Some Properties and Methods of Preparation of Thin Solid Anisotropic Organic Films
Thin films of coronene (Cor) were prepared by PVD. These films of thickness from 0.8 to 0.2 µm show microcrystalline aggregate structure which changes upon annealing in vacuum. Electrical conductivities perpendicular and parallel to the surface of the thin film are of the order of 10-8 ohm-1cm-1 showing small anisotropy. After iodine doping conductivity of Cor film increases by six orders of magnitude. The electrical properties of the investigated Cor thin layers were compared with the data for super-lattices of linear acenes. Two methods of oriented films preparation elaborated by us are presented. The first consists in obtaining oriented thin layer of lyotropic liquid crystalline cellulose derivative hydroxypropylcellulose (HPC) solution in acrylic acid (AA) by shearing. The rapid photopolymerisation of AA fixes the orientation in solid film. Thin films doped with dichroic dyes show an orientation of dopant depending on HPC and dye concentration. The second technique called zone casting consists in deposition of a solution of crystallizable component and polymer from a flat nozzle on moving support. The oriented crystallization occurs in the meniscus while the solvent evaporation and solidification of the film occurs. This method was applied to obtain highly optically and electrically anisotropic long flat ribbon-like CT complexes crystals in polymer matrices. This technique after refinement was also used for preparation of solid thin films substituded hexa-peri-benzocoronene (HBC-C12). The obtained very thin films exhibit high orientation of columnar structures of HBC-C12.