Orientation of polydiacetylene and poly(p-phenylene ethynylene) films by epitaxy and rubbing

We will focus in this paper on the orientation of thin films of conjugated systems induced either by epitaxy or by rubbing on a polymeric thin layer previously oriented by friction transfer onto glass. In friction transfer, oriented poly(tetrafluoroethylene) (PTFE) onto glass substrates are first prepared, and a layer of the conjugated system is then deposited by vacuum evaporation or by spin-coating. The rubbing technique also enables a mechanical orientation of the thin film of the conjugated system, itself deposited onto glass. We applied both techniques for the preparation of oriented thin films of polydiacetylenes and phenyl-ethynylene oligomers. For an asymmetrically substituted PDA (poly[9(9-carbazolyl)-5,7-nonadiyne-1-ol ethylurethane] (pCNEU), a very high degree of orientation on aligned PTFE was demonstrated using several techniques, resulting in a high degree of orientation than previous films on potassium acid phthalate (KAP) crystals. For the first time a rather good orientation of soluble poly[1,6-bis(3,6-dihexadecyl-N-carbazolyl)-2,4-dexadiyne] (pDCHD-HS) films was obtained using a rubbing technique. Both epitaxy on PTFE and rubbing were also used for the orientation of phenyl-ethynylene derivative samples. For a sequenced rigid polyp-phenylene ethynylene) ester (sPE5C8) fairly good orientations have been obtained.