Dependence of mesomorphism on geometrical shapes of isomeric and nonisomeric series of chalconyl esters

ABSTRACT

A meta substituted chalconyl ester homologous series: RO‒C₆H₄‒COO‒C₆H₄(meta)‒CO‒CH˭CH‒C₆H₄‒OC₁₂H_25(n)(para) is synthesized and studied with a view to understanding the effect of molecular substitution at meta position in a molecular structure on thermotropic liquid crystal properties. The novel homologous series consists of thirteen homologues (C₁ to C₁₈). All the homologues except the nonliquid crystal homologues C₁, C₂, C₃ are enantiotropic nematic with the absence of smectic properties. The transition and melting temperatures were determined by an optical polarizing microscopy (POM) equipped with a heating stage. Textures of a nematic phase are threaded or Schlieren. Transition curves (Cr-N/I and N-I) behave in normal manner except homologues between C₁₀ and C₁₄ of N-I curve, which show negligible deviation from normal and a smooth descending tendency. The N-I transition curve exhibits an odd-even effect up to C₁₀ homologue and then the odd-even effect disappears for higher homologues. Analytical and the spectral data support the molecular structures. Thermal stability for nematic is 107.3°C and the mesophase lengths range between 13.0°C and 35.0°C at the C₁₈ and C₁₂ homologues respectively. Group efficiency order for nematic is derived on the basis of thermal stability as ‒OC₁₂H_25(n) (linear) > ‒OC₁₂H_25(n) (nonlinear) > ‒OC₁₆H₃₃ (nonlinear).

KEYWORDS:

• Mesomorphism
• liquid crystal
• nematic
• smectic
• enantiotropic

Acknowledgments

The authors thank the management of the college and the Head of the Chemistry Department Dr. R. B. Patel of K. K. Shah Jarodwala Maninagar Science College, Ahmedabad for their valuable cooperation in the work. The authors are also thankful to Dr. A. V. Doshi, Ex-Principal, M. V. M. Science and Homescience College, Rajkot for his co-operation, valuable suggestions and help as and when needed during the course of present investigation. Thanks are due to NFDD Centre, Saurashtra University, Rajkot for analytical and spectral services.