Adsorption-induced distortion of a largeπ-conjugated molecule studied bysurface $\rm X$-ray diffraction: End-capped quaterthiophene on $\textmd{Ag(111)}

The internal geometric structure of a large π-conjugated organic molecule adsorbed on a metallic surface (end-capped quaterthiophene on Ag(111)) was determined in detail by using surface X-ray diffraction. In contrast to the common belief that such molecules remain undistorted on a weakly interacting substrate, we find significant distortion of the thiophene rings and elongation of the bond distances. These results open new perspectives for the understanding of large organic adsorbates and have important implications for a deeper insight into organic/inorganic interfaces in general.