SYNTHESIS, TRANSITION-TEMPERATURES, SOME PHYSICAL-PROPERTIES AND THE INFLUENCE OF LINKAGES, OUTBOARD DIPOLES AND DOUBLE-BONDS ON SMECTIC-C FORMATION IN CYCLOHEXYLPHENYLPYRIMIDINES

A trans-1,4-disubstituted cyclohexane ring has been introduced into kn own two-ring phenylpyrimidines to produce a wide variety of new three- ring cyclohexylphenylpyrimidines. The length and type of the terminal chains and linking units have been varied systematically. The effect o f introducing a carbon-carbon double bond of defined configuration int o various positions of both terminal chains has also been investigated . The influence of lateral dipoles (i.e. oxygen and carboxyl groups) i n different positions (central and terminal) in the molecular core of a model system on the smectic C (S(c)) transition temperature has been studied and related in a simple empirical way to standard theories fo r S(c) phase formation. Isolated, non-conjugated outboard dipoles (i.e . in cyclohexyl ethers and esters) have been found to destabilise the S(c) and nematic (N) phases. Conjugated outboard dipoles (i.e. in phen yl ethers and esters) lead to substantial increases in the S(c) transi tion temperature and usually to a widening of the S(c) temperature ran ge. Most of the new cyclohexylphenylpyrimidines exhibit a variety of s mectic phases as well as S(c) and N phases. Several homologous series of the most interesting cyclohexylphenylpyrimidines incorporating oxyg en atoms or carboxy groups and/or a carbon-carbon double bond were syn thesized and found to exhibit a relatively wide-range S(c) phase at el evated temperatures. In admixture with a chiral smectic C (S(c) base mixture, some of the new three-ring cyclohexylphenylpyrimidines can in duce a substantial increase in the S(c) and N transition temperatures without increasing the viscosity (and thus response times) excessivel y.