DOI: https://doi.org/10.55373/mjchem.v27i5.95

Keywords: Liquid crystals; amide; nematic; alkyl chains; mesophase

Abstract

A series of new hybrid amide-based liquid crystals was successfully synthesized and characterized. The 4-alkoxybenzoic acids (1a–b) were synthesized via the alkylation and subsequent saponification of methyl 4-hydroxybenzoate using heptyl and decyl bromide, respectively. The amidation of compounds 1a–b with thionyl chloride and 1,4-phenylenediamine yielded N,N'-(1,4-phenylene)bis(4-substituted benzamides) (2a–b), which possess a symmetrical structure. These compounds were characterized using Fourier transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, and CHN elemental analysis. The determination and conformation of liquid crystal properties were achieved using polarized optical microscope (POM) and differential scanning calorimetry (DSC). The main functional groups in compounds 2a–b can be seen in the FT-IR spectrum by the characteristic stretching vibrations of C_sp3-H, C=O, C=C, and C-O stretching at ~ 2900 and 2850, 1700, 1600, and 1290 cm^-1, respectively. In the ¹H-NMR spectrum, a singlet peak at δ 9.24 ppm showed the presence of amino groups in the compound, indicating the successful formation of amide linkage. Compounds 2a–b show nematic phase with schlieren texture at 131.4 and 130.9 ℃, respectively. The DSC thermograms of compounds 2a–b demonstrate two transitions, thus confirming the presence liquid crystals transition. The structure property relationship between the alkyl chains, symmetrical structure, and linkage units serves as the main factor influencing the presence of mesophase.