like polymers also have various modes of spacing. However, the behaviour of these polymer phases shows some peculiarities compared with L.M.W. compounds, especially due to the main chain which takes part in the smectic arrangement. To specify further the S_A polymorphism in high molar mass systems, the use of side chain polymers with partial fixation appears to be very promising: either taking advantage of better compatibility and lower viscosity in order to describe binary diagrams with L.M.W. mesogens, or through the partial insertions of long polar side groups known to generate anomalies of periodicity as for L.M.W. compounds.     

Nematic disc-like liquid crystals

We present the first example of disc-like mesogens which present at high temperature a highly fluid mesophase with a nematic optical texture. These nematic disc-like compounds are pure simple component models to study the carbonaceous mesophase.     

The Existence of SA 1, SA d,SA 2 and S∼C Smectic Phases in the New Series 4-Alkoxyphenyl-4′- [4″-Cyanobenzyloxv] Benzoates

A homologous series of 4 - alkoxyphenyl-4′-[4″-cyano-benzyloxy] benzoates have been synthesized. Within this series three smectic A phases : S_{A 1}, S_{A d} and S_{A 2} were identified by mean of small angle X-Ray scattering. Furthermore three derivatives exhibit the novel smectic phase made of ribbons S～_C.     

Mesomorphic Properties of Di- (4 - Alkoxyphenyl) and Di- (4 - Alkanoyloxyphenyl) Tetrathiafulvalenes

The polymorphism of the di- (4 - alkoxyphenyl) and di- (4 - alkanoyloxyphenyl) tetrathiafulvalenes (TTF) is investigated. In the dialkoxy series, the short chain derivative exhibits a smectic G phase and a nematic phase. The latter phase disappears in the long chain derivative. The dialkanoyloxy derivatives exhibit a smectic G phase (for short chains) and a smectic C phase (for long chains). A plot of the mesormorphic-isotropic transition temperatures against the number of carbon atoms of the substituent shows the usual odd-even effect. Some tetra (alkoxyphenyl) tetrathiafulvalenes are described, unfortunately they have no mesomorphic properties.