THE EFFECT OF STEREOREGULARITY ON THE STRUCTURE OF POLY(OCTYLTHIOPHENE) - AN X-RAY-DIFFRACTION STUDY

The structural properties of soluble Poly(3,3'-dioctyl-2,2'-bithiophene) (PDOBT), a stereoregular analogous of Poly(3-octylthiophene) (POT), have been studied by X-ray diffraction and UV-VIS absorption spectroscopy. The absorption spectra have been acquired in the temperature range 20-170 degrees C. The results show that PDOBT is partial crystalline with the polymer chains packing in a parallel manner. The well defined head-to-head, tail-to-tail arrangement of the monomer units along the polymer chain leads to a crystalline structure differing consider ably from the one of POT. Adjacent head-to-head coupled thiophene rings are twisted out of plane, leading to a short conjugation length as manifest by the absorption maximum, which is blueshifted relative to POT. In contrast to POT, PDOBT does not show any thermochromic effect. This agrees with our new structural model for PDOBT.