Mesomorphic Properties of Four-Ring Systems Bearing No Terminal Substituent

Abstract

Temperatures of the solid-nematic and nematic-isotropic transitions have been measured for forty-eight diverse compounds bearing no terminal substituent. Four benzene rings are connected to each other by single carbon-carbon bond(s) and/or by carbonyloxy, azomethine, and azo groups. The consequence of any linking group placed centrally in a quaterphenyl molecule is a drastic suppression of the solid state stability. The nematic-isotropic transition is hardly affected by the introduction of an azo linkage and also by an azomethine one, whereas it is significantly depressed by a carbonyloxy linkage. The presence of two or three linking groups yields generally complex effects on the thermal behavior because of the marked interdependence of the effects of the linking groups. No efficiency order in promoting a nematic phase applicable to all the compounds could be established.