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
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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.