Triphenylene derivatives, discotics

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]. 

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... 

Ordered thin layers can also been obtained from dilute solutions of discotic compounds onto gold or silicon surfaces. For example, triphenylene derivatives with a single long (o-alkylthiol chain have been shown to self-assemble into monolayers, in which the two types of orientation, face-on and... 

Complexes of polymeric acceptors and monomeric donors are also effective in inducing discotic PLCs. This was shown, in particular, for a main chain polyester into which TNF was incorporated, mixed with a triphenylene derivative [73]. In order to avoid phase separation, the donor concentration must exceed the acceptor concentration by a mole ratio of at least 3 1. It was also demonstrated that the alkyl spacer length in the main chain can be critical to the definition and stability of the discotic mesophase obtained. As illustrated in Figure 3.32, spacer lengths which are either too short or too long can inhibit the incorporation of the polymeric acceptor into the donor columns, the... 

Photoconductive properties are observed for some discotic molecules having abundant it electrons [16-20]. For example, triphenylene derivatives can show high charge carrier mobility in the hexagonal columnar (Colh) LC phase due to their ordered molecular packing [16-20,43-45]. 

TNF-CT complexes of 2,3,6,7,10,11-hexakispentyloxytriphenylene or related amphiphilic derivatives are also able to form Langmuir-Blodgett (LB) films [57]. Polarized UV/VIS and infrared spectra of those of TNF complexes of hexakisalkyloxytri-phenylenes discussed here, for example, indicate a preferred orientation of the columnar axes parallel to the surface and to the dipping direction [57 a]. An amphiphilic triphenylene derivative with a pair of co-OH chains and four pentyloxy groups, forming a lamellar mesophase in the neat state, a nematic discotic main chain polymer derived from the aforementioned monomer both exhibit induced columnar hexagonal (Col j,) mesophases with TNF in the bulk state [57b]. The X-ray diffraction pattern of the... 

US with a great benefit for device applications requiring large-areas. For the discotic columnar phases, there are few reports of the effect of structural defects on charge carrier transport. Unlike the smectic mesophases, where two dimensional transport takes place, it is likely that structural defects in a column may affect the carrier transport properties seriously, because a carrier has to pass along a column without detouring to adjacent columns. From this point of view, relatively low mobility in the columnar ordered phase of triphenylene derivatives, where the intermolecular distance is as small as 3.5 A, may be explained by the structural defects or disorder of molecular alignment in the columns as described above. 

Wegewijs, B.R., et al. Charge-carrier mobilities in binary mixtures of discotic triphenylene derivatives as a function of temperature. Phys. Rev. B Condens. Matter Mater. Phys. 65(24), 245112/1-245112/8 (2002). doi 10.1103/PhysRevB.65.245112... 

Akopova reported liquid crystalline phthalocyanines 116ac (Scheme 63) with eight peripheral crown ethers devoid of alkyl chains [132]. Nonetheless, discotic nematic phases could be observed as derived from miscibility experiments with the discotic nematogen hexa(cyclohexanebenzoyloxy)triphenylene and optical textures. In the case of metal-free 116a, a phase width of 43 K was found. Complexation with Zn(II) (116b) decreased the phase range to 35 K and with... 

---