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Dimers discotic

S. Zamir, R. Poupko, Z. Luz, B. Huser, C. Boeffel, and H. Zimmermann, Molecular ordering and dynamics in the columnar mesophase of a new dimeric discotic liquid-crystal as studied by X-ray-diffraction and deuterium NMR, J. Am. Chem. Soc. 116 1973-1980 (1994). [Pg.88]

Figure 8.27 Stacking of two gold pyrazolate trimers into a discotic dimer of trimers. Figure 8.27 Stacking of two gold pyrazolate trimers into a discotic dimer of trimers.
The interest in the structures of simple R2Si(OH)2 compounds lies in the fact that one of them, Bu 2Si(OH)2, forms a discotic liquid crystalline phase (308,309). Despite many attempts, it has not proved possible to obtain crystals of Bu 2Si(OH)2 suitable for a crystallographic study, the material obtained from various solvents usually being of a fine fibrous nature. The discotic phase of Bu 2Si(OH)2 has been proposed (309) to be due to the formation of dimeric disks of molecules which remain on breaking the interdimer hydrogen bonds in a structure of type 65 at the transition between crystal and mesophase. As has been described, structure type 65 is found for several diols similar to Bu 2Si(OH)2, and it is thus quite likely that Bu 2Si(OH)2 does indeed have the proposed structure. [Pg.239]

Figure 7.39 (a) Schematic representation of discotic mesogens with only three alkoxy chains (n = 7, 8) (b) schematic representation of the star-shaped dimer. [Pg.424]

Figure 23 Synthesis of twin discotic dimer and branched oligomers from CTTV-7 mesogens connected with a hexadecane spacer. (From Ref. 76.)... Figure 23 Synthesis of twin discotic dimer and branched oligomers from CTTV-7 mesogens connected with a hexadecane spacer. (From Ref. 76.)...
Triphenylenes provided with nonionic di(ethylene oxide) side-chains (25f)132 134 or with ionic alkyl chains (25g)135 form supramolecular polymers in water.136 The arene—arene interactions of the aromatic cores allow for the formation of columnar micelles . At low concentrations the columns are relatively short, and the solutions are isotropic. At higher concentrations the longer columns interact and lyotropic mesophases are formed.133 Computer simulations showed that in the isotropic solution the polymerization of the discotics is driven by solute-solute attraction and follows the theory of isodesmic linear aggregation the association constants for dimerization, trimerization, and etc., are equal and the DP of the column thus can easily be tuned by concentration and temperature.137 138 At higher concentrations the sizes of the columns are influenced by their neighbors, the columns align, and the DP rises rapidly. [Pg.318]

A surprisingly efficient intermolecular photochemical [2 + 2] dimerization was achieved in the synthesis of belt-shaped cyclophanes by irradiation of arenoannelated [18]annulenes like 176 [116]. The highly selective threefold [27t+27t] cycloaddition yields dimers 177 in up to 68%. The efficiency of this dimerization process even at high dilution can be explained with the perfect preorganization of the discotic mesogenes 176. [Pg.130]

The synthesis of discotic, mercury-bridged, triphenylene dimers (166 R = OC5Hu, 0(CH2)2CHMe(CH2)3-CHMe2) was reported by Kumar et The bis(2,3,6,7,10-pentapentyloxy-triphenylene-l l-ethynyl)mercury(ll)... [Pg.287]

Pyridone forms a hydrogen-bonded dimer with a closed structure [136]. This dimerization has been used for the design of crystalline assemblies such as three-dimensional networks [136b]. This hydrogen bonding has been used for the formation of discotic liquid-crystalline assemblies [137]. Disk-like complex 58 with dodecyl chains displays a hexagonal columnar phase (Dh) between 88 and 108 °C. Columnar mesophases are also exhibited by benzamide dimers [138]. [Pg.127]

Non-Symmetric Discotic-Calamitic Liquid Crystal Dimers. 172... [Pg.149]

Fig. la-e. Sketches of the possible molecular architectures for liquid crystal dimers a symmetric calamitic dimer b non-symmetric calamitic dimer c symmetric discotic dimer d non-symmetric discotic-calamitic dimer e laterally linked symmetric dimer. Ellipses represent rod-like mesogenic groups, circles disc-like mesogenic units and wavy lines denote the flexible spacers... [Pg.152]

There are relatively few reports of liquid crystal dimers containing discotic mesogenic units [105-112] and this has been due in large part to the difficulties in preparing monofunctionalised discotic precursors. Without such monofunctional precursors the preparation of discotic dimers often involves laborious separation procedures involving several isomers of the discotic core. In recent years, however, there have been many advances in the synthesis of triphenylene-... [Pg.170]

Discotic dimers have a strong tendency to exhibit columnar phases but an example of a nematogenic discotic dimer has been reported by Praefcke et al, which was based on two discotic multiaUcylnyl units [111],... [Pg.171]

The existence of the thermotropic biaxial nematic phase was theoretically predicted almost thirty years ago [119] but such a phase has yet to be unambiguously identified. Indeed, as we saw in the previous section, a biaxial nematic phase has been claimed for a class of discotic dimers [111], Theory predicts that mixtures of rod-like and disc-like molecules should exhibit the biaxial nematic phase [120] but experimentally such systems phase separate... [Pg.172]

This experimental difficulty was overcome by simulating the behaviour of a model system and a biaxial nematic phase was indeed obtained [122], One way by which the problem of phase separation could be solved experimentally was suggested by Fletcher and Luckhurst and involved covalently linking a rod-like and disc-like unit via a flexible spacer yielding a non-symmetric discotic-calamitic liquid crystal dimer [123] ... [Pg.172]

Fig. 7.34 (a) Shish-kebab conducting polymers L-L = 4,4 -bipyridine or pyrazine. (b) Porphyrin co-facial dimers and possible discotic array of metal-metal bonding causing conduction. [From Collman et al. 1990.]... [Pg.239]

Complex with discotic shapes can be obtained by the association of hydrogen bond between identical molecules [51, 52]. Disklike dimer 36 [51 ] and trimer 37 [52] can exhibit thermally stable columnar phase up to around 200 °C as a result of stable hydrogen bonding formation and k-k stacking. [Pg.142]

The monofunctional P-U complex (supermolecule 19, Table 3) has been shown to form disklike dimers that can self-assemble into columns displaying thermotropic behavior. Each disk has a thickness/diameter ratio of 0.1 [155], The formation of columnar mesophases by similar discotic supermolecules is described in the previous section when cases in which liquid crystallinity and growth are hierarchically related, coupled, or totally uncoupled were considered. Lack of data on the equilibrium constants, or DP, prevents a definite assessment of the assembling mechanism of discotics based on supermolecule 19. [Pg.75]


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See also in sourсe #XX -- [ Pg.2 ]

See also in sourсe #XX -- [ Pg.2 ]

See also in sourсe #XX -- [ Pg.38 , Pg.39 ]




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Calamitic-discotic dimers

Discotics

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