Discotic liquid crystalline

Yamada, M., Shen, Z. and Miyake, M. (2006) Self-assembly of discotic liquid crystalline molecule-modified gold nanopartides control of ID and hexagonal ordering induced by solvent polarity. Chemical Communications, (24), 2569-2571. 

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. 

Considerably less work has been done on discotic liquid-crystalline elastomers [189,190] and cholesteric elastomers [191]. The same seems to be true for smectic elastomers [192,193], even though some of them have the additional interesting property of being chiral [194,195]. 

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... 

The authors like to express their warm thanks to the many co-workers from our laboratories and our collaborators who participated in the work reported here for their enthusiasm to be actively involved in the field of chiral discotic liquid crystalline materials. Also the continuing discussions to unravel the many features of these systems are highly acknowledged. Their names appear in the list of references. 

Nanoscale discotic liquid crystalline porphyrins, (I), were prepared by Li et al. 

Just as chiral induction can be realised in discotic liquid crystals, it can also be realised in assemblies of disc-like molecules or disc-like aggregates. As far as molecules are concerned, C3-symmetrical trisamides (Fig. 15), which actually exhibit discotic liquid crystalline phases, also form chiral columnar stacks through it-it interactions when dissolved in apolar solvents, which are depicted schematically in Fig. 15 [121]. An achiral compound of this type (15) exhibits no optical activity in dodecane, but when the compound is dissolved in the chiral CR)-(-)-2,6-dimelhyloctanc significant Cotton effects (only slightly less intense than those observed in a chiral derivative) are detected. The chiral disc-like trisamide 16 can also be used as a dopant at concentrations as low as 2.5% to induce supramolecular chirality in the stacks of achiral compound. In this case, the presence of the additional hydrogen... 

Figure 6.12 Macrocycles 137-142 exhibit inverted discotic liquid crystalline properties. Inset crystal structure of 138 [110]. Reprinted with permission from S. Hoger, X. H. Cheng, A.-D. Ramminger, V. Enkelmann, A. Rapp, M. Mondeshki, I. Schnell, Angew. Chem. Int. Ed. 2005, 44, 2801-2805.

Recent work focuses on non-classical mesogenes which are built up by self-assembly. One example is a family of polymers containing disk-like groups which form no liquid crystalline phase, but ean act as an electron acceptor or donor. Charge transfer complexation with a complementary low molecular mass compound induces nematic or columnar discotic liquid crystalline order [153,154]. Figure 13 demonstrates this with the example of a polyester, bearing electron-rich tetra(alkoxy)tri-phenylene-units in the main chain, mixed with the electron deficient aromatic 2,4,7-trinitro-9-fluorenone (TNF). While the pure polymer shows a non-ordered isotropic melt, a columnar phase appears on addition of TNF. 

Warman JM, Kroeze JE, Schouten PG, van de Craats AM. (2003) Charge mobility in discotic liquid crystalline porphyrins and phthalocyanines measiared by PR-TRMC. J Porphyrins and Phthalocyanines 7 341-349. 

Magnetically Aligned Discotic Liquid-Crystalline Semiconductors, J. Am. Chem. Soc. 127, 16233, 2005. 

Shklyarevskiy, 1.0. et al.. High anisotropy of the field-effect transistor mobihty in magnetically aligned discotic liquid-crystalline semiconductors, J. Am. Chem. Soc. ni, 16233-16237, 2005. 

Star-shaped compounds having a 1,3,5-triazine core and stilbenoid arms have been prepared. These compounds form nematic discotic systems <04T6881>. Discotic liquid crystalline... 

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]. 

Just as chiral induction can be realized in discotic liquid crystals, so it can in assemblies of disc-like molecules or disc-like aggregates. As far as molecules are concerned, C3-symmetrical fm-amides (Fig. 6), which exhibit discotic liquid-crystalline phases, also form chiral columnar stacks through n-n interactions when dissolved in apolar solvents,which are depicted schematically in... 

Novel nanoscale discotic liquid crystalline porphyrins 14 with partial alkyl chain perfluorination has been designed and synthesized in our group which exhibits exceptionally enhanced tendency to spontaneously self-assemble into homeotropically ordered nanostructures [107]. The defect-free homeotropically aligned fluorinated porphyrin thin films were fabricated and characterized. In the films thinner than 10 pm in glass cells, it shows strong tendency towards homeotropic... 

T.S. Perova, J.K. Vij, The influence of surface stnicture on the discotic liquid crystalline alignment an in ared spectroscopy study. Adv. Mater. 7, 919-922 (1995)... 

V.D. Cupere, J. Tant, P. Viville, R. Lazzaroni, W. Osikowicz, W.R. Salaneck, Y.H. Geerts, Effect of interface on the alignment of a discotic liquid crystalline phthalocyanine. Langmuir 22, 7798-7806 (2006)... 

D. Miyajima, F. Araoka, H. Takezoe, J. Kim, K. Kato, M. Takata, T. Aida, Electric-field-responsive handle for large-area orientation of discotic liquid-crystalline molecules in millimeter-thick films. Angew. Chem. Int. Ed. 50, 7865-7869 (2011)... 

A.M. van de Craats, N. Stutzmann, O. Bunk, M.M. Nielsen, M. Watson, K. Mullen, H.D. Chanzy, H. Sirringhaus, R.H. Friend, Meso-epitaxial solution-growth of self-organizing discotic liquid-crystalline semiconductors. Adv. Mater. 15, 495-499 (2003)... 

A. Angelova, J. Reiche, R. Ionov, D. Janietz, L. Brehmer, Control of the structure of Langmuir-Blodget films of a discotic liquid crystalline compound via the subphase composition and the adjacent molecular environment. Thin Solid Films 242, 289—294... 

H. Schonherr, F.J.B. Kremer, S. Kumar, J.A. Rego, H. Wolf, H. Ringsdorf, M. Jaschke, FL-J. Butt, E. Bamberg, Self-assembled monolayers of discotic liquid crystalline thioethers, discoid disulphides and thiols on gold molecular engineering of ordered surfaces. J. Am. Chem. Soc. 118, 13051-13057 (1996)... 

Here in this chapter, studies on molecular blends of liquid crystalline materials, especially discotic liquid crystalline blends as semiconductor are overviewed in terms of both macroscopic miscibility and nanoscopic phase separation. Discotic liquid crystal has been extensively studied as one-dimentional semiconducting materials in recent years [12-14]. In particular, organic thin film photovoltaics is an interesting research field of its application. We see blended molecular systems... 

Therefore, miscibility in discotic columnar mesophase is recognized as a result of molecularly dispersed systems. However, we should pay some attention to a state of mixture for two discogens to form the identical columnar mesophase. As a more realistic system, is it a molecularly dispersed or a single-component column dispersed system This is an essentially important question when we consider the application of discotic liquid crystalline blends as a new tool for organic electronic materials (Fig. 8.4). 

Unfortunately, not so many experimental evidences and theoretical studies have been reported so far. Especially, compounds provided for the studies on binary systems as a semiconductor and its related devices do not show so much variation. In the next sections, we overview the research results on discotic liquid crystalline blends for semiconducting materials and for organic thin film photovoltaics. 

Discotic Liquid Crystalline Blends CaHjO OC4H0... 

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