| Abstract
| - Parallel-displaced π−π stacking interactions have been known to be the dominant force in stabilizing the doublehelical structure of DNA and the tertiary structure of proteins. However, little is known about their roles in self-assembled monolayers of other large π molecules such as aromatic thiols. Here we report on a systematic study ofthe self-assembled monolayers of four kinds of anthracene-based thiols, 9-mercaptoanthracene (MA), (4-mercaptophenyl)(9-anthryl) acetylene (MPAA), (4-mercaptophenyl) (10-nitro-9-anthryl) acetylene (MPNAA), and (4-mercaptophenyl)(10-carboxyl-9-anthryl) acetylene (MPCAA) on Au(111), in which a spacer and different functional groups (NO2 andCOOH) are intentionally designed to introduce and thus allow the investigation of various intermolecular interactions,in addition to π−π interactions in the base molecules. We find that all molecules form long-range-ordered monolayersand, more interestingly, that these assembled monolayers exhibit essentially the same fundamental packing structure.On the basis of high-resolution scanning tunneling microscopy observations, we propose the space-filling models forthe observed superstructures and demonstrate that all superstructures can be understood in terms of the parallel-displaced π−π stacking interactions, despite the presence of competing dipole−dipole and H-bonding interactionsassociated with these specially designed functional groups.
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