Novel heptasubstituted triphenylene discotic liquid crystals

The synthesis and characterisation of several hepta-substituted triphenylene derivatives are reported. These unsymmetrically substituted triphenylene derivatives are of three varieties, i) with seven identical peripheral alkoxy chains, ii) two or three out of the seven alkoxy chains have different chain lengths and, iii) the mode of the attachment of two of the peripheral chains is different, i.e. via ester linkages. The heptaalkoxytriphenylenes were prepared by two different routes, either starting from monohydroxypentakis(alkoxy)triphenylenes or via a biphenyl route using either MoCl5 or FeCl3 as oxidants. Unsymmetrical substitution has a large effect on the thermal behaviour but the type of mesophase formed does not change. Photomicroscopic pictures of all the 21 liquid crystalline compounds reported here show classical textures of an ordered hexagonal columnar (Col(h)) phase. X-Ray diffraction studies of five representative compounds confirmed the above conclusions. Mixed ether-ester derivatives have smaller core-core separations and higher correlation length, therefore, are better candidates for charge transport studies.