Stilbazoles liquid crystals

Another approach to get new liquid crystals is the lateral fluorination of the stilbazole ligands,337 which is a common and highly effective tool to exert control over mesomorphism, crystal phase stability, and physical properties. Other modifications include the use of more alkoxy substituents and other alkyl sulfate anions.338-344 Ionic silver amino complexes also display liquid crystalline behavior at rather low temperatures they are of the form [Ag(NH2 -CJl +OJX (X = N03, n = 6,8,10,12,14 X = BF4, = 8,10,12,14).345... 

B. Langmuir-Blodgett Films of Metal Stilbazole Complexes Liquid Crystals... 

The greatest amount of work we have carried out with alkoxystil-bazoles is in the field of liquid crystals indeed, this is where our interest in stilbazoles started. After a brief and rather general introduction to liquid crystals, we will consider various types of complex that form liquid-crystal mesophases when complexed to stilbazoles, emphasizing patterns of behavior without delving into the subtleties. A more detailed discussion of the silver systems may be found elsewhere 24). Finally, although this article appears in a series that concentrates on inorganic chemistry, we offer an overview of some of our work with stilbazoles in hydrogen-bonded liquid crystals. 

The stilbazole complexes of these metals, Pd(II), Pt(II), Ag(I), and Au(I), are considered together because a good deal can be learned by looking at them in this way, particularly as we begin to look at more highly substituted stilbazoles. The liquid-crystal aspects of the silver... 

Having synthesized a number of complexes of monoalkoxystilbazoles, we explored the effect of using various poly(alkoxy)stilbazoles, given the interesting mesomorphism found in polycatenar mesogens (Section VI,A,3). This work is discussed in detail elsewhere 24). Here, we give an overview of the work to enable the reader to see the overall pattern of liquid-crystal behavior and the issues that arise. 

Hydrogen bonding was used to prepare supramolecular ferrocene-containing liquid crystals. The latter were obtained by associating an Fc derivative carrying a carboxylic acid function with either 4,4 -bipyridine 62 or stilbazole derivatives 63 (m, n) " Tetracatenar derivative 62 gave rise to a Colh phase from 66 to 72 °C. The... 

Two homologs of 78a (M = Pt, X = Cl, = 4, 6) were investigated in the formation of LB fdms. "" It was found that better fdms were obtained with the homolog that was mesomorphic at room temperature (n = 6). In the absence of more data, it is difficult to know how strongly this is correlated with the ambient liquid-crystal behavior of the material, or whether it results from a much lower degree of amphipathy due to the shorter chains. For example, well-ordered LB films of Ir(l) stilbazoles (71, see Section X.11.2) have been formed where the mesophase of the complex is found above 85 °C. 

Both hydrogen bonding and halogen bonding can be used to realize new liquid crystals. Bruce and coworker have first reported that complex 22-n formed by a 4-alkoxy stilbazole and iodopentafluorobenzene showed SmA phases with a mesophase range from 81 to 84 °C. Recently, they also reported trimeric new liquid... 

Koh, K. N., Araki, K., Komoii, T., Shinkai, S. (1995), Thermotropic liquid-crystal construction through the hydrogen-bonds between a stilbazole calix[4]arene and carboxylic-acids. Tetrahedron Letters, 36, 5191-4. 

The 4 -alkyloxy-4 stilbazoles (n-OST) 6, are 4-substituted pyridines and have been widely used by the Sheffield liquid crystal... 

Iridium complexes of dimeric stilbazole, 9, have been synthesized recently. These materials show a very laige odd-even effect in their melting behavior, and are called metal-containing Siamese Twin liquid crystals [18]. 

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