Synthesis and Characterization of Supramolecular Hydrogen-Bonded Liquid Crystals Comprising of p-n-Alkyloxy Benzoic Acids with Suberic Acid and Pimelic Acid

Abstract

Two series of supramolecular hydrogen-bonded liquid crystalline complexes have been designed and synthesized. A successful attempt has been made to form hydrogen bond between Suberic acid (SA) and Pimelic acid (PA) with p-n-alkyloxy benzoic acids (nBAO) by varying the respective alkyloxy carbon number. The first homologous series comprises of Suberic acid and p-n-alkyloxy benzoic acids (SA+nBAO), while the another series is formed between Pimelic acid and p-n-alkyloxy benzoic acids (PA+nBAO), where n represents the alkyloxy carbon number which varies from 5 to 12. These two homologous series are analyzed by polarizing optical microscope, differential scanning calorimetry, Fourier transform infrared spectroscopy (FTIR), and proton NMR studies. The formation of intermolecular hydrogen bond is evinced through FTIR and 1H-NMR. An interesting feature of PA+nBAO homologues series is the inducement of tilted smectic C phase with increasing carbon chain length. In the SA+nBAO homologues series odd–even effect is observed at isotropic to nematic transition temperatures. Phase diagrams of the above complexes are constructed and compared.