Liquid crystalline triphenylene

Enhanced photoconductive properties were reported for physical gels of a liquid-crystalline triphenylene derivative [112],... 

Liquid crystalline triphenylene hexacarboxyUc esters 15 have been recently synthesized and the columnar phase has been observed to align homeotropically on different substrate surfaces [82]. The alignment behavior has been studied by polarizing optical microscopy and X-ray diffraction techniques. POM shows a dark view whereas optical microscopy image displayed a dendritic texture typical of columnar hexagonal assembly. The hexagonal columnar phase displays... 

Donovan et al. reported a triblock polymeric discotic liquid crystalline 3 which has electrons as the major charge carriers. The material is a triblock copolymer consisting of a polymeric main chain discotic liquid crystalline triphenylene capped at either end with blocks of poly(ethylene oxide) [4], An upper limit of p, = 8.4 x... 

The most significant differences (i.e. independence) in the analytical methods are provided in the final chromatographic separation and detection step using GC/ MS and LC-FL. GC and reversed-phase LG provide significantly different separation mechanisms for PAHs and thus provide the independence required in the separation. The use of mass spectrometry (MS) for the GC detection and fluorescence spectroscopy for the LG detection provide further independence in the methods, e.g. MS can not differentiate among PAH isomers whereas fluorescence spectroscopy often can. For the GC/MS analyses the 5% phenyl methylpolysiloxane phase has been a commonly used phase for the separation of PAHs however, several important PAH isomers are not completely resolved on this phase, i.e. chrysene and triphenylene, benzo[b]fluoranthene and benzofjjfluoranthene, and diben-z[o,h]anthracene and dibenz[a,c]anthracene. To achieve separation of these isomers, GC/MS analyses were also performed using two other phases with different selectivity, a 50% phenyl methylpolysiloxane phase and a smectic liquid crystalline phase. 

It has been shown frequently that without the presence of strong intermolecular interactions, discotic molecules are highly mobile in the liquid crystalline state.1 They undergo both lateral as well as rotational translations, resulting in the absence of positional order. Similarly, such discotics also freely rotate in the columnar aggregates they form in solution. This lack of positional order in the columns accounts for the absence of chiral or helical supramolecular order. We will demonstrate this characteristic using results obtained for triphenylenes. 

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... 

In the case of triphenylenes, two exceptional examples of altered order in the liquid crystalline state are reported for alkoxy-substituted monomeric species with shorter alkyl chains 20 (R = — O-butyl) and dimeric molecules 90249 252 linked by flexible al-... 

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... 

Fig. 8.52 The molecular structure of the triphenylene sulphur derivative HHTT and a sketch of its liquid-crystalline columnar H phase. The H phase exhibits long-range intracolumnar correlations and thus also a lateral correlation between the columns. Column 0 is shifted relative to columns 1 and 2 by p/2 and has the opposite helicity compared to columns 1 and 2.

Perhaps one of the most important applications of chiral induction is in the area of liquid crystals. Upon addition of a wide range of appropriate chiral compounds, the achiral nematic, smectic C, and discotic phases are converted into the chiral cholesteric (or twisted nematic), the ferroelectric smectic C and the chiral discotic phases. As a first example, we take the induction of chirality in the columns of aromatic chromophores present in some liquid-crystalline polymers. " The polymers, achiral polyesters incorporating triphenylene moieties, display discotic mesophases, which upon doping with chiral electron acceptors based on tetranitro-9-fluorene, form chiral discotic phases in which the chirality is determined by the dopant. These conclusions were reached on the basis of CD spectra in which strong Cotton effects were observed. Interestingly, the chiral dopants were unable to dramatically influence the chiral winding of triphenylene polymers that already incorporated ste-reogenic centers. 

Discotic liquid crystalline molecules are diskshaped molecules [5]. Examples are hexaalkanoyloxy benzenes, hexaalkoxy triphenylenes, bis-(4-n-decyl-benzoyl)methanato copper(II), hexa-n-alkanoates of truxene, and octa-substituted phthalocyanines [6]. 

Ringsdorf and coworkers [71] have shown that it is possible to induce liquid crystalline phases, namely discotic-columnar mesophases, by doping amorphous polymers containing disk-shaped electron donors, in either the side chain or the main chain, with a low molar mass electron acceptor, as shown in Figure 3.31. The resulting complexes can be considered as diskcomb PLCs and disk PLCs, respectively [5]. The electron-rich moiety is a triphenylene unit and the electron acceptors are fluorenone derivatives. When 20-25 mol% of 2,4, 7-trinitrofluorenone (TNF) is added to the side chain polymethacrylate or polyacrylate... 

Polymerizable hexabenzoates of triphenylene 3, 4, and 5 (Scheme 3.3) are the revolutionary materials, which have made the less abundant discotic nematic liquid crystalline materials more ubiquitous in a world with LCDs more than people by acting as the compensation films for widening the viewing angle [28]. Among the polymerizable compounds, the acryloyl derivative 3 is compatible for photopolymerization speed and thermal stability. 

Till now only few examples of discotic liquid crystalline polymers are known. In the first example described in literature (1),hexasubstituted triphenylene cores as discotic sidegroups, are linked to a polysiloxane backbone via a flexible alkyl spacer. Discotic main chain polymers (2,3) posses as disclike core benzene or tripenylene derivatives with the same high degree of substitution, i.e. six. 

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