Crystalline - Smectic C - Cubic - Isotropic - Nematic - Isotropic Polymorphism: Synthesis and Unexpected Behaviour of a New Series of Double-Swallow-Tailed Mesogens

A new homologous series of six-ring double-swallow-tailed mesogens was prepared and investigated. Liquid-crystalline properties strongly depend on the length of the terminal alkyl chains. Six different phase sequences could be detected, two of them were unknown up to now. The derivatives DS-5 …7 show smectic C, cubic and nematic phases, the longer-chain homologues DS-10 … 14,16 have columnar phases. The substance DS-8 exhibits the most interesting phase sequence cr - SC- cub - Ire - N - I. DS-8 represents the second pure compound with a stable reentrant isotropic phase. Optical, X-ray, and further investigations provide arguments to propose the structures of the different phases.