Electron Transport Dynamics in Redox-Molecule-Terminated Branched Oligomer Wires on Au(111)

• Published in: Journal of the American Chemical Society 2015-01, Vol.137 (2), p.734-741
• Main Authors: Sakamoto, Ryota, Katagiri, Shunsuke, Maeda, Hiroaki, Nishimori, Yoshihiko, Miyashita, Seiji, Nishihara, Hiroshi
• Format: Article
• Language: English
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja509470w

Dendritic bis(ter­pyridine)­iron(II) wires with terminal ferrocene units were synthesized on a Au(111) surface by stepwise coordination using a three-way terpyridine ligand, a ferrocene-modified terpyridine ligand, and Fe(II) ions. Potential–step chronoamperometry, which applied overpotentials to induce the redox of the terminal ferrocene, revealed an unusual electron-transport phenomenon. The current–time profile did not follow an exponential decay that is common for linear molecular wire systems. The nonexponentiality was more prominent in the forward electron-transport direction (from the terminal ferrocene to the gold electrode, oxidation) than in the reverse direction (from the gold electrode to the terminal ferrocenium, reduction). A plateau and a steep fall were observed in the former. We propose a simple electron transport mechanism based on intrawire electron hopping between two adjacent redox-active sites, and the numerical simulation thereof reproduced the series of “asymmetric” potential–step chronoamperometry results for both linear and branched bis(ter­pyridine)­iron(II) wires.