Electrical columnar discotics

Other liquid crystal phases composed of molecules having unusual molecular shapes are also known. Some compounds form a cone or bowl shape. These materials are often referred to as bowlic, and some typical examples are hexasubstituted tribenzocyclonones and aza-crowns (17), molecules of which stack on top of each other to form an ordered column which may have anomalous electrical conductivity. When a disklike molecule is divided by a rod-shaped spacer, the molecule (18) is referred to as a phasmid. It exhibits phases bearing some resemblance to columnar discotics. 

This book does not intend to cover the whole field of thermotropic liquid crystalline (TLC) materials as it is extremely difficult to cover within a single book. Instead it presents a collection of Chapters written by experts on various exciting topics in the field. Properties of recently developed TLCs (such as banana-type, thiophene-based, and columnar TLCs), phase biaxiaUty, and novel polymeric TLCs are discussed In detail. Solid-state NMR studies to obtain atomistic-level structural and geometrical information of TLCs are presented. Synthesis of liquid crystalUne conjugated polymers, fast switching of nematic materials by an electric field, and photoconducting discotic systems are also presented. 

Charge carrier transport in mesophases is quite unique compared to that in amorphous and crystalline materials. The mobility hardly depends on temperature at room temperature and above as shown in Fig. 2.6. Furthermore, it hardly depends on electric field either, as shown in Fig. 2.7. This behavior is not limited to one particular class of liquid crystals, but is probably a general characteristic of charge carrier transport in mesophases above room temperature. In fact, this behavior is also found in discotic columnar mesophases [11, 39,40,42]. 

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