Liquid Crystal Formation in Binary Systems. III. Effect of the Central Double Bond Linkage on the Induction of Nematic Liquid Crystals

Abstract

Abstract The effect of central double bond linkage on the induction of liquid crystals has been examined employing eight binary mixtures of potentially mesomorphic electron donors and acceptors of the type 4-X–C6H4–Z–C6H4–OC2H5-4. The central linkage Z is –N=N–, –CH=N–, or –CH=CH– group. The terminal substituent X is a dimethylamino group in the donor compounds and a nitro group in the acceptor compounds. A stable nematic liquid crystal is observable with the systems of azo-azo and azo-azomethine compounds. When the acceptor is the nitro derivative of stilbene, a 2 : 3 molecular complex is formed and no liquid crystal can be found, irrespective of whether the partner is an azo or azomethine compound. The latent induction of nematic liquid crystals in these combinations has been proved by studies on the phase diagrams of the pseudo-binary systems with a reference nematogen, azoxy-dianisole. The nematic liquid crystal-isotropic liquid transition temperatures of both the component compounds and the equimolar mixtures depend on the central double bond linkage: the order is –CH=CH–>–N=N–>–CH=N–. On the other hand, the order of –N=N– and –CH=N– groups is reversed in the extent of the induction of nematic liquid crystals.