Effect of a Central Group on Mesomorphism

Abstract

A novel homologous series: 4-(4′-n-alkoxy benzoyloxy)-4^″-methoxy benzyl benzoates is studied with a view to understanding the effect of a central group on the phenomenon of mesomorphism. The novel homologous series consists of eleven compounds. Mesomorphism commences from the second member of a series. All the mesogenic homologues from ethoxy to hexadecyloxy exhibit nematogenic mesomorphism without the exhibition of smectogenic character. The nematic–isotropic transition curve of the phase diagram behaves in normal manner up to the dodecyloxy homologue and then deviated for the tetradecyloxy and hexadecyloxy homologues. The solid-isotropic or nematic transition curve adopts a normal behavior in a zigzag manner. The nematic-isotropic transition curve shows an odd-even effect and continues up to the octyloxy homologue. Transition and melting temperatures including the textures of mesophases are determined by an optical polarizing microscope, equipped with a heating stage. The textures of the nematic mesophase are threaded or Schlieren in type. Analytical data and spectral data support the molecular structures. The mesomorphic behavior of the present series is compared with structurally similar other known series of differing central group (viz. ‒N˭N‒ and ‒CO‒CH˭CH‒) keeping rest of a molecular part unchanged. The nematic thermal stability of the series is 236.8°C of a high melting type present series whose nematogenic mesophase length varies between 27°C and 98°C. Thus, series is only nematogenic without exhibition of a smectic mesophase.

Keywords:

• Central bridge
• mesogen
• mesomorphism
• nematic
• smectic

Acknowledgments

Authors acknowledge thanks to the Green Circle Inc. Lab for research facilities services as and when needed. Authors also thank Dr. Vipul Patel and Dr. M. L. Chauhan for their valuable helping hand and microscopic facility. Thanks are due to the Sophisticated Analytical Instrumentation Facility, Punjab University, Chandigarh for analytical services.