New mesogenic materials bearing 1,2,4-oxadiazole moiety: Synthesis, characterization and investigation their mesomorphic behaviors

ABSTRACT

In this work, two series containing a 1,2,4-oxadiazole ring as a central core were synthesized and characterized by common spectroscopic techniques, including FT-IR, ¹H-NMR, and elemental analysis. The first series was 3-(4-alkoxyphenyl)-5-(p-methylphenyl)-1,2,4-oxadiazole (C_n), which consisted of alkoxy group in the terminal arm and a methyl group in the other, while, the oxidation reaction of methyl group in a series (C_n) to the carboxy group was the method used to synthesize the second series in this work, 4-(3-(4-alkoxyphenyl)-1,2,4-oxadiazol-5-yl)benzoic acid (D_n). The mesophase behaviors of these two series were studied by optical polarized microscopy (OPM) and differential scanning calorimetry (DSC). The liquid crystalline investigations of the compounds (C_n and D_n) show that the last six homologeus of the series (C_n), (C₆–C₁₁), have a monotropic nematic phase, while only the intermediate compounds in the series (D_n), (D₃–D₉), displayed monotropic nematic phase, also, the liquid crystalline properties in the first and last two compounds in this series (D₁, D₂, D₁₀, and D₁₁) had disappeared. The differences in liquid crystalline properties between the two series, (C_n and D_n), were discussed through the influences of the different terminal groups (–CH₃ and –COOH) in addition to the effect of the 1,2,4-oxadiazole ring and the length of the terminal alkyl chain.

KEYWORDS:

• Oxadiazole
• dimer hydrogen bonding
• mesomorphic properties

Acknowledgments

We would appreciate all the staff of the chemistry department in Al-Mustansiriyah university for those collaborations with us in the fruition of the prerequisites about this study. Also, we would like to thankful Dr. Dhafir Al-Heetimi (Baghdad University) and Dr. Mohanad Masad (Al al-Bayt University, Jordan) for supporting us the ¹H-NMR and DSC analyses, respectively. Additionally, much appreciate to ASTF (Arab Science and Technology Foundation) due to supplying our laboratory with OPM connected to hot-stage part.