X-ray diffraction study of octylphenyl substituted polytiophenes

Summary form only given. A series of very regular Poly(3-(4-octylphenyl)thiophene)s (POPT), with a varying ratio of monomer to coupling agent (FeCl/sub 3/), and Poly(3-(4-octylphenyl)-2,2´-bithiophene) (POPT/sub 2/) were studied by X-ray diffraction and UV-VIS absorption spectroscopy. The results show that POPT and POPT/sub 2/ are polymers with a low degree of crystallinity, which could be increased by using a more gentle polymerization condition. The diffraction patterns indicate that the polymers, in the amorphous and crystalline phase, pack as relatively straight chains with a long conjugation length as revealed by the absorption spectra. The crystalline structure is formed by planar polymer back-bones stacking on top of each other and the side chains act as spacers between the stacks. This structure resembles closely the one of Poly(3-octylthiophene) (POT), except for the repetition distance along the side chains, which is increased relative to POT by an amount compatible with the space needed for the additional phenyl group. The slight reduction of this repetition distance in POPT/sub 2/ relative to POPT can be accounted for by the increased space available to the side chains.