Synthesis, Mesophases, and Combined Thermal, Structural, and Spectroscopic Analysis of Photoresponsive Azobenzene Alkanoates (10OABOOCm).

A homologous series of (E)-4-[(4-decyloxyphenyl)diazenyl]phenyl alkanoates (10OABOOCm, m = 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 (m = 1-11), smectic A for two derivatives (m = 1 and 2), smectic C for most compounds (m = 2-19), additional hexatic smectic phases in narrower ranges (SmF: m = 6-13; SmI: m = 9-19), and crystal-like G phase (m = 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 k = 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.