Synthesis and Proton-Coupled Electron-Transfer Reaction of Self-Assembled Monolayers of a Ruthenium(II) Complex Containing Tridentate 2,6-Bis(benzimidazol-2-yl)pyridine on a Gold Surface:  Comparison of Acid/Base Chemistry with Bulk Solution Chemistry

Abstract

The self-assembly and electrochemical properties of a novel Ru(bimpyH2) complex functionalized by disulfide on a polycrystalline gold electrode (bimpyH2 = bis(benzimidazol-2-yl)pyridine) were characterized by means of MALDI-TOF mass spectrometry, XPS, and cyclic voltammetry. The Ru complex monolayers exhibit a quasi-reversible Ru(III/II) oxidation at +0.66 V vs SCE in 0.1 M HClO4 aqueous solution. The shape of the cyclic voltammograms for Ru(III/II) couple is strongly dependent on the surface coverage, and is close to the ideal voltammogram when the Ru neat monolayers are diluted by octanethiol. The oxidation potential of the Ru complex mixed monolayers with octanethiol shows a linear dependence on solution pH, indicating that the proton-coupled oxidative reactions occurred on the gold surface. The pK a values for the Ru mixed monolayers on the gold surface were obtained as pK a1 = 6.0 and pK a2 = 7.8 for the Ru(II) state and ∼1.5 and 3.4 for the Ru(III) state from the E 1/2−pH plots. The pK a values of the Ru(bimpyH2) group on the gold surface are a little smaller than those of [Ru(dmbimpy)(bimpyH2)]2+ (dmbimpy = bis(1-methylbenzimidazol-2-yl)pyridine) in the bulk solution. These disulfide-functionalized Ru(bimpyH2) complex monolayers on the gold surface can act as an electrochemical pH probe on the surface.

Proton‐Coupled Electron‐Transfer Processes in Ultrafast Time Domain: Evidence for Effects of Hydrogen‐Bond Stabilization on Photoinduced Electron Transfer

“…[16,17] Hammarstrçm and co-workersr eported an intramolecular PCET process that occurred in the micro-a nd nanosecondt ime domain for ruthenium-tyrosine and tryptophan complexes involving electron transfer from tyrosine and tryptophan to the oxidized Ru center,a nd the water molecule participated in the process as ap roton acceptor. [16,17] Hammarstrçm and co-workersr eported an intramolecular PCET process that occurred in the micro-a nd nanosecondt ime domain for ruthenium-tyrosine and tryptophan complexes involving electron transfer from tyrosine and tryptophan to the oxidized Ru center,a nd the water molecule participated in the process as ap roton acceptor.…”

“…Haga and co-workers reported some imidazole-functionalized Ru II -polypyridyl complexes immobilized on ag olds urface; these showed the PCET phenomenona nd the process was studied through cyclic voltammetry. [16,17] Hammarstrçm and co-workersr eported an intramolecular PCET process that occurred in the micro-a nd nanosecondt ime domain for ruthenium-tyrosine and tryptophan complexes involving electron transfer from tyrosine and tryptophan to the oxidized Ru center,a nd the water molecule participated in the process as ap roton acceptor. [18,19] Costentin et al discussed the mechanistic aspects of PCET with phenol in the proton relay networks.…”

Ruthenium–amine complexation for constructing self-assembled molecular films

“…Complex SAMs consisting of metal ions and aminosilane molecules are expected to show electrochemical activities. In particular, SAMs with ruthenium (Ru) ion complex centers are attractive, since such monolayers show excellent redox reversibility and optical functions [32][33][34][35][36].…”

Packing effects in 4,4′-bis(4-hydroxybutyl)-2,2′-bipyridine and 4,4′-bis(4-bromobutyl)-2,2′-bipyridine

“…Compounds containing 2,2 H -bipyridine (bpy) substituted at the 4,4 H -positions with alkyl chains of different lengths are interesting precursors for functionalization with thiols, carboxylic acids, disul®des or other anchoring groups. Compounds with such terminating groups have displayed the potential to form a self-assembled monolayer on metallic or semiconducting surfaces (Bain, Troughton et al, 1989;Haga et al, 2000;Bain, Biebuyck & Whitesides, 1989;Vogelson et al, 2003). Interestingly, bpy substituted with alkyl groups at the 4,4 H -positions has been used as a covalent link in porphyrin±RuO 2 clusters, and the in¯uence of the linking alkyl chain length on the photoinduced intramolecular electron transfer in such clusters has also been studied (Resch & Fox, 1991).…”