Liquid Crystals
Liquid crystalline molecules are extensively used for technological applications such as liquid crystal displays, and there is a great deal of research underway in various fields exploring other uses. The carbon–carbon bond-forming cross-coupling reaction
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Liquid Crystals Ning-Hui Chang, Megumi Kinoshita and Yasushi Nishihara
Abstract Liquid crystalline molecules are extensively used for technological applications such as liquid crystal displays, and there is a great deal of research underway in various fields exploring other uses. The carbon–carbon bond-forming cross-coupling reactions can provide innovative synthetic methods for new liquid crystalline molecules with novel physical properties. Moreover, the organic molecules synthesized with the cross-coupling reactions may be used in new areas such as organic electroluminescence (EL) and thin film transistors (TFT).
Keywords Liquid crystals Nematic phases Smectic phases Organic devices Endotherms Calamitic
5.1 Introduction In 1888, Reinitzer discovered that cholesteryl benzoate had two melting points: it first melted into a turbid liquid with crystalline properties, and then at higher temperatures, it became clear [1]. Since then, a myriad of materials with liquid crystalline properties have been used in a wide variety of applications, including optical devices [2–7]. Research on liquid crystals is diverse, covering several
N.-H. Chang M. Kinoshita Y. Nishihara (&) Division of Earth, Life, and Molecular Sciences, Graduate School of Natural Science and Technology, Okayama University, 3-1-1 Tsushimanaka, Kita-ku, 700-8530, Okayama, Japan e-mail: [email protected]
Y. Nishihara (ed.), Applied Cross-Coupling Reactions, Lecture Notes in Chemistry 80, DOI: 10.1007/978-3-642-32368-3_5, Ó Springer-Verlag Berlin Heidelberg 2013
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scientific fields, such as chemistry, physics, and engineering. In the development of novel organic functional materials, liquid crystals often demonstrate substantial potential [8, 9]. With current technology, liquid crystalline compounds can be widely applied to a uniform and large display and can electrically control optical anisotropy, owing to their characteristic physical properties. Most liquid crystalline compounds used for displays must show the nematic phases. In order to apply the liquid crystals to optoelectronic materials, the temperature range showing the liquid crystal phases should encompass ambient temperatures. In general, liquid crystals have several common characteristics. They are polarizable molecules having a rigid core unit (rod-like or disc-like) with an extended p-electron system and one or more flexible ends. There are two important types of the most frequently utilized liquid crystalline materials with high dielectric anisotropy: analogs of 4-pentyl-40 -cyanobiphenyl (5CB) and analogs of fluorinated tolane (FT) liquid crystals, shown in Fig. 5.1. These mesogenic rigid biphenyl and diarylethene cores along with polar electron-withdrawing groups (a cyano or a fluoride group) at the edges offer the anisotropy necessary for the composition of the liquid crystal phase, whereas the alkyl chains contribute to a decrease in melting point [10]. Recent developments in this field have included the use of naphthalene and st
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