Dependence of Mesomorphism on Molecular Rigidity with Reference to Lateral Substitution and Central Bridge

ABSTRACT

A novel mesogenic ester homologous series is synthesized and studied with a view to understanding and establishing the effect of laterally substituted -OCH₃ on mesomorphic behavior. The series consists of twelve members. C₁ to C₄ members are nonmesogenic, C₆ to C₁₂ are smectogenic in addition to nematogenic, and C₁₄ to C₁₆ are only smectogenic. The textures of smectic and nematic phases are A or C type and threaded or Schlieren, respectively. The transition curves in a phase diagram exhibit an odd–even effect and behave in normal manner except for the C₁₄ and C₁₆ derivatives in Sm-I transitions. Thermometric data were determined by an optical polarizing microscope equipped with a heating stage. Average thermal stability for smectic and nematic are 107.7°C and 121.0°C, respectively. Smectogenic and nematogenic mesophase length ranges from 11.0 to 44.0°C and 12.0°C to 39.0°C, respectively. The mesomorphic properties of present series are compared with structurally similar other known series. Thus, present series is predominantly smectogenic and partly nematogenic of middle ordered melting type.

KEYWORDS:

• Liquid crystal
• mesogenic
• mesomorphism
• nematic
• smectic

Acknowledgments

The authors are especially thankful to management, principal and HOD (chemistry Dept.) of Shree M. & N. Virani Sc. College, Rajkot and Kamani Sc. College & Prataprai Arts College, Amreli for their valuable cooperation to facilitate present research work, and IR spectra. The authors are also thankful to the authorities of Saurashtra University for analytical services.