Three-ring phenyl/biphenylpyrimidine esters: dependence of liquid-crystal transition temperatures and other physical properties on the position of the nitrogen atoms and the double-bond configuration

Abstract

We have introduced a carbon–carbon double bond into four series of three-ring phenyl/biphenylpyrimidinyl octanoates to produce the corresponding octenoates. The position of the two nitrogen atoms in each series is different. For each of the four separate isomeric series the position and nature (E/Z) of the double bond have been varied systematically and the effect on the liquid-crystal transition temperatures studied. The new octenoates exhibit nematic (N) and (sometimes highly ordered) smectic phases. A smectic C (S_c) phase is observed for most isomers. Four homologous series of alkenoates with a trans double bond in the 2-position [(E)-2] were prepared. Three series of the (E)-alk-2-enoates possess broad S_c and N phases at elevated temperatures. One homologous series is purely N. In an admixture with a chiral smectic C (S_C*) base mixture, some of the (E)-alk-2-enoates can induce a substantial increase in the S_C* and N transition temperatures. The temperature of crystallization is not affected adversely. Thus, the temperature range of the S_C* mesophase can be significantly increased without increasing the viscosity (and thus response times) excessively. The (E)-alk-2-enoates can also be used to induce a chiral nematic (N*) phase in S_C* mixtures (which do not possess one), while at the same time increasing the temperature range of the S_C* phase.