Showing papers by "D. S. Shankar Rao published in 2000"

Novel heptasubstituted triphenylene discotic liquid crystals

Abstract: 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 (Colh) 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.

Ferroelectric switching in a novel bent-shaped mesogen having two non-mesogenic units linked by an alkylene spacer

Abstract: We report the synthesis, X-ray diffraction results and electro-optical switching measurements for a bent-shaped mesogen having two non-mesogenic units linked by an alkylene spacer. The novelty of the molecular structure lies in the carbonyl group of the ester linkage being directly attached to the spacer unit, unlike for banana-shaped molecules reported so far, in which it is one oxygen atom away from the spacer or the central aromatic unit. The compound shows two mesophases: the high temperature mesophase is a tilted smectic phase showing ferroelectric switching characteristics; the low temperature phase is more highly ordered with textural features similar to that of the B3 banana phase.

A Novel Calamitic Liquid Crystalline Oligomer Composed of Three Non-Identical Mesogenic Entities: Synthesis and Characterization

Abstract: The synthesis and evaluation of the mesomorphic properties of the first trimesogen consisting of three non-identical calamitic mesogenic entities have been described.

Synthesis and Mesomorphic Properties of Some Anthraquinone Derivatives: New Difunctionalised Discotic Monomers

Abstract: Some new 9,10-anthraquinone (rufigallol) derivatives have been prepared and their mesomorphic properties have been studied. The unsymmetrically substituted tetrahydropyranyloxy-ethers (THP-ethers), exhibited columnar mesomorphism at fairly low temperatures and the xray studies carried out for one of the homologues confirmed the hexagonal nature of the mesophase. The deprotected derivatives of these THP-ethers, also form columnar mesophases. All these derivatives are very good candidates for polymerisation studies.