Discotic polymeric mesogens

Figure 14.26 Discotic polymeric mesogens (a) columnar hexagonal (b) sandic nematic.

Subsequent intramolecular oxidative coupling with either vanadium(V) oxyfluo-ride/boron trifluoride diethyl ether etherate or thallmm(III) oxide/trifluoracetic acid resulted in the corresponding phenanthrene-9,10-diones 1259. It has been shown that oxygen functionalities at the 3-, 3 -, 4-, and 4 -positions are necessary for coupling to occur. These substituted benzils and phenanthrene-9,10-diones constitute precursors for ligands in the field of discotic metallomesogens or polymeric mesogens. 

Most polymeric Hquid crystals are based on stiff rod-like molecular units which are called calamitic mesogens. There are some unusual polymers (which are not discussed here) that contain flat disk-like molecular units called discotic mesogens in which the disks form columnar arrays like stacks of poker chips. 

Discotic SCLCPs were synthesized by the group of Grubbs [82]. For this purpose, norbornenes XXVIII-n (n=5, 10) and cyclobutenes XXIX-n (n=5, 10) with alkoxy-substituted triphenylenes as mesogenic units (see Fig. 18) were prepared. Polymerization was carried out with initiator 6. The resulting polymers had a narrow PDI between 1.09 and 1.17. Physico-chemical data for poly-XXVIII and poly-XXIX are listed in Table 18. 

Thermotropic Liquid Crystals. - Organic molecules, having aromatic rings or unsaturations thus producing elongated shapes, and also polymeric molecules often show thermotropic phase behavior. Mesomorphism comprises typically nematic, smectic A and B, and cholesteric thermotropic phases, but in several cases columnar, discotic and rod-disk self-assembly shapes of thermosensitive mesogens have been observed. 

Substances that show a liquid crystalline phase, or mesophase, are called mesogens. Several thousands of compounds, both with low molecular mass and polymeric, are now known to form mesophases. They are mainly highly geometrically anisotropic in shape, rodlike or disclike (hence the terms calamitic and discotic liquid crystals), or they are anisotropic in solubility properties, like amphiphilic molecules and, depending on their detailed molecular structure, they can exhibit one or more mesophases between the crystalline solid and the isotropic liquid. Transitions to these intermediate states may be induced by purely thermal processes (thermotropic liquid crystals) or by the action of solvents (lyotropic liquid crystals). Each of these two categories can be further divided according to the structure of the mesophases and/or molecules Scheme 1 shows the classification of thermotropic mesophases. 

As indicated in Figure 8, the crosslinking of discotic monomers might lead to insulated wires. The crosslinking of diacetylene-functionalized mesogens via a topochemical polymerization in a columnar phase was reported, but no electronical charartetization was performed. ... 

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