Mesomorphism dependence on halogenated chalconyl esters in terms of molecular flexibility/rigidity

ABSTRACT

Vinyl carboxy central group containing a novel chalconyl ester homologous series: RO.C₆H₄.CH ˭ CH.COO.C₆H₄.CH ˭ CH.CO.C₆H₄.I (para) have been synthesized and studied with a view to understand and establish the relation between thermotropic liquid crystalline (LC) behaviors and the molecular structure. Novel chalconyl ester homologous series consists of thirteen homologs (C₁–C₁₈). C₁–C₃ homologs are nonmesogenic, C₄ homolog is enantiotropic nematogenic and the rest of the homologs (C₅–C₁₈) are enantiotropically smectogenic plus nematogenic. Phase transition temperatures and textures of LC phase were determined by an optical polarizing microscopy (POM) equipped with a heating stage. Cr-M/I, Sm-N, N-I transition curves in a phase diagram behaved in normal manner. Sm-N and N-I transition curves exhibited odd-even effect from C₄–C₁₀ or nearby C₁₀ homolog. Textures of nematic phase are threaded or Schlieren and that of the smectic phase are of the type smectic A or C. Analytical and spectral data confirms the molecular structure of homologs. Thermal stabilities for smectic and nematic mesophases are 155.0 and 180.7, respectively, and their corresponding mesophaselengths are varied from minimum to maximum at 17.0°C–39.0°C as well as 15.0°C–30.0°C. Thus, it is middle ordered melting type series. The group efficiency orders derived on the basis of smectic and nematic thermal stabilities are as under: Sm: -C₆H₄.I > -C₆H₄.Cl > -C₄H₃S and N:- C₆H₄.I > -C₆H₄.Cl > -C₄H₃S from comparative study of structurally similar analogous series

KEYWORDS:

• Enantiotropy
• liquid crystals
• mesophaselength
• nematic
• smectic

Acknowledgments

Authors acknowledge thanks to Dr. R.R.Shah, principal and management of K. K. Shah Jarodwala Maninagar Science College, Ahmedabad. Authors are also thankful to Dr. A.V.Doshi, Ex-principal of M.V.M. Science and Home Sci. College – Rajkot for his constant support, inspirations, and help, as well as valuable suggestions as and when we needed during the course of present investigation. Authors thank to NFDD Centre for the analytical and spectral services.