Structural aspects of oriented poly(octylphenylthiophene) studied in bulk and sub-micron layers by X-ray diffraction

Abstract The structural properties of poly(3-(4-octylphenyl)thiophene) (POPT) in bulk solution-cast films and in ultra-thin spin-cast films were studied by X-ray diffraction. The structural aspects associated with an induced colour change of the spin-cast films are highlighted. In bulk form POPT is partial crystalline and is characterized by a lamellar structure in which stacks of planar thiophene main chains are uniformly spaced by the octylphenyl side chains. The polymer is preferentially oriented with the side chains normal to the substrate surface. The crystal structure resembles that of poly(3-octylthiophene), although the lattice parameters along the side chains (α-axis) and along the stacking direction ( b -axis) are larger in POPT. The ultra-thin (sub-micron) spin-cast films, on the contrary, are essentially amorphous, but exposure to chloroform vapour and/or heat leads to an increase of crystallinity, paralleling a red shift of the absorption spectrum.