Chiral unsymmetrical bent-shaped dimers exhibiting cholesteric phases: synthesis, characterisation and liquid crystalline properties

Overview & Synopsis

Cholesteric and smectic mesophases in six new unsymmetrical bent-shaped dimers were reported.The homologous series contain a bent-core mesogen and cholesterol mesogenic unit connectedthrough a flexible pentamethylene spacer. The thermodynamic behaviour and liquid crystallinetextures were investigated by the combination of differential scanning calorimetry (DSC) andpolarising optical microscopy (POM). All derivatives present cholesteric (N*) and smectic (Sm)phases on wide thermal range except the compound with one fluorine atom as substituent thatexhibits only chiral nematic phase. For homologues with shorter terminal alkyl chains (hexyl,heptyl) the N* mesophase was narrower than to smectic mesophase, while for the derivativewith one fluorine atom into structure only it was observed on wide thermal range. The temperaturedependence of the helical pitch of the N* structure was studied, in correlation with the length ofthe alkyl chain and the presence of one lateral fluorine substituent. The results of the theoreticalinvestigation of cholesteryl derivatives were also reported.