Liquid-crystal transition temperatures and physical properties of some new alkenyl-substituted phenylpyrimidine and phenylpyridine esters

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Abstract
We have introduced a carbon–carbon double bond into the 4-(5-n-alkylpyrimidin-2-yl)phenyl alkanoates and the 4-(5-n-alkyl-2-pyridyl)phenyl alkanoates to produce the corresponding alkenoates. The position and nature (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) smectic phases. A smectic C phase is only observed for a limited number of homologues. The alkenoates with a trans double bond in the 2-position possess broad nematic phases at elevated temperatures as well as a variety of smectic phases at lower temperatures. In admixture with a chiral 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 adversely. Thus, the temperature range of the chiral smectic C mesophase can 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 range of the chiral smectic C phase. The novel pyrimidine and pyridine alkenoates are of especial interest for chiral smectic C mixtures for surface-stabilised ferroelectric display devices (SSFLCDs), where a nematic mesophase is usually essential for good orientation.