In this work we report on STM and LEED investigations of donor-acceptor-substituted bi- and terthiophene monolayers on weakly interacting substrates prepared under two different conditions: by evaporation in UHV and by adsorption at the liquid/solid interface. A detailed comparison of the results shows that the ordering is mainly given by the intermolecular interactions, but the observed molecular structures can also depend on the specific preparation conditions. In all cases the orientation with respect to the substrate is strongly influenced by the environment. At the liquid/solid interface the molecule-substrate interaction seems to be reduced by the solvent, leading to close-packed structures with no phase relation with respect to the substrate, whereas for UHV-prepared monolayers well-defined azimuthal orientations were found.