Unsymmetrical banana-shaped liquid crystalline compounds derived from 2,7-dihydroxynaphthalene

Abstract

The synthesis and characterization of new asymmetric bent-core compounds derived from 2,7-dihydroxynaphthalene with various connecting groups between the aromatic rings and alkyloxy terminal substituents at the end of the long arm are presented. Some 1,4-disubstituted phenylene rings with an azo or ester linkage between them have been used as calamitic pro-mesogen units. The synthetic strategies to obtain the final esteric derivatives involved the esterification of 7-(benzyloxy)naphthalen-2-ol with 4-((4-(alkyloxy)phenyl)-azo)benzoyl chlorides or with 4-((4-(alkyloxy)benzoyl)oxy)benzoic acids in the presence of dicyclohexylcarbodiimide (DCC) and 4-(dimethylamino)pyridine (DMAP). The mesomorphic properties were assigned by optical polarizing microscopy and differential scanning calorimetry. All the compounds showed mesomorphic properties of the enantiotropic or monotropic type, the liquid crystalline behavior depending on the linking group between the phenylene rings. Thermogravimetric studies evidenced that all compounds were stable in the range of the existence of mesophases.