Apolar novel mesogenic symmetric dimers composed of five-ring bent-core monomeric units

Abstract

The synthesis and mesomorphic properties of parts of six different series of symmetric dimers composed of five-ring bent-core monomeric units have been investigated. By design, all the dimers are apolar as all the dipoles of the monomers cancel with each other. The mesomorphic properties have been investigated (1) as a function of the length of the terminal chain for a fixed spacer unit, and (2) as a function of the length of the spacer unit for a fixed terminal chain length. Interestingly, two orthogonal lamellar phases have been observed in many of these dimers which differ from one another only in the layer spacing. The chemical structure of the dimers has been determined using a combination of spectroscopic techniques and elemental analysis. The mesophases are characterised using complementary methods such as polarising optical microscopy, differential scanning calorimetry, X-ray diffraction and electro-optical measurements.

Keywords:

• bent-core compounds
• symmetric dimers
• ether linkage
• ester linkage
• orthogonal mesophase

Acknowledgements

The authors thank Mrs. K. N. Vasudha for technical support and Mr. Santosh Prasad Gupta for XRD measurements. They also thank the NMR Research Centre, Indian Institute of Science, Bangalore for recording the NMR spectra. BKS thanks the Indian National Science Academy, New Delhi, for financial support