LIQUID-CRYSTAL TRANSITION-TEMPERATURES AND PHYSICAL-PROPERTIES OF SOME NEW ALKENYL-SUBSTITUTED PHENYLPYRIMIDINE AND PHENYLPYRIDINE ESTERS

We have introduced a carbon-carbon double bond into the 4-(5-n-alkylpy rimidin-2-yl)phenyl alkanoates and the 4-(5-n-alkyl-2-pyridyl)phenyl a lkanoates to produce the corresponding alkenoates. The position and na ture (E/Z) of the double bond have been varied systematically and the effect on the liquid-crystal transition temperatures has been studied. The new alkenoates exhibit nematic and (primarily highly ordered) sme ctic phases. A smectic C phase is only observed for a limited number o f homologues. The alkenoates with a trans double bond in the 2-positio n possess broad nematic phases at elevated temperatures as well as a v ariety of smectic phases at lower temperatures. In admixture with a ch iral smectic C base mixture, some of the (E)-alk-2-enoates can induce a substantial increase in the chiral smectic C and nematic transition temperatures. The temperature of crystallisation is not affected adver sely. Thus, the temperature range of the chiral smectic C mesophase ca n be significantly increased. The (E)alk-2-enoates can also be used to induce a chiral nematic phase in chiral smectic C mixtures (which do not possess one), while at the same time increasing the temperature ra nge of the chiral smectic C phase. The novel pyrimidine and pyridine a lkenoates are of especial interest for chiral smectic C mixtures for s urface-stabilised ferroelectric display devices (SSFLCDs), where a nem atic mesophase is usually essential for good orientation.