Andrew N. Cammidge

Structural factors controlling the transition between columnar-hexagonal and helical mesophase in triphenylene liquid crystals

A series of novel triphenylenes has been synthesised by a combination of palladium catalysed coupling, oxidative cyclisation, bromination and nucleophilic aromatic substitution. The new derivatives are designed to have structures which are intermediate between the known symmetrical materials hexakis(hexyloxy)triphenylene and hexakis(hexylthio)triphenylene. The compounds having four hexyloxy and two hexylthio substituents form only Colh mesophases. Triphenylenes having four hexylthio and two hexyloxy substituents also give Colh mesophases but 3,6-bis(hexyloxy)-2,7,10,11-tetrakis(hexylthio)triphenylene 5 is unique in that it cools into a stable, more ordered phase. The low temperature phase, which appears to be indefinitely stable at ambient temperature, is assumed to be helical based on transition enthalpy data.

A Mesogenic Triphenylene−Perylene−Triphenylene Triad

A straightforward synthesis of triphenylene-perylene-triphenylene triad structures has been achieved by using versatile triphenylene intermediates bearing a single oxyalkyl amine side chain. Among these, PBITP(10) showed a stable columnar mesophase implying favorably matched core-core separations in the structure. Importantly, the triad can be used as a vehicle for doping columnar triphenylene matrices with functional but incompatible perylene units and a mixture of hexahexyloxytriphenylene matrix doped with 0.1% PBITP(10) is homogeneous and liquid crystalline.

α-Halogenation of triphenylene-based discotic liquid crystals : towards a chiral nucleus

In an attempt to prepare chiral discotic liquid crystals based on a helically twisted triphenylene nucleus a route has been developed for the introduction of α-fluoro, -chloro and -bromo substituents and it is shown that multiple α-halogenation is also possible. The monosubstituted derivatives all show enhanced mesophase stability whilst formation of the mesophase is suppressed for the polyhalogenated derivatives. Rather surprisingly, reaction of 2,3,6,7,10,11-hexahexyloxytriphenylene (HAT6) with iodine monochloride results in chlorination rather than iodination.

The creation of long-lasting glassy columnar discotic liquid crystals using ‘dimeric’ discogens

‘Dimeric’ discogens have been synthesised which have two triphenylene nuclei, each of which bears five β-OC 6 H 13 substituents, which are linked through the remaining β positions by a flexible O(CH 2 ) n O polymethylene chain (n=3-16). Calculations show that the minimum chain length for bridging between columns in the Col h phase of these compounds is O(CH 2 ) 7 O. It was found that only those dimers for which n>7 formed a Col h phase. This mesophase can be supercooled into a metastable glass which is relatively hard and in which the columnar order and orientation is retained. These glasses revert to the crystalline state within a few hours but we have shown that longer-lasting Col h glasses can be engineered through introducing an extra degree of disorder into the glass by making the ‘dimers’ subtly unsymmetrical. These ‘dimers’ either have differently substituted triphenylene rings at the two ends of the linking chain or an amide group within the chain itself. They give Col h aligned glasses which last for months at room temperature.

Synthesis of crown ether-linked discotic triphenylenes.

Novel triphenylene dimers linked by a central crown ether core have been synthesized and characterized. The crown ether is most conveniently formed as a final step to permit purification and isolation of ion-free material, and extension of the protocol permits synthesis of triad structures linked though a 27-crown-9 macrocycle. The latter compounds present a new discotic motif that supports mesophase formation.

The effect of size and shape variation in discotic liquid crystals based on triphenylene cores

The triphenylene core provides a versatile platform from which discotic liquid crystals can be constructed. Synthetic advances permit the effect that substantial or subtle variation on structure has on mesophase formation. Through comparison of many derivatives, from our studies and others, it appears that the discotic core should be viewed as the triphenylene unit plus the attached polarizable substituents. Disruption of these extended cores discourages mesophase formation.

Phthalocyanine Analogues: Unexpectedly Facile Access to Non‐Peripherally Substituted Octaalkyl Tetrabenzotriazaporphyrins, Tetrabenzodiazaporphyrins, Tetrabenzomonoazaporphyrins and Tetrabenzoporphyrins

Controlled syntheses of phthalocyanine/benzoporphyrin hybrid structures have been achieved. We report a simple means for obtaining non-peripherally octaalkyl-substituted derivatives of tetrabenzotriazaporphyrin (TBTAP), tetrabenzodiazaporphyrin (TBDAP), tetrabenzomonoazaporphyrin (TBMAP) and tetrabenzoporphyrin (TBP) macrocycles by treating 3,6-dialkyl phthalonitriles with differing amounts of the Grignard reagent MeMgBr. This range of macrocyclic products is not obtained from corresponding reactions of a Grignard reagent with 4-substituted phthalonitriles, reported previously, or reaction of MeMgBr with a 4,5-dialkyl phthalonitrile. Attempts to form a meso-substituted TBTAP from 3,6-dialkyl phthalonitriles by reaction with benzyl and long-chain alkyl Grignard reagents unexpectedly gave only the parent macrocycle unsubstituted at the meso position. The synthetic protocols are by far the most straightforward and convenient means to access these interesting, but scarcely studied, classes of material. The new series of substituted macrocyclic compounds, obtained as the metal-free and magnesium- and copper(II)-metallated derivatives, show trends in the UV/Vis spectra consistent with those predicted elsewhere by Kobayashi. Characterisation of the new families allows further trends to be identified as meso-nitrogen atoms are sequentially replaced by methine bridges, for example, the compounds provide novel examples of macrocyclic structures that show columnar mesophase behaviour. Single-crystal X-ray structure determinations have been obtained for three magnesium-metallated derivatives bearing eight hexyl substituents and constitute the first set of structural data obtained for such a series.

Cyano substituted triphenylene-based discotic mesogens

Cyano groups have been introduced into alkoxytriphenylene-based mesogens by bromination followed by treatment with copper(I) cyanide. The introduction of cyano substitutents enhances the mesophases ranges.

The first asymmetric Suzuki cross-coupling reaction

The first asymmetric coupling reactions between aryl halides and aryl boronates (Suzuki coupling) are described to give binaphthalene derivatives in up to 85% ee.

Functionalisation of Triphenylene Based Discotic Liquid Crystals

Abstract Nitration of hexahexyloxytriphenylene results in a dramatic enhancement of the mesophase range and offers wide potential for the further functionalisation of triphenylene discotics for device applications.