Synthesis, mesophase behaviour, and DFT analysis of ( E )-4-((4-bromo-2-methylphenyl)diazenyl)phenyl 4-alkoxybenzoates: Influence of alkoxy chain length on liquid crystalline properties

A series of (E)-4-((4-bromo-2-methylphenyl)diazenyl)phenyl 4-alkoxybenzoates were synthesized via alkylation, diazotization, and esterification. Their mesomorphic properties were studied using polarized optical microscopy with a heating stage. Short-chain derivatives showed only nematic phases, while longer chains exhibited both nematic and smectic phases with decreasing transition temperatures. DFT calculations at the B3LYP/6-31G(d,p) level provided optimized geometries, frontier molecular orbital energies, dipole moments, and MEP maps. Theoretical results aligned with the experimental data, revealing reduced energy gaps, enhanced molecular softness and dipole moments with chain elongation, confirming the impact of alkoxy chain length on mesophase stability.