title: Coverage dependent supramolecular structures: C60:ACA monolayers on Ag(111).
abstract: The dependence of supramolecular structure on fractional molecular coverage has been investigated for acridine-9-carboxylic acid (ACA) and the C(60):ACA binary molecular system. The coverage-dependent phase diagram for ACA is first determined from room-temperature STM imaging. At low molecular coverages (theta < 0.4 ML, ML = monolayer), ACA forms a 2-D gas phase. Ordered ACA structures appear with increasing coverage: first a chain structure composed of ACA molecules linked by consecutive O-H...N hydrogen bonds (theta > 0.4 ML), then a dimer structure composed of ACA dimers linked by paired carboxyl-carboxyl hydrogen bonds (theta approximately equal to 1.0 ML). Structures of the C(60):ACA binary system depend on the coverage of predeposited ACA. At intermediate (0.4 ML approximately 0.8 ML) ACA coverages, C(60) deposition results in a hexagonal cooperative structure with the C(60) periodicity nearly 3 times that of the normal C(60) 2-D packing of 1 nm and exists in enantiopure domains. At higher ACA coverages, a C(60) quasi-chain structure is formed in which parallel C(60) chains are spaced by ACA dimer domains. The mechanistic role of the initial ACA phase in the formation of C(60):ACA supramolecular structures is described. Chemically intuitive molecular packing models are presented based on the observed STM images.
authors.affiliation: Department of Chemistry and Biochemistry, University of Maryland, College Park, MD 20742, USA.
authors.forename: Bo
authors.initials: B
authors.lastname: Xu
authors.forename: Chenggang
authors.initials: C
authors.lastname: Tao
authors.forename: Ellen D
authors.initials: ED
authors.lastname: Williams
authors.forename: Janice E
authors.initials: JE
authors.lastname: Reutt-Robey
mesh_terms: D000166:Acridines / Q000737:chemistry*; D037741:Fullerenes / Q000737:chemistry*; D006860:Hydrogen Bonding; D008567:Membranes, Artificial; D008958:Models, Molecular; D010316:Particle Size; D012834:Silver / Q000737:chemistry*; D013499:Surface Properties
chemical_list: D000166:Acridines; D037741:Fullerenes; D008567:Membranes, Artificial; C522609:acridine-9-carboxylic acid; D012834:Silver; C069837:fullerene C60