Proton-gated Molecular Devices Based on Rod-shaped Metal Complexes Immobilized on Solid Surface
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Proton-gated Molecular Devices Based on Rod-shaped Metal Complexes Immobilized on Solid Surface Masa-aki Haga,* Youichi Shiozawa, Shinichiro Suzuki, and Miyao Inoue, Integrated Inorganic Material Chemistry Laboratory, Department of Applied Chemistry, Faculty of Science and Engineering, Chuo University, 1-13-27 Kasuga, Bunkyo-ku, Tokyo 112-8551, Japan. E-mail: [email protected] ABSTRACT Rod-shaped dinuclear Ru/Os complexes, [Os(bimpy-X)(BL)M(bimpyH2)]n+( M = Os or Ru; bimpyH2 = 2,6-bis(benzimidazol-2-yl)pyridine,
X = anchoring group such
as disulfide and phosphonic acid, BL =bis tridentate ligand), as a potential candidate for molecular devices have been successfully self-assembled on gold or indium-tin oxide (ITO) electrode by using anchoring ligands.
The Ru/Os assembled complexes on the
solid surface were well characterized by means of MALDI-TOF mass spectrometry, XPS, and electrochemical measurements.
Novel proton-coupled electron transfer
reaction of the self-assembled dinuclear complex on M(bimpyH2) moiety (M = Ru or Os) was confirmed by analyzing the plots of oxidation potential, E1/2, vs pH.
In the
case of M = Os and BL = 1,4-bis(terpyridyl)benzene (btpb), two stepwise one-electron oxidation waves were observed at 0.67 V for the Os(III/II) process and 0.88 V vs Ag/AgCl for the Ru(III/II) process in CH3CN/H2O at pH 1.0.
The E1/2-pH diagram
reveals the intercrossing of Ru(II/III) and Os(II/III) processes at around pH 5.5. Therefore, the intramolecular electron transfer can be controlled by pH.
Proton-
gated electron rectifying effect was observed in this Ru-Os dinuclear complex. INTRODUCTION Proton translocation coupled to redox reaction is often seen in a biological membrane, and the formation of an electrochemical proton gradient plays an important role for the energy transduction such as the production of ATP, active transport or muscle contraction.
Furthermore, current structural studies of bacteriorhodopsin and
cytochrome c oxidase are unveiling the proton-pumping mechanism in the
B5.3.1
biomembrane.[1]
Thus, the combination of proton transfer and electron transfer is
attractive in designing biomimic molecular electronics based on the proton movements. Recently,
We
have
prepared
Ru/Os
complexes
containing
tridentate
bis(benzimidazolyl)pyridine (bimpy-H2) derivatives, which show proton-coupled electron transfer reaction.[2]
Once Ru/Os metal center is oxidized, the remarkable
decrease of pKa value on the N-H benzimidazolyl group in Ru/Os complex induces the release of proton from the complex sphere.
Furthermore, deprotonation of the
intervening benzimidazole moieties appears to induce a large energy perturbation in the dinuclear Ru complexes bridged by 2,2’-bis(2-pyridyl)-bibenzimidazole, and therfore the degree of metal-metal interaction of the deprotonated dinuclear complex becomes 4-6 times larger than that of the protonated complexes.
Furthermore, mixed-valence
tetranuclear RuOs3 complex bridged by bis(benzimidazolyl)bipyridine reveals the proton-induced intra
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