SYNTHESIS, TRANSITION-TEMPERATURES AND SOME PHYSICAL-PROPERTIES OF SOME LOW-MELTING SMECTIC-C MATERIALS

As part of a systematic study of the factors affecting the smectic C p hase, a dipole (ie, an oxygen atom) was introduced into the middle of one of the (non-polarisable) alkyl chains of a model phenylpyrimidine. A carbon-carbon double bond has also been introduced and the position and nature (E/Z) of the double bond was varied systematically and the resultant effect on the transition temperatures and several other phy sical properties of relevance to ferroelectric liquid crystal displays (FLCDs) studied. The new phenylpyrimidines exhibit nematic, smectic C and sometimes highly ordered smectic phases for long chain lengths. T he effect of the oxygen atom in a central position in the chain is oft en to reduce the melting point (T-m) more than all the other transitio n temperatures (eg, below room temperature). This often results in a w idening of the smectic C temperature range compared to the correspondi ng compounds without an oxygen atom in the middle of the chain. Of the alkenyl substituted compounds the ethers with a trans double bond in the 2-position [(E)-2-] exhibit the highest T-Sc values and lowest sme ctic A transition temperatures. The ethers with a double bond in a ter minal position of the alkenyloxy chain exhibit the widest smectic C me sophase ranges (up to 60 degrees C). Of the esters only the (E)-alk-2- enoates exhibit mesomorphic properties.