Chiral Polymorphism: A Scanning Tunneling Microscopy Study

Physisorbed monolayer films of a chiral terephthalic acid derivative have been imaged on highly oriented pyrolytic graphite (HOPG) at the solution−substrate interface using scanning tunneling microscopy. The molecule comprises a nonchiral aromatic moiety and a chiral handle. It is found to form several two-dimensional polymorphs. The packing arrangement of the molecule is primarily directed by the aromatic part, whereas the chiral part may assume different conformations on the graphite surface. The high-resolution data confirm that for all polymorphs molecular chirality is transferred to the two-dimensional adlayer structure in an enantiospecific way. This enantiospecificity is attributed to adsorbate−substrate interactions.