4 UNIT LINKING GROUPS .2. SOME NOVEL SMECTIC-C MATERIALS

About 40 diverse phenyl benzoate esters incorporating a trans-1-4-disubstituted cyclohexane ring joined to the central aromatic core by new four unit linking groups (C4H8, C4H6, C3H6O and C3H4O) have been synthesized. The effect of various lateral substituents (F, Cl, CN and Br) and especially two fluorine atoms in the 2,3-positions of the 4-n-alkoxybenzoate part of the esters has been investigated. Three homologous series of 5-n-alkyl-2-(4-phenyl)pyrimidines incorporating the same four unit linking groups have also been prepared. Many members of the ester and pyrimidine series exhibit enantiotropic smectic C mesophases at moderately elevated temperatures. Several esters and pyrimidines have been found to improve the surface alignment and temperature range of chiral smectic C mixtures for surface stabilized ferroelectric liquid crystal displays. The effect of the new four unit linking groups on the liquid crystal transition temperatures, rotational viscosity and spontaneous polarization of their host structures in a standard chiral C mixture has been studied and compared to that of analogous materials containing no central linkage and standard central linkages (-, C2H4, CH2O and COO). Several lactate ester derivatives incorporating the four unit linking groups have also been prepared and been found to exhibit a moderately high spontaneous polarization.