Symmetric mesogenic twins derived from salicylaldimines

The synthesis, characterization, and mesomorphic properties of a series of symmetric dimeric twins derived from mesogenic salicylaldimines 1a–e are reported. In order to understand the structure–property relations, the bridged spacer (m=5, 6, 7, 8, 9), and alkoxy chains (n=6, 8, 10, 12, 14) were systematically varied. Except for 1a, all derivatives 1b–e exhibited mesophases whose mesomorphic properties strongly depended on the spacer parity and the alkoxy chains. Dimers 1a exhibited crystal or SmX phases. Other dimers 1b–e were truly mesogenic, giving enantiotropic SmC, SmA or/and N phases. Odd–even effect was observed on phase temperatures, and nematic phases were observed for derivatives with odd spacer, and a value of d/l=0.92 (1a; m=5, n=8)–0.84 (1c; m=7, n=14) was obtained by powder X-ray diffraction data, therefore, a monolayer structure in mesophase was proposed.