Thermal and Optical Properties of Self-Assembly Systems: Two Pairs of Distinct Structural Isomers

Abstract

Two homologous pairs of linear and bent structural isomers are isolated and characterized. The series, which is linear in shape, is comprised of double hydrogen bonds forming between hydroquinone and alkyloxy benzoic acid (HQ+nOBA) and hydroquinone and alky benzoic acids (HQ+nBA) respectively. The other series with the bent structure formed double hydrogen bonds between resorcinol and alkyloxy benzoic acid (Rl+nOBA) and resorcinol and alky benzoic acids (Rl+nBA) respectively. Thus two linear mesogen series HQ+nOBA and HQ+nBA and two bent homologous series Rl+nOBA and Rl+nBA are formed, which are referred as structural isomers. Formation of hydrogen bond is conformed by FTIR, while the proposed structure is conformed by proton and carbon NMR studies. Transition temperatures and phases have been identified by differential scanning calorimetry and optical polarizing microscopic studies. Phase diagrams have been constructed for all the homologous series. The homologous series with oxygen atom in benzoic acid moiety is observed to exhibit rich phase variance compared to the series without oxygen atom. Comparison of transition temperatures, occurrence of phases, and other related properties are discussed.

Keywords:

• Hydrogen bonded liquid crystals
• isomers
• NMR
• phase diagrams

Acknowledgments

The authors acknowledge the financial support rendered by All India Council for Technical Education (AICTE), Department of Science and Technology (DST), and Defense Research Development Organization (DRDO), New Delhi. Infrastructural support provided by Bannari Amman Institute of Technology is gratefully acknowledged.