title: A redox-active porous coordination network film based on a Ru complex as a building block on an ITO electrode.
abstract: The combination of self-assembled monolayer (SAM) and layer-by-layer (LbL) growth methods for the construction of a surface porous film has the potential to incorporate a wide range of chemical functionalities on a solid surface. A novel redox-active Ru complex with 2,6-bis(N-pyridylbenzimidazolyl)-pyridine ligands (Ru complex 1), in which four peripheral pyridine groups act as coordination sites, was used as a building block for a porous coordination network film. By using (4-pyridyl)phenylphosphonic acid as a SAM primer layer on an ITO surface, the Ru complex 1 was immobilized by the successive reaction of PdCl2 on the ITO electrode in the LbL growth method. Multilayer growth was monitored by UV-vis spectra and cyclic voltammetry, in which the linear increases of both absorbance and the peak current were observed. This result indicated that the regular accumulation of Ru complex 1 onto the ITO surface took place. The permselectivity of the present porous coordination network structure was examined using redox-active molecular probes with different sizes and charges such as ferrocene, trimethylaminomethylferrocene, the Os bis(2,6-bis(N-methylbenzimidazolyl)-pyridine) complex, and tetrathiofulvarene (TTF). With the Os complex and cationic ferrocene, only the catalytic peak was observed as a prewave of the adsorbed Ru(II/III) peak at +0.73 V. On the other hand, the oxidation peak of ferrocene was observed around 0 V vs. Fc(+)/Fc even for nine-layered films in addition to the adsorbed Ru(II/III) peak. From these results, not only molecular size but also electrostatic interaction plays an important role in the permeation into the Ru complex 1 porous network film.
authors.affiliation: Department of Applied Chemistry, Faculty of Science and Engineering, Chuo University, 1-13-27 Kasuga, Bunkyo-ku, Tokyo 112-8551, Japan. mhaga@kc.chuo-u.ac.jp.
authors.forename: Takuya
authors.initials: T
authors.lastname: Shinomiya
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Ozawa
authors.forename: Yuichiro
authors.initials: Y
authors.lastname: Mutoh
authors.forename: Masa-Aki
authors.initials: MA
authors.lastname: Haga