X-RAY-DIFFRACTION STUDIES OF IODINE-DOPED POLY(3-ALKYLTHIOPHENES)

The structural evolution during iodine-vapor doping of various poly(3-alkylthiophenes) has been studied by in situ x-ray diffraction. Equatorial and non-equatorial diffraction data are presented. Dopant-ion diffusion into the polymer host matrix induces cooperative motions of both the thiophene backbone and alkyl side chains with dramatic variations in the lattice spacings perpendicular to the polymer chain axis. This evolution is found to be sensitive to the specific length of the alkyl side chains. Hexyl and octyl substituted samples undergo continuous changes within a single ''homogeneously-doped'' structure while poly(3-dodecylthiophene) samples exhibit a region of two-phase coexistence. These experimental results are presented in combination with structure factor calculations of suggestive models that identify key structural features of the guest-host composite.