We report experiments by low energy electron diffraction (LEED) and scanning tunneling microscopy (STM) on ordered structures of two sulfur-containing π-conjugated molecules on the Au(111)-surface, namely tetrabenzothianthrene (TBTA) and tetrathiotetracene (TTT). These molecules are candidates for donors in charge transfer salts. On Au(111) both molecules form long-range ordered structures that are commensurate to the top-most surface layer. For TBTA, the reconstruction of the Au(111) surface is maintained, whereas it is lifted by TTT. Both molecules lie flat on the surface. For TBTA, the structure indicates that the molecule is planarized upon adsorption.Highlights► Tetrabenzothianthrene and tetrathiotetracene form long-range ordered commensurate structures on the Au(111) surface ► For TBTA, the reconstruction of the Au(111) surface is maintained. ► The reconstruction is lifted by TTT. ► Both molecules adsorb intact and in a planar configuration. ► For TBTA, the structure indicates that the molecule is planarized upon adsorption.