Synthesis and physico-chemical properties of dilateral flouro azo/ester four aromatic ring mesogens and their mixtures of liquid crystals

Four series of di-flouro, namely; 4-substituted phenylazo-3-flouro phenyl-4′-n-alkoxy 3-flouro phenylazo benzoates (Ina-d) based on aromatic rings with the azo/ester/azo linkages core, were prepared and investigated for their mesomorphic properties. An alkoxy group with chain length varied from n = 6 to 16 is attached to the terminal phenylazobenzoate moiety and the other terminal is a compact group (X = –CH3O, –CH3, H and Br) attached to phenylazo moiety. The mesophases were investigated by DSC and POM and compared with previously investigated dilaterally methyl substituted analogues. Terminally unsubstituted and Br substituted analogues displayed dimorphic N and SmA phases, except the lower homologue (n = 6), while terminally – CH3O analogues exhibited monomorphic N phase. For terminally – CH3 substituted, compounds with n = 6–12 exhibited only N phase, while compounds with n = 14 and 16 displayed N and SmA phases. Meanwhile, the dilateral F substituents result in an enhancement in clearing thermal transitions compared with dilateral methyl substituents with a wide mesophase range. TGA analysis revealed that the prepared compounds are thermally stable within mesophase temperature range, except – CH3O, –CH3 and Br derivatives with n = 6. Binary mixtures of I6a-d/I16a-d derivatives were investigated. The photo-physical property was also studied.