Impact of fluorine orientation on the optical properties of difluorophenylazophenyl benzoates liquid crystal

The orientation effect of two laterally fluorine atoms on the optical properties of difluoro substituted-4-(2'-(or 3'-) fluorophenylazo)-2-(or3-) fluoro phenyl-4″-dodecyloxybenzoates thermotropic liquid crystals (I & II) were investigated. The compounds (I, II) were dissolved in methylene chloride in order to detect its absorption and transmission in UV-visible region at room temperature. The maximum absorption for the compounds was in the blue visible region (440-445 nm). The phase transition temperature by using DSC, POM and spectrophotometer techniques was investigated at variable temperatures for the compounds used. Nematic phase was observed for compound I during heating and cooling processes when the two fluorine atoms directed towards the molecular core while the smectic phase appears when the two atoms directed outward the molecular core. Refractive indices, birefringence, order parameters and thermal stability factors for compounds I and II were measured. Birefringence values of compounds I & II, reached 0.32 and 0.22 for nematic and smectic phase respectively.