Conductivity 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. 

As discussed in Chaps. 3 and 4, (columnar) discotic liquid crystals are oriented in columns separated by molten aliphatic chains and, consequently, they can conduct charge efficiently along the channels in one dimension. The organization of the different phases is described elsewhere [19, 20] and the efficiency of charge transport can be directly related to the short intermolecular spacing and order of different types of mesophase, with few exceptions [21]. For example, hole mobility is higher in ordered, rather than disordered, columnar phases and even higher in helically-ordered phases where molecular rotation is suppressed about the columnar axis [22], Some mesomorphic derivatives of hexabenzocoronene, for example hexaphenyl-substituted hexabenzocoronene (HBCn, see Table 8.2 for chemical structures of all discotic materials discussed here) have hole mobilities... 

Several mixtures of hexanethiol capped gold nanopartides and triphenylene based discotic LCs have been studied. These mixtures display liquid crystal behavior (columnar mesophases) and an enhancement in the DC conductivity, due to the inclusion of gold nanoparticies into the matrix of the organic LC [70]. Other studies of mixtures of gold nanoparticies with mesogens indude a series of cholesteryl phenoxy alkanoates. The inclusion of the nanopartides does not change the inherent liquid crystal properties of the cholesteryl derivative but the mesophases are thermally stabilized [71]. 

Extensive studies have been conducted to investigate the formation of chiral columns or helical superstructures in chiral and nonchiral disk- [53], star- [54, 55], and board-shaped [56] molecules. However, spontaneous deracemization has never been unambiguously demonstrated in discotic columnar phases consisting of nonchiral or racemic molecules. We recently observed clear evidence showing chiral resolution in a disk-like molecules with a dibenzo[g,p]chrysene core [57]. 

In Fig. 8 is shown a semi-logarithmic plot of the /e decay time of the conductivity transients, T, against the disc diameter for several discotic phthalocyanine and HBC derivatives. The good agreement with the straight line drawn through the data illustrates the exponential dependence of the decay of the conductivity on the inter-columnar distance, i.e. = T (0)exp /3R. The process respon-... 

In general, for side chain liquid-crystalline polymers, macroscopic molecular alignment is not easy and therefore clear evidence of electronic charge carrier transport was confirmed first in liquid crystals with low molecular weight. In the 1990s, fast electronic conduction was verified in discotic columnar phases of triphenylene derivatives [79,80] and hexabenzocoronene derivatives [81,82] as well as smectic phases of 2-phenylbenzothiazole [83, 84] and 2-phenylnaphthalene derivatives [85], as shown in Fig. 14. Carrier... 

Carslaw HS, Jaeger JC (1946) Conduction of heat in solids. Clarendon, Oxford Cerclier CV, Ndao M, Busselez R, Lefort R, Grelet E, Huber P, Kityk AV, Noirez L, Schonhals A, Morineau D (2012) Stmcture and phase behavior of a discotic columnar liquid crystal confined in nanochannels. J Phys Chem C 116(35) 18990-18998 Cussler EL (2009) Diffusion mass transfer in fluid systems, 3rd edn. Cambridge University Press, Cambridge... 

Fig. 2.13 Intra-columnar mobility in the hexagonal columnar phases (Db) of various discotic materials. The n indicates the number of carbon atoms in a discotic core of the materials. The mobility was determined by pulsed radiolysis transient microwave conductivity (PR-TRMC) measurements...

---