Linking substituted mesogens

Any increase of polarity of the hydrocarbon, for example by substitution with chlorine or by replacing CH2 groups by ether oxygens, also increases incompatibility with perfluoroalkanes as polar interactions become more important [89, 96]. Polar groups are fundamental constituents of the mesogenic cores, especially as linking units and as substituents at aromatic moieties, and these groups increase the incompatibility between the aromatic cores and Rp-chains. 

With trimeric supermolecular materials the situation becomes more complicated because not only are there linearly and laterally linked possible structures, but also there are structures where the mesogenic units could be linked to a central point, creating a molecular knot . In a similar way, tetra-, penta-, etc., substituted supermolecules can be created. 

In fused twins the two mesogenic moieties are linked rigidly. Four-fold substituted ring systems (e.g. 17 [216]) can belong to this class. Induced in the research in this area are... 

Recently, Hoffmann et al. [12] have described the molecular and crystalline solid structure of 2-n-nonyl-1,4-phenylene bis(4-n-octyloxybenzoate), as estimated using X-ray diffraction [12]. The observed structure deviates from the model for the nematic phase in the crystalline solid state, as the lateral chains exist in -trans conformation. The type of link between the lateral hydrocarbon chain and the mesogenic core influences the course of the clearing points. A comparison performed for the 2-alkyl, acyl and alkyloxycarbonyl substituted derivatives 2a-2c in Table 1 showed a break in the clearing-point curve at 2b and 2c for five single units (including the -CO- or -CO-0 groups) within the lateral chains. The lower the transition temperatures the more pronounced the break in the curve [13, 15]. 

Other examples of functionalized monomers are polyoxyethylene (POE) chains linked to the thiirane with monothioacetal or ester functions (macromonomers), POE chains containing a thiirane group at both chain ends (bis-macromonomer), and stilbene mesogen and other side chain liquid crystalline-substituted thiiranes. ... 

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