Synthesis, Characterization and Mesomorphic Properties of Aromatic Acid Dimers

Abstract

In this study, a new series of acid dimers, N-(4′-carboxybenzylidene)-4-alkoxybenzoyloxyaniline [(4′-HOOCC₆H₄CH˭N)-4-C₆H₄OCOC₆H₄OR, where R = C_mH_{2m + 1} and m = 6, 8, 10, 12, 14, and 16], have been synthesized. The compounds have been characterized by elemental analyses and FTIR, UV-visible, ¹H, and ¹³C NMR spectra. The mesomorphic properties of these acid dimers were studied by differential scanning calorimetry and polarizing optical microscopy. The mesomorphic nature of these compounds depends on hydrogen bonding and on the alkoxy chain length. The compounds with m = 6 and 8 show a characteristic enantiotropic nematic mesophase, whereas those with m = 12 and 14 exhibit monotropic behavior. The compounds with m =10 and 16 exhibit non-mesomorphic behavior.

Keywords:

• Differential scanning calorimetry
• enantiotropic nematic mesophase
• monotropic nematic mesophase
• polarizing optical microscopy
• acid dimers

Acknowledgments

The authors thank the Head of the Department of Chemistry, Banaras Hindu University (BHU), Varanasi, India, for providing laboratory facilities. One of the authors (Ashwini Pandey) thanks the Council of Scientific and Industrial Research (CSIR, New Delhi, India) for financial support in the form of senior research fellowship at BHU. Thanks are also due to Mr. Satish Tiwari for CHN analyses, Mr. Shishir, Mr. Nagendra, and Mr. Amit for ¹H, ¹³C NMR, and IR and electronic spectroscopy.