Fourier transform Raman spectroscopy of a thiophene solution shows a reduction of aromaticity of the thiophene ring by the interaction with a solvated Lewis acid, which lowers the oxidation potential of the monomer. Low-potential electrochemical deposition of polythiophene was carried out in the presence of a Lewis acid in a solvent with a suitable donor number. High quality conducting polythiophene films were prepared at low potential in BF3-ethyl ether. The conductivity parallel to the film surface is more than 10(4) times that across the film thickness. This anisotropy is related to the orientation of polythiophene chains. The molecular arrangement of polythiophene on a stainless steel electrode was investigated by surface-enhanced Raman scattering and infrared reflection-absorption spectroscopy.