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    Langmuir-Blodgett Films of a Clay Mineral and Ruthenium(II) Complexes with a Noncentrosymmetric Structure

    Year: 2002

    Journal: Published on Web 01/19/2002, 20111221

    Authors: Yasushi Umemura, Akihiko Yamagishi, Robert Schoonheydt, Andre Persoons, and Frans De Schryver

    Organizations: Contribution from the Department of Applied Chemistry, National Defense Academy, Yokosuka, Kanagawa 239-8686, Japan, Division of Biological Sciences, Graduate School of Science, Hokkaido University, Sapporo 060-0810, Japan, Center for Interphase Chemistry and Catalysis, K. U. Leuven, Kardinaal Mercierlaan 92, B-3001 Leuven, Belgium, Center for Research on Molecular Electronics and Photonics, K. U. Leuven, Celestijnenlaan 200-D, B-3001 Leuven, Belgium, and Department of Chemistry, K. U. Leuven, Celestijnenlaan 200-F, B-3001 Leuven, Belgium

    Mono- and multilayers of amphiphilic [Ru(phen)2(dcC12bpy)]2+ (phen ) 1,10-phenanthroline, dcC12bpy ) 4,4'-caboxyl-2,2'-bipyridyl didodecyl ester) hybridized with a clay mineral have been prepared by a modified Langmuir-Blodgett method, and their structures and properties have been investigated. Formation of a hybrid monolayer of the Ru(II) complex cations and the clay platelets at an air-clay suspension interface was confirmed by surface pressure-molecular area (Ï€- A) isotherm measurement and atomic force microscopic (AFM) observation. Multilayers were fabricated by depositing the hybrid monolayers onto glass substrates. The absorbance at 492 nm due to the Ru(II) complex cation in the multilayer increased linearly with the increase in the layer number, indicating layer-by-layer deposition of the hybrid monolayers. Because no increase in the second-harmonic generation (SHG) signal from the multilayers against the layer number was observed, the orientation of the Ru(II) complex cations in the layer would be disturbed. The hydrophilic surface of the transferred hybrid monolayer can be converted to a hydrophobic surface by dipping it in an aqueous solution of octadecylammonium chloride (ODAH+Cl-). The multilayers modified with ODAH+ showed a quadratic relation between the SHG intensity and the layer number. This means that the Ru(II) complex cations in the multilayer are successfully oriented in a noncentrosymmetric way by the conversion of the surface property. Both a racemic mixture and an enantiomer of the Ru(II) complex cations were employed to examine the chiral effect on the film properties. The chiral contribution to the SHG signal was enhanced in the multilayer modified with ODAH+.