Comparative structures of thiophene oligomers

Using X-ray diffraction and electron microscopy, we have examined the structures of specially synthesized, highly purified oligomers of poly(thiophene) that show exceptionally high semiconductor mobilities and current on/off ratios. The tetramer, hexamer, and octamer all show the same planar conformation and herringbone-type molecular packing as has been determined earlier for the hexamer (alpha-6T) through detailed analyses, Thin films evaporated onto Si substrates for device applications also show the same morphologies (consisting of irregular grains less than or equal to 100 nm in diameter) and molecular orientations (essentially perpendicular to the substrates).