Study of mesomorphism and its relation to molecular structure through molecular rigidity and flexibility

ABSTRACT

Novel liquid Crystalline (LC) substances of chalconyl ester derivatives from Vinyl aromatic carboxylic acids are synthesized and studied with a view to understanding and establishing the relation between molecular structure, RO-C₆H₄-CH=CH-COO-C₆H₄-CH=CH-CO-C₆H₄-F (para) and LC properties of the thermotropic variety. Homologous series consists of eleven members (C₁ to C₁₆). C₁ and C₂ members of novel series are nonliquid crystals (NLC) and the rest of the homologues (C₃ to C₁₆) are enantiotropic nematic with absence of smectic property throughout. Transition temperatures and textures of homologues were determined by an optical polarizing microscope (POM) equipped with a heating stage. Textures of nematic phase are threaded or Schlieren. The transition temperatures of novel homologues are relatively lower than the corresponding dimeric trans n-Alkoxy Cinnamic acids from which, novel homologues are synthesized. Thermal, analytical, spectral data confirmed molecular structures of novel homologues. Cr-N/I and N-I transition curves behaved in normal manner except C₈ to C₁₄ homologues which deviated from normal descending tendency in N-I transition curve. N-I transition curve exhibited odd-even effect up to C₆ homologue and odd member's N-I transition curve occupied lower position than even member's N-I transition curve. Thermal stability for nematic is 118.2°C; with its total mesophase length ranging from 12.0 to 50.0°C. Thus, it is a middle ordered melting type series with absence of smectic property. Group efficiency order derived on the basis of thermal stability using comparative study of present novel series with structurally similar analogous series as mentioned below.

Smectic: Series-Y > Series- X = Series-1 and

Nematic: Series-X > Series- 1 > Series-Y

KEYWORDS:

• Liquid crystal
• Mesomorphism
• Molecular Flexibility
• Nematic
• Smectic

Acknowledgments

Authors acknowledge thanks to the Dr. N.N. Vyas, the head of chemistry department and the principal, Dr. M.B. Patel of the college for their supportive view and providing research facility of present investigation. Authors are also thankful to Dr. A.V. Doshi, Ex. Principal, M.V.M. Science and Home. Sc. College, Rajkot for his valuable suggestions, co-operation and support as and when needed throughout present investigation. Authors acknowledge comment thanks to L. M. Pharmacy college, Ahmedabad for analytical and spectral services.