Symmetric and non-symmetric liquid crystal dimers with branched terminal alkyl chains: Racemic and chiral

Two new series of racemic dimeric liquid crystals containing terminal alkyl chains with methyl branches are presented; in one the dimers are symmetric and in the other they are non-symmetric. Comparisons are made with the structurally isomeric series with no methyl branches in their terminal alkyl chains. The stability and clearing temperatures of the liquid crystal phases are markedly reduced for the dimers with methyl branches, particularly for the symmetric dimers. Chiral analogues oi both series were also examined. The liquid crystal behaviour of the non-symmetric dimers is of particular interest. Four homologues were studied with the number of methylene units in the spacer ranging from six to nine. An odd-even effect was observed for the chiral properties of these materials. Blue phase I behaviour was exhibited by the heptane and nonane homologues but not by the even membered hexane and octane members of the series.