Role of molecular structural flexibility on mesomorphism

ABSTRACT

A homologous series of novel chalconyl ester derivatives: RO.C₆H₄.COO.C₆H₄.CO.CH:CH.C₆H₄.OC₆H₁₃(n) shave been synthesized and studied for its thermotropic liquid crystal (LC) properties with a view to understanding and establishing the relation between molecular structure and LC properties. The homologous series consists of eleven members whose, mesomorphism commences from C₃ of the series and continues up to the C₁₆ homologue. The C₁ and C₂ homologues are nonliquid crystals. All the LC homologues are enantiotropically nematogenic with absence of smectogenic character. Transition temperatures were determined by an optical polarizing microscope (POM) equipped with a heating stage. Textures of a nematic phase are threaded or Schlieren. Analytical and spectral data confirms the molecular structures of homologues. Transition curve Cr-N/I behaved in normal manner. N-I transition curve exhibits an odd even effect; descended at C₁₀ homologue and then again rises at C₁₂ and descended from and beyond C₁₂ homologue. Thus it partly deviates from normal behaviour. Thermal stability for nematic is 95–89°C and nematogenic upper and lower mesophase lengths are 41.0°C and 07.0°C respectively. Group efficiency order for nematic on the basis of thermal stability is –OC₈H₁₇(n)> -OC₆H₁₃(n) > -OC₁₀H₂₁(n) and it is a low order melting type series.

KEYWORDS:

• Chalconyl ester
• mesomorphism
• nematic
• smectic
• enantiotropic

Acknowledgments

Authors acknowledge thanks to the Dr. N.N. Vyas, the head of chemistry department and the principal Dr. M.B. Patel and Prof.M.L. Chauhan 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, comments, co operation and support as and when needed throughout this present investigation. Authors acknowledge thanks to L.M. college of pharmacy, Ahmedabad for analytical and spectral series.