Discotic monomers

Also, the chemistry and polymerization of discotic monomers has been reviewed [10]. Their current and emerging uses are in optical compensation films for liquid crystal displays, carbon nanostructures, organic electronics, solar cells, light-emitting diodes, and field-effect transistors. 

The starting compound for discotic monomers is hexahydroxytriphenylene. Suitable compounds bearing acrylic units are attached to the hydroxy groups [35]. In general, discotic liquid crystal compounds exhibit a large refractive index of birefringence. This means that the material is highly anisotropic. 

Figure 6 Schematic representation of two types of isodesmic growth (a) supramolecular polymerization of a rigid discotic monomer into a linear SP and (b) supramolecular polymerization of a bifunctional monomer bearing two binding groups connected by a spacer. The association constant for each iterative addition of monomer to the growing polymer chain is defined as the ratio of the rate constants of association to dissociation /fa = /fi//Ci).

An alternative should be the synthesis of discotic monomers with only tetra or trisubstituted central cores. 

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. ... 

Fig. 18 Chemical structures of monomers with discotic mesogens...

Monomers with reactive groups such as acrylic and cyclic ether units are used in the fabrication of liquid crystalline displays (LCD)s. A monomer with acrylic units is shown in Figures 16.4 and 16.4. A discotic photopoly-merizahle liquid crystal monomer is shown in Figure 16.4. 

S. Kumar, Chemistry of Discotic Liquid Crystals From Monomers to Polymers The Liquid Crystals Book Series (CRC Press, Boca Raton, 2011)... 

Kumar S. Chemistry of discotic liquid crystals from monomers to polymers. Liquid crystals book series. Boca Raton, FL CRC Press 2011. ISBN 9781439811436. 

The vast range of supramolecular polymeric materials also extends from the use of small molecules (e.g., double-sided discotics or multifunctional monomers with a discrete tether) to very large molecules (polymeric or dendritic). Another important characteristic of SPs is the timescale upon which the chains exist, which is defined by the rate of association/ dissociation of the monomers. Tme dynamic SPs must be reversible (breaking and recombining) on experimental time-scales (e.g., NMR timescale). A physical model developed by Cates and co-workers predias many viscoelastic properties of SPs as a funaion of the strength of the noncovalent interactions existing between monomers.Although initial studies focused on wormlike micelles, the model has been demonstrated to successfully describe the viscosity behavior of reversible, self-complementary UPy-based SPs. ... 

Koerner et al. reported that cyanate ester monomer Cl and C3 could be oriented and polymerized in an a-c electric field [39] and that the orientation of the molecules was controllable by changing the frequency of the field. The cyanate ester LC monomer could self-organize in such a dynamic environment. This orientation-on-demand technique will provide a new method to control and modify high performance materials. It is claimed that triazine systems based on 2,4,6-tris[4-aminophenyl)-alkoxybenzylidene]-l,3,5-triazine form a discotic liquid crystalline phase [50]. This report made the investigation of such networks of even more interest. 

It seems to be important for the synthesis of discotic liquid crystalline polymers to find simple and clear synthetic pathways for related monomers. 

The controlled synthesis of discotic polymers requires a functionalized tristar-discogen-monomer. The described reaction of 3,4,5-tris(alkoxy)benzoic acid chloride with protected cis,cis-phloroglucit and the subsequent deprotection leads to a first key-compound in this synthetic pathway the diol-compound 4, member of a novel class of discotic associates. A controlled functionalization of the 3,4,5-tris(alkoxy)derivatives should lead to the second key-compound in the stepwise synthesis of discotic polymers. 

Rgureie Diagram of states of the C3 discotic of Figure 13 in the solvent n-butanol. The symbols represent data obtained by various experimental methods, and the lines the theoretical fits to the experimental data [75]. At low concentrations of material the monomers polymerize directly into helical polymers, while at higher concentrations a nonhelical polymerized regime intervenes. The demarcation of the monomeric and the polymeric regimes is set at 50% fraction material in polymers, rt= and that between the helical and nonhelical states by a 50% fraction of helical bonds, 0 =. ... 

We end this chapter with a very brief account of a new class of liquid crystal polymers, i.e. discotic polymers [118-126]. The basic monomer units are discotic mesogen-ic moieties, which are components of the polymer main chain itself or are attached to the polymer backbone as side groups. A few examples are shown as structures 14-16. Besides the columnar phase, some new types of mesophase have been identified. A... 

TNF-CT complexes of 2,3,6,7,10,11-hexakispentyloxytriphenylene or related amphiphilic derivatives are also able to form Langmuir-Blodgett (LB) films [57]. Polarized UV/VIS and infrared spectra of those of TNF complexes of hexakisalkyloxytri-phenylenes discussed here, for example, indicate a preferred orientation of the columnar axes parallel to the surface and to the dipping direction [57 a]. An amphiphilic triphenylene derivative with a pair of co-OH chains and four pentyloxy groups, forming a lamellar mesophase in the neat state, a nematic discotic main chain polymer derived from the aforementioned monomer both exhibit induced columnar hexagonal (Col j,) mesophases with TNF in the bulk state [57b]. The X-ray diffraction pattern of the... 

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