Functional supramolecular structures adsorbed on atomically well-defined surfaces will open new opportunities for the future fabrication of nanoscale devices only when a controlled fabrication process can be achieved. Various approaches can be combined to favorably build a desired functional molecular assembly. A well-established procedure is the tailoring of intermolecular interactions by an appropriate choice of molecular building blocks with suitable and complementary end-group functionalities [1]. Another approach is the use of nanostructured template surfaces exhibiting preferential adsorption sites [2-4]. In principle, the combination of these approaches should allow for the controlled self-assembly of a variety of supramolecular architectures. The challenge, however, is to modify and apply the recipe depending on the targeted specific structure.
We recently reported on the successful fabrication of surface-supported bimolecular wires and ribbons by complementary hydrogen-bonding of the two-fold symmetric 1,4-bis-(4,6-diamino-1,3,5-triazine)-benzene (BDATB) and perylene tetra-carboxylic di-imide (PTCDI) moieties on a vicinal gold template surface [5]. Here we discuss how the co-deposition of a similar, but non-symmetric species affects the self-assembly and leads to significantly different supramolecular structures. By means of scanning tunneling microscopy we have investigated the superlattice structures of single- and bi-component domains formed by BDATB and (4,6-diamino-1,3,5-triazine)-benzene (DATB) on a Au(111) surface. We find that the two closely related DATB and BDATB species phase separate on the surface and self-assemble in different, rather complex supramolecular structures. Co-deposition of PTCDI leads to well-ordered bicomponent superlattices containing either BDATB and PTCDI, or DATB and PTCDI. The structures of these domains present distinct properties. We will discuss the electronic properties of the diverse entities as derived from scanning tunneling spectroscopy.
[1] J. V. Barth et al. Nature 2005 437, 671.
[2] P. Ruffieux et al. J. Am. Chem. Soc. 2007, in press.
[3] W. Xiao et al. J. Phys. Chem. B 2006 110 (43), 21394.
[4] K. Aït-Mansour et al. Phys. Rev. B 2006 74, 195418.
[5] M. E. Cañas-Ventura et al. Angew. Chem. Int. Ed.2007 46, 1814. |