Liquid crystalline compounds having a tribranched structure: substituted malonic esters consisting of two Schiff's base units and a cholesteryloxyalkyl substituent

New tribranched thermotropic liquid crystal compounds were synthesized and their liquid crystalline properties studied by differential scanning calori metry, X-ray diffraction and polarizing optical microscopy. The compounds a re the bis-{10-[4-(4-alkylphenyliminomethynyl)phenoxy]decyl} 2-[6-(choleste ryloxy)hexyl]malonates and the corresponding alkoxy derivatives. These comp ounds contain three mesogenic units, two identical Schiffs base type mesoge ns and one cholesteryl either moiety, interconnected in a tribranched struc ture via spacers. The cholesterly moiety is attached to the malonic acid co re through an oxyhexamethylene spacer while the two Schiff's-base moieties are attached through oxydecamethylene spacers. The terminal alkyl group of the Schiff's base unit is either a butyl or decyl group, and the alkoxy ter minal group is either a butoxy or decyloxy chain. All the compounds form on ly an enantiotropic smectic phase, most probably of the smectic C type. The larger spacings determined by small angle X-ray diffraction range from 3.3 to 4.1 nm, which are much shot-ter than the end-to-end distance (5.9-7.4 n m) of the molecules estimated using molecular models assuming an all trans extended conformation for all the alkyl spacers.