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

We investigated 1:1 mixtures of a variety of 4,4'-disubstituted diphenyldia cetylenes (PTTP series) and cyano-containing mesogens for possible complex formation. Complexes were formed when alkyl/alkoxy cyanobiphenyls (CB serie s) 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 e nhanced nematic phase and a cyclohexane ring in place of a benzene ring yie lded 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 an d PTTP-24/8O-CB mixtures. Both complexes formed had melting temperatures hi gher than those for either component. These complexes were recrystallized a nd shown by X-ray studies to be 1:1 complexes. The PTTP-24/5-CB complex sho wed only a monotropic nematic phase, but the PTTP-24/8O-CB complex showed i nduced smectic A and hexatic B phases in addition to an enantiotropic nemat ic phase.