title: Self-assembly of amphiphilic hexapyridinium cations at the air/water interface and on HOPG surfaces.
abstract: Mono- and multilayers of a novel amphiphilic hexapyridinium cation with six eicosyl chains (3) are spread at the air/water interface as well as on highly ordered pyrolytic graphite (HOPG). On water, the monolayer of 3 is investigated by recording surface pressure/area and surface potential/area isotherms, and by Brewster angle microscopy (BAM). Self-organized tubular micelles with an internal edge-on orientation of molecules form at the air/water interface at low surface pressure whereas multilayers are present at high surface pressure, after a phase transition. Packing motifs suggesting a tubular arrangement of the constituting molecules were gleaned from atomic force microscopy (AFM) investigations of Langmuir-Blodgett (LB) monolayers being transferred on HOPG at different surface pressures. These LB film structures are compared to the self-assembled monolayer (SAM) of 3 formed via adsorption from a supersaturated solution, which is studied by scanning tunnelling microscopy (STM). On HOPG the SAM of 3 consists of nanorods with a highly ordered edge-on packing of the aromatic rings and an arrangement of alkyl chains which resembles the packing of molecules at the air/water interface at low surface pressure. Additional details of the molecular packing were gleaned from single-crystal X-ray structure analysis of the hexapyridinium model compound 2b, which possesses methyl instead of eicosyl residues.
authors.affiliation: Department of Inorganic Chemistry II, University of Ulm, 89081 Ulm, Albert-Einstein-Allee 11, Germany.
authors.forename: Haofei
authors.initials: H
authors.lastname: Gong
authors.forename: Björn
authors.initials: B
authors.lastname: Bredenkötter
authors.forename: Christoph
authors.initials: C
authors.lastname: Meier
authors.forename: Carola
authors.initials: C
authors.lastname: Hoffmann-Richter
authors.forename: Ulrich
authors.initials: U
authors.lastname: Ziener
authors.forename: Dirk G
authors.initials: DG
authors.lastname: Kurth
authors.forename: Dirk
authors.initials: D
authors.lastname: Volkmer