Study of mesomorphism dependence on molecular flexibility of an azoester series containing a napthyl unit

ABSTRACT

A novel azoester homologous series of liquid crystalline (LC) compounds: RO‒C₆H₄-COO‒C₁₀H₆-N:N-C₆H₄‒OC₄H₉(n) without lateral substitution has been synthesized and studied with a view to understanding and establishing the effects of molecular structure on thermotropic LC substances with reference to tailed-end group. The novel homologous series consists of 13 homologs (C₁ to C₁₈) whose nematogenic and smectogenic mesomorphism commences enantiotropically from C₆ and C₁₂ members of the series, respectively. The C₁₂–C₁₈ homologs are smectogenic and C₆–C₁₈ are nematogenic, of which C₁₂–C₁₈ homologs are smectogenic plus nematogenic. The C₁–C₅ homologs are nonmesogenic. Transition temperatures and the textures of the homologs were determined and identified by an optical polarizing microscope (POM) equipped with a heating stage. Textures of a nematic phase are threaded or Schlieren and that of the smectic phase are of the type A or C. Transition curves Cr-M/I, Sm-N and N-I of a phase diagram behaved in normal manner except N-I transition temperature of C₁₀ homolog which deviated by 9°C–10°C from normal behavior. N-I transition curve exhibited odd-even effect. Analytical, spectral, and thermal data confirms the molecular structures of homologs. Thermal stability for smectic and nematic are 115.5°C and 138.5°C, respectively whose corresponding mesophaselengths are varied from 10.0°C to 16.0°C and 13.0°C to 24.0°C, respectively. Group efficiency order for smectic and nematic are derived from comparative study of structurally similar analogous series; as smectic: ‒OC₄H₉ (n) > ‒CH₃ > ‒H; Nematic: ‒H > ‒OC₄H₉ (n) > ‒CH₃

KEYWORDS:

• Azoester
• liquid crystal
• LTT
• 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 and valuable comments and suggestions as and when needed during the course of present investigation. Authors also thank to NFDD Centre for the spectral services.