Synthesis and phase transition behaviours of laterally substituted liquid crystals containing methylhydroquinone: emerging of smectic C phase for higher homologues

Abstract

A series of laterally substituted low-molar-mass liquid crystals with molecular geometry were constructed with three phenyl rings bridged through ester central groups as the rigid core and a lateral methyl group as the flexible part of a molecule, with a view to understanding and establishing the effect of molecular structure on liquid crystal behaviour. Low-molar-mass mesogens known as 1,4-bis[(4-n-alkyloxybenzoyl)oxy]toluene with different number of carbon (n) at the alkyl chain have been prepared. Their molecular structures were proposed via physical measurements and spectroscopic techniques. Mesomorphic properties were studied by using differential scanning calorimetry, optical polarizing microscopy and powder X-ray diffraction techniques. The results showed that the melting points as well as the clearing temperatures decreased upon lengthening of the terminal alkyloxy chain lengths. Members with the shorter chain (n = 2-10) exhibited nematic phase. As for higher homologues, members with n = 12, 14, 16 and 18 showed polymorphism, whereby these compounds displayed both smectic and nematic properties.