Columnar mesophase liquid

Thermotropic liquid-crystalline properties of different metal alkanesulfonates are studied by microscopy and X-ray diffraction [59]. Sodium soaps show smectic polymorphism of smectic A and smectic B phases. Ammonium soaps only show smectic A phases but polymorphism in the crystalline state. Calcium soaps show columnar mesophases. In Figs. 32 and 33 some textures and x-ray diffraction patterns are depicted. 

The prime requirement for the formation of a thermotropic liquid crystal is an anisotropy in the molecular shape. It is to be expected, therefore, that disc-like molecules as well as rod-like molecules should exhibit liquid crystal behaviour. Indeed this possibility was appreciated many years ago by Vorlander [56] although it was not until relatively recently that the first examples of discotic liquid crystals were reported by Chandrasekhar et al. [57]. It is now recognised that discotic molecules can form a variety of columnar mesophases as well as nematic and chiral nematic phases [58]. 

Several mixtures of hexanethiol capped gold nanopartides and triphenylene based discotic LCs have been studied. These mixtures display liquid crystal behavior (columnar mesophases) and an enhancement in the DC conductivity, due to the inclusion of gold nanoparticies into the matrix of the organic LC [70]. Other studies of mixtures of gold nanoparticies with mesogens indude a series of cholesteryl phenoxy alkanoates. The inclusion of the nanopartides does not change the inherent liquid crystal properties of the cholesteryl derivative but the mesophases are thermally stabilized [71]. 

Benouazzane, M., Coco, S., EspineL P., Martm-Alvarez, J. and Barbera J. (2002) Liquid crystalline behavior in gold(I) and silver(I) ionic isocyanide complexes smectic and columnar mesophases. Journal of Materials Chemistry, 12, 691-696. 

Trzaska and co-workers showed a similar propeller mechanism for the formation of helical columns from disclike metallomesogens (29-31).34 These metallomesogens also have C3 symmetry and 30 and 31 are provided with chiral side chains. In the hexagonal columnar mesophase these chiral side chains induce a Cotton effect in the chromophore of the helically arranged core. Heating the mesophase to the isotropic liquid results in the disappearance of the Cotton effect because of the loss of helical order. This effect illustrates the need for the molecules to be positionally ordered in order for the side-chain chirality to be transferred to the supramolecular column. 

Nuckolls and Katz have synthesized discotic liquid crystalline molecules in which the core is a helix in its own right.37 Nonracemic helicene 33 was found to assemble into a columnar mesophase in which the helicenes stack on top of each other. CD spectroscopy showed a strong increase of the Cotton effect upon going from the molecularly dissolved state to the aggregated state, exhibiting an amplification of chirality. These helical columns give rise to a strong expression of chirality because the intrinsic shape of the helicenes... 

Discotic liquid crystals arise from disk-shaped molecules as nematic or cholesteric mesophases. Their structural characteristics are similar to the respective ealamitie mesophases, that is, the normals of the disks are oriented parallel. Instead of the smectic mesophases, diseotie columnar liquid crystals arise from eonnecting the disks to each other. The columns of the discotic columnar mesophase form a two-dimensional lattice whieh is in a hexagonal or rectangular modification. In addition, the columns may be tilted (Fig. 2f,g). 

Columnar mesophase characterised by a liquid-like molecular order along the columns, in which the columns are arranged in a rectangular packing. 

Keywords Columnar mesophase Cubic mesophase Dendrimer Liquid crystal Metallomesogen Micro-segregation Organic semiconductor Perfluorinated molecule Polyphilic molecule Self-assembly... 

Lattermann found that the sixfold symmetry is not important for the presence of columnar mesophases in [14]-N4 when appropriate peripheral groups are chosen [105]. As substituents with one terminal alkyl (88a-d) chain and with three terminal alkyl chains (88e) are not able to induce liquid crystalline behavior in 88 (Table 5) [104], a substituent with two alkyl chains, namely 3,4-bis(alkyloxy) benzoyl, was chosen since it has been known to induce liquid crystalline phases in other systems. A mesophase (most likely Colh due to the texture) was observed between 96 and 132 °C for 90 (Scheme 44). 

The most comprehensive studies on shape-persistent Hekates have been performed on stilbenoid star-shaped molecules. Structures and mesomorphic properties are collected in Table 1. Core building blocks with only one repeating unit per arm and one flexible chain 26a,b, 28a-d, 30a did not show any liquid crystal properties [56-58]. In the series of two chain derivatives 28e, 30b,c the formation of meso-phases depend on the core [57-59]. The electron deficient triazine and the dicyanopyridine building block induced obviously columnar mesophases. The pyridine derivative 30b showed only a crystalline phase [58]. In the series of nine chain stars 26c-g [60-62] and 28f-n [57], the compounds formed columnar phases depending on the chain length of the peripheral chains. Propyloxy chains are too short but hexyloxy and dodecyloxy chains are sufficient for the formation of liquid crystal phases by nanosegregation [60-62]. This can be rationalised by a dense... 

The recent description of the construction of a solid state photocell [145] based on order attained via a columnar mesophase of a liquid crystalline porphyrin [146] represents one application of photoinduced electron transfer within organized media which may prove to be fruitful in the future in the burgeoning area of molecular electronics. 

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