A smectic liquid crystal containing three aromatic units which can be deposited by the LB method

We have synthesised a fumarate ester containing three aromatic rings and studied its properties in the bulk by DSC and other techniques. We have also deposited films of this compound by the LB method and by thermal evaporation in vacuo and characterised multilayers of it by low angle X-ray diffraction. DSC results show that the compound has a crystal to liquid crystal transition at 80°C and a liquid crystal to liquid transition at about 150°C. We have been able to photo-polymerise it while it is in the smectic state. Newly deposited multilayers exhibit clear X-ray diffractograms. However, if the multilayers are annealed at a temperature within the liquid crystalline region, the diffractograms become more clearly defined and the Bragg peaks increase in amplitude indicating an improvement in the coherence length in the direction normal to the plane. We have succeeded in depositing alternate layers of this compound and another compound having liquid crystal properties which we have previously studied. These have been exposed to radiation having a wavelength of 1.064 μm in an attempt to generate the second harmonic but without success. In view of the structure of the compound which has a series of ester bonds, each having an electric dipole moment, we assume that the conformation of the compound is such that these dipoles do not reinforce each others influence as otherwise we would have expected to have observed at least a weak second harmonic signal. Cast films of the compound heavily diluted with an inactive polymer and poled do show some SHG properties.