Influence of Ortho-Trifluoromethyl Substitution on the Mesomorphic and Thermal Behavior of Azo-Ester Liquid Crystals: Experimental and DFT Insights

A new homologous series of azo-ester-based liquid crystals bearing an ortho-trifluoromethyl (–CF3) substituent has been synthesized and characterized to explore the influence of lateral fluorination on mesomorphic and thermal behavior. The series comprises derivatives with varying alkoxy chain lengths (C3-C8, C10, C12, and C14). Structural confirmation was achieved through FT-IR, ¹H NMR, and mass spectrometric analyses. Differential scanning calorimetry (DSC) and polarizing optical microscopy (POM) studies revealed that the first four members (C3–C6) are non-mesomorphic, while the higher homologues (C7–C14) exhibit monotropic smectic phases, indicating that the elongation of the terminal alkyl chain favors mesophase formation. Thermogravimetric analysis (TGA) demonstrated good thermal stability of the compounds. Density functional theory (DFT) calculations provided optimized geometries, HOMO–LUMO distributions, molecular electrostatic potential (MEP) maps, and dipole moments, supporting the experimental findings and elucidating the effect of the ortho –CF3 group on molecular polarity and planarity. The combined experimental and computational results highlight how ortho-trifluoromethyl substitution affects both the mesomorphic and thermal properties of azo-ester-based liquid crystals.