Complex formation in mixtures of 4,4'-disubstituted diphenyldiacetylenes with cyanobiphenyls

Abstract

We investigated 1:1 mixtures of a variety of 4,4'-disubstituted diphenyldiacetylenes (PTTP series) and cyano-containing mesogens for possible complex formation. Complexes were formed when alkyl/alkoxy cyanobiphenyls (CB series) were mixed with alkyl/alkoxy PTTP homologues. We found complexes having a melting temperature higher than that for either component, and complexes with lower melting temperatures. A fluoro substituent on the PTTP gave an enhanced nematic phase and a cyclohexane ring in place of a benzene ring yielded an enhanced smectic A phase, but a cyano on the PTTP gave poor liquid crystalline properties. Phase diagrams were constructed for PTTP-24/5-CB and PTTP-24/80-CB mixtures. Both complexes formed had melting temperatures higher than those for either component. These complexes were recrystallized and shown by X-ray studies to be 1:1 complexes. The PTTP-24/5-CB complex showed only a monotropic nematic phase, but the PTTP-24/80-CB complex showed induced smectic A and hexatic B phases in addition to an enantiotropic nematic phase.