Synthesis, Mesophases, and Combined Thermal, Structural, and Spectroscopic Analysis of Photoresponsive Azobenzene Alkanoates ( <b>10OABOOC</b> <i>m</i> )

A homologous series of (<i>E</i>)-4-[(4-decyloxyphenyl)diazenyl]phenyl alkanoates (<b>10OABOOC</b><b><i>m</i></b>, <i>m</i> = 1-19) was synthesized and investigated for thermal, structural, and photoresponsive properties. Phase behavior was studied by polarized optical microscopy, differential scanning calorimetry, and thermo-optical analysis. All derivatives exhibited liquid crystalline properties: nematic phase for short chains (<i>m</i> = 1-11), smectic A for two derivatives (<i>m</i> = 1 and 2), smectic C for most compounds (<i>m</i> = 2-19), additional hexatic smectic phases in narrower ranges (SmF: <i>m</i> = 6-13; SmI: <i>m</i> = 9-19), and crystal-like G phase (<i>m</i> = 2-9). X-ray diffraction and Fourier transform infrared spectroscopy confirmed layered packing and characteristic intermolecular interactions, while dielectric spectroscopy revealed relaxation processes in the crystalline phases. UV-vis absorption demonstrated efficient E-Z photoisomerization in solution, with a photostationary state reached within ∼100 s and a rate constant <i>k</i> = 2.81 × 10^-2 s^-1. These findings show that the terminal chain length influences mesophase formation, molecular organization, and photoresponsivity in this family of azobenzene-based liquid crystals.