Mesophase formation compounds

Lewis and Singer (17) overview the role and importance of stable free radicals in carbonization processes. Fitzer et al (18) provide a comprehensive description of the chemistry involved in the conversion of specific organic compounds to carbon. Marsh (19-23) and Forrest and Marsh (24) relate the chemistry of mesophase formation to its properties and applications. The journal CARBON published an issue devoted specially to studies of mesophase and its applications (25). The world availability of pitch materials is such that there is an abundance of pitch which produces cokes of little industrial value. 

Serrano and co-workers have reported the synthesis of two interesting series of chiral, hexacatenar metal complexes, that is, mono- and dinuclear, derived from chiral oxazoline-based ligands.None of the pure dinuclear compounds (136 X = OAc, Cl) was mesomorphic and most were room-temperature oils or glassy materials. This is likely due to the sterically demanding central chiral unit preventing molecular stacking and, hence, mesophase formation. 

It first proved that a cisoid conformation (U-shape) does not prevent mesophase formation, but also that this type of structure can lead to potentially ferroelectric materials, since compound 58 was obtained as a mixture of isomers, some of them being optically active (planar chirality). 

Smith, G. W. "Phase Behavior of Some Condensed Polycyclic Aromatics", Mol. Cryst. Liq. Cryst., Vol. 64, Letts., pp. 15-17. Chen, S. H. Diefendorf, R. J. "Mesophase Formation in Polynuclear Aromatic Compounds , Extended Abstracts, 16th Biennial Conf. on Carbon, U.C. San Diego, July, 1983, pp. 28. 

The mesophase microstructure was examined using polarized light microscopy. It was found that organic sulfur compounds have less effect on mesophase microstructure than elemental sulfur but some organometallic compounds greatly inhibit mesophase formation. 

The influence of organic enlfnr (M by weight) with organometallic compounds on mesophase formation in Cat. Inc. asphaltene. 

Oi S. and Onishi N. Influence of Organic Sulfur Compounds and Metals on Mesophase Formation Carbon 1978 16 455. 

A series of related metallaazaporphyrins has been studied which differ from the previous examples by the structure of the peripheral chains, which are alkenylsulfanyl groups ((31) M = 2H, Ni, Co, Cu, R = C H2 i, n = 4-6, 7, 8). Thus, the presence of a terminal double bond in the peripheral chains did not preclude mesophase formation, as all the metal complexes exhibited mesomorphism, in addition to the free-base compounds with n = 4 and 5 (Figure 31). Overall, the presence of the terminal double bond reduced the thermal range of the mesophase. 

Due to the important role of chirality in liquid crystals, a large number and variety of chiral chemical compounds have been developed. This chapter describes the most important molecular fragments and classes of chemical structures (Section 4.2) which provide both chirality and mesogenic properties. The form of chiral phases depends on the principles of the mesophase formation (Section 4.3). Some relations between the molecular chirality and the appearance of mesophase chirality are discussed and chiral dopants are classified (Section 4.4). With respect to the mesophase behavior and to optical and electro-optical applications, it is important to know how the mesogenic chirality can be modified, e.g., chemically by photoisomerization, or by changes of temperature or composition for certain suitable compounds (Section 4.5). Finally, chiral liquid crystals provide not only optical and electro-optical applications but also applications in Chemistry, e.g., as chiral solvents for synthesis, chiral stationary phases in chromatography, or chemical sensors (Section 4.6). 

The term mesogenic means that the structure is generally compatible with mesophase formation. A compound that forms real mesophases is however mesomorphic. 

The geometrical anisotropy of mesogenic compounds is certainly their most obvious common feature. Since lateral attractions play an important role in mesophase formation and stability, the effect of molecular breadth has been studied rather extensively. Generally, smectic states suffer more from molecular broadening than do nematics. 

Table 1 Influence of spacer and side chain on mesophase formation in compounds 67 (Fig. 18). ...

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