Synthesis, Structural and Mesophase Characterization of Three Ring Based Thiophene Liquid Crystals

Abstract

Thiophene based calamitic mesogens are receiving paramount importance due to their applications in functional organic materials. The insertion of thiophene in the core unit favours a large change in mesophase characteristics as well as application properties in contrast to those mesogens with phenyl ring core alone. In this work, we report the structural as well as mesophase characterization of six mesogens which are built with a core of three phenyl rings and thiophene ring. The thiophene ring is placed at one end of the core and varied the other end with alkyl/alkoxy chains to investigate the mesophase characteristics. The molecular structures of representative mesogens are confirmed by means of FT-IR and Two-dimensional solution NMR techniques. An enantiotropic nematic phase is observed in all the cases as supported by HOPM and DSC techniques. The mesophase characteristics such as melting and clearing temperatures and phase stability are discussed. A dramatic increase in nematic phase stability for the synthesised mesogens is noticed in contrast to two phenyl ring based thiophene mesogens reported in literature.

Keywords:

• Mesogens
• Thiophene
• Calamitic
• Nematic
• NMR
• Chemical Shifts

Acknowledgments

MKR and TNS are thankful to Dr. A. B. Mandal, Director, CSIR-CLRI for his keen interest and encouragement for our work. MKR expresses thanks to Mr. D. Muralidharan, Ms. N. Priya and Mr. L. Edwin Paul, CLRI for their help in recording DSC and TGA measurements. The partial financial support from NWP-23 project is duly acknowledged.