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The development of the cyanobiphenyls for display applications was one of the most important technological advances of the 20th century. Here, we present a personal account of how advances in biphenyl science (synthesis and application) influenced the development of discotic liquid crystals. We focus on those based on triphenylene, the most widely studied discotic core. The search for nematic discotics proved to be challenging with relatively few early examples being reported. In examples of symmetrically hexasubstituted triphenylenes, a ring of peripheral aryl ester or alkynylaryl substituents provides effective steric blocking to columnar assembly – the face-to-face molecular arrangement that is observed in the majority of triphenylene discotics. The synthetic challenges associated with early triphenylene synthesis have now been largely overcome. Efficient oxidative trimerisation of dialkoxybenzenes gave direct access to materials with high purity and at scale. The intermediates can be manipulated through deprotection and elaboration, a pathway that allowed synthesis of lyotropic (Nc) systems among others. The combination of modern cross-coupling chemistry with oxidative processes has proved versatile, leading to synthesis of unsymmetrical monomeric and dimeric systems. Dimeric systems linked by rigid bridges have been identified as a separate class of materials that show strong tendency for nematic mesophase formation. [ABSTRACT FROM AUTHOR]

Isotropic phase de-wetting of discotic liquid crystals on a surface patterned with alternating ~5-10 μm wide wetting and de-wetting stripes results in the formation of long narrow droplets. On slow cooling into the columnar phase, the liquid crystal aligns such that the columns lie either across or along the stripes. However, if the stripes are wider and/or the cooling rate is too fast, defects appear. When there are many such defects, the result is complex zigzag and wavy line optical textures, which are reminiscent of the egg and dart friezes associated with classical architecture. To a first approximation, all of these patterns can be seen as joined up fragments of developable domains in which the columns either circle a defect or propagate in a straight line. They are built up from motifs that involve bend but not splay or twist deformations; deformations that leave the two-dimensional lattice of the columnar phase unchanged. As is shown, these basic circular and straight-line motifs can be combined in a variety of different ways along the stripe but, in all of these, it is found that the defects alternate from side to side. [ABSTRACT FROM AUTHOR]

A range of triphenylene and phthalocyanine-based discotic liquid crystals (DLCs) can be aligned within micrometer-scale channels formed from SU8 patterned on silicon or glass surfaces. The channels can be filled with the DLC in its isotropic phase using capillary action. Alignment occurs spontaneously as the sample is slowly cooled into the Colh phase. Whilst all of these DLCs align with the columns perpendicular to the surface when they are 'sandwiched' between glass slides, in these channels, the DLC aligns with the column director parallel to the surface. It is also constrained to lie across the channels. The same alignment occurs when these DLCs are confined between SU8-topped interdigitated gold electrodes where it gives the optimum orientation for electrode-to-electrode conduction. The quality of the alignment depends on the particular liquid crystal used and on the width of the channel. For the Colr phase of octaoctylphthalocyanine there is additional epitaxial control over the orientation of the lattice such that the a/c face of the lattice is parallel to the surface. This is an important prerequisite for creating a bistable display device that switches by virtue of changing the direction of the tilt of the discs. [ABSTRACT FROM AUTHOR]

With the benefit of hindsight we can see that there is a pre-history to the field of discotic liquid crystals: theoretical and experimental papers that predate the 1977 paper in Pramana by Chandrasekhar, Sadashiva and Suresh. However, what is often forgotten is how boldly adventurous the Pramana paper was and how remote the chance seemed that anything important would be learnt from reinvestigating the esters of hexahydroxybenzene. By 1977 although there was some evidenceforthe possibility of making liquid crystals based on disc-shaped molecules, the evidenceagainstsuch a possibility was also very strong. [ABSTRACT FROM PUBLISHER]

We report our latest results on the development of functional triphenylene derivatives. Functionality can be introduced directly into the nucleus by, for example, nitration. Analysis of our recently determined single crystal x-ray structure of 1-nitro-2,3,6,7,10,11-hexaethoxytriphenylene (HAT2-NO2) suggests that the introduced dipole contributes significantly to the stability of the columnar structure. Synthesis of selectively hydroxylated alkoxytriphenylenes allows the functionalisation of one or more side-chains and we show examples of this in which the functional side-chain is: ethyleneoxy or ester or the side chain carries moieties such as: TTF, anthracene, ferrocene, fullerene or crown-ether. The final section details new findings on crown-ether terminated hexaalkoxytriphenylene derivatives, which form lyotropic lamellarphases. [ABSTRACT FROM AUTHOR]

The phase diagram for the binary mixture of 2,3,6,7,10,11-hexakis (4'-nonylphenyl) triphenylene and 2,3,6,7,10,11-hexakis(hexyloxytriphenylene) shows formation of a 1:1 compound with a higher clearing temperature and a greater mesophase range than either of the individual components. This and related CPI (Complementary Polytopic Interaction) compounds are compared to 'charge transfer compounds' formed on adding 2,4,7-trinitrofluoen-9-one (or one of its derivatives) to a 2,3,6,7,10,11-hexaalkyloxytriphenylene (or other discogen). There are significant differences between the actual phases formed but in terms of the local molecular packing and in terms of the stabilising interactions involved they are essentially the same. Both can be rationalised using the XED (extended electron distribution) model. In this it is assumed that dispersed coulombic and van der Waals interactions dominate and that other contributions are small. [ABSTRACT FROM AUTHOR]

This paper summarises our recent investigations on mechanically robust materials with columnar hexagonal order. Initially we address the problem of poor field injection of charge carriers from an electrode. We show that, by using the appropriate cell treatment along with the use of more ordered columnar phases, the DC dark conductivity can be improved by up to five orders of magnitude over that of materials exhibiting a conventional Colh phase. Charge carrier mobilities were determined by time of flight photoconduction for the columnar hexagonal plastic phase of 2,3,6,7,10,11-hexakis(propyloxy)triphenylene (HAT3, 0.015  cm2 V-1 s-1at 130°C). The mobilities and their temperature dependence are discussed with reference to the series of hexaalkoxytriphenylenes and a highly ordered CPI stabilised system. [ABSTRACT FROM AUTHOR]

The first oxidation (reduction) potentials have been measured by cyclic voltammetry for twenty-five different triphenylene based discotic liquid crystals and related systems. The measured potentials correlate reasonably well with values calculated at the PM3 level and can be understood in terms of substituent effects. There is a substantial difference between the oxidation potentials of the components in mixed CPI systems; a surprising finding in view of their high hole mobilities. For 2,3,7,8,12,13-hexakis(2-(2′-methoxyethoxy)ethoxy) tricycloquinazoline both CV and NMR show that there is aggregation in acetonitrile solutions. [ABSTRACT FROM AUTHOR]

An optical micrograph taken by R. J. Bushby and co‐workers using crossed polarizers shows a thin film of 1,4,8,11,15,18,22,25‐octaoctylphthalocyanine in its columnar rectangular liquid crystal phase at 100 °C. In such thin, open‐to‐the‐air films, the columns are aligned in‐plane but follow random sweeping lines. However, when open‐to‐the‐air films are confined within micrometer‐scale channels formed from SU8, all of the columns are aligned and point in the same direction, as shown on page 5997. [ABSTRACT FROM AUTHOR]