Synthesis and mesomorphic properties of some bisegmented compounds derived from 4,4′-disubstituted biphenyl

Abstract

New unsymmetrical disubstituted biphenyls have been synthesized. Two different chains (one hydrocarbon and the other fluorinated) are linked through an acetamide bond to 4-methoxy-4′-hydroxybiphenyl. Their mesomorphic properties have been characterized by light microscopy and by differential thermal analysis showing the peculiar contribution of the hydrocarbon chain and the fluorinated tail. The enhancement of the hydrocarbon moiety from one to twelve methylene groups leads to a decrease of the clearing temperatures; furthermore the enantiotropic behaviour is changed to monotropic. The variation of the fluorinated moiety generates strong effects on the transition temperatures. These mesomorphic properties are compared to those of their monocatenar perfluorinated analogues incorporating a connector of the ester or monosubstituted amide type.