Molecular structural flexibility dependence of mesomorphism through ortho-substituted bromo group

Abstract

ABSTRACTA novel series of liquid crystal (LC) materials of Schiff's bases viz. RO-C6H4‒CH˭CH‒COO‒C6H4‒N˭CH‒C6H4‒Br (ortho) is synthesized and studied with a views to understanding and establishing the effect of molecular structure on liquid crystal properties and to provide novel thermotropic LC material to the scientific and technological community of research interest. The novel series consists of thirteen members (C1 to C8, C10, C12, C14, C16 & C18). All the members of a series are enantiotropic liquid crystals. Smectic (C10‒C18) and nematic (C1‒C18) property commence from C10 and C1 homologue respectively. Transition temperatures and the textures of homologues were determined using a polarizing optical microscope (POM) equipped with a heating stage. Transition curves Cr-M, Sm-N and N-I of a phase diagram behaved in normal manner. Odd–even effect is absent for Sm-N transition curve, but it is present for N-I curve. Sm-N transition curve is extrapolated to C8 and C6 nonsmectogenic homologues to determine and predict their latent ability for exhibition of smectic property. Analytical and spectral data confirms the molecular structures of homologues. Thermal stabilities of smectic and nematic are 85.4°C and 130.1°C °C whose upper and lower total mesophase length vary from 58.0°C to 06.0°C at the C10 and C1 = C5 = C6 homologue, respectively. Textures of nematic phase are threaded or Schlieren and smectic phase are of type A or C. LC properties of present novel series are compared with structurally series known series. Thus, present novel series is predominantly nematogenic and partly smectogenic with middle ordered melting type and considerable total mesophase length range.