Green Synthesis and Mesomorphic Characteristics of a Phenoxyethyl tail with Alkoxy Benzoate Homologous Series

Abstract

A novel mesogenic homologous series of phenoxyethyl-tailed benzoates, namely 4-((3-phenoxypropanoyl) oxy) phenyl 4-n-alkoxybenzoate (Series PXn), was synthesized and systematically investigated to evaluate the influence of terminal alkoxy chain length and phenoxyethyl moiety on mesomorphic behavior. The compounds were prepared via conventional and green synthetic routes and characterized by FT-IR, and 1H NMR spectroscopy. Mesophase behavior was examined using polarizing optical microscope (POM) and differential scanning calorimetry (DSC). The lower homologues (PX1 & PX2) were found to be non-mesogenic, while intermediate members exhibited monotropic nematic or Smectic A (SmA) phases. Notably, PX3 & PX4 displayed monotropic nematic and smectic A mesophase. Higher homologues (n ≥ 5) displayed enantiotropic SmA mesophases with decreasing transition temperatures upon increasing alkyl chain length. Differential scanning calorimetry (DSC) thermograms exhibited distinct phase transition temperature, indicating a clear homologous dependence of the thermal properties. Structural comparison further revealed that the presence of the phenoxyethyl terminal group and the benzoyloxy central linkage plays a crucial role in modulating molecular polarizability and mesophase stability. Overall, this study emphasizes the structure– property relationship that governs phase transition behavior in phenoxyethyl-based liquid crystalline systems.