Single-Molecule Electron Transfer in Electrochemical Environments

Abstract

where he has worked since 1993. He received his Ph.D. in Solid State Physics in 1982 and his D.Sc. in Theoretical Physics in 1998. His research covers solid state physics, the physics of liquids, theory of adsorption, many-particle physics and the theory of electrochemical electron transfer. His present research is focused on the theory of electron tunneling in bridged electrochemical contacts. He is the author or co-author of more than 60 publications in scientific journals. Qijin Chi received his Ph.D. degree in analytical and physical chemistry in 1994 from the Changchun Institute of Applied Chemistry, Chinese Academy of Sciences. After having spent one year as a DFG postdoctoral fellow at Tübingen University, Germany, and two years as a JSPS postdoctoral fellow in Tokyo, Japan, he joined the Department of Chemistry at Technical University of Denmark in 1998. He is currently a lektor (associate professor) in chemistry. Qijin Chi also studied molecular biology and biochemistry (2000-2003) at the Johns Hopkins University School of Medicine. His research interests include biological nanomaterials, electrochemistry, surface self-assembled chemistry, and biophysics. He has authored four patents, over fifty research articles, and several book chapters. Tim Albrecht graduated in chemistry at the University of Essen in 2000. He received a Ph.D. with Prof. P. Hildebrandt at the Max-Planck Institute for Radiation Chemistry (now Bioinorganic Chemistry) in Muelheim/ Germany for studies on interfacial charge transfer processes of heme proteins using spectroelectrochemistry (SE(R)RS) and electrochemical STM. He held a Marie-Curie fellowship 2004-2006 whilst working in Prof. J. Ulstrup's group and became a lecturer in Physical Chemistry at Imperial College London in 2006. His research interests include (bio)electrochemistry, charge transport through individual molecules, and electrode/nanopore architectures in single-biomolecule sensing. He has published 14 research articles, 2 book chapters, and filed 2 patent applications. Palle Skovhus Jensen obtained his M.Sc. degree in 2006 at Technical University of Denmark and is presently a Ph.D. student in Prof. J. Ulstrup's group. His research includes interfacial electrochemistry, electrochemical STM and AFM of redox metalloproteins, extending to catalysis of bioelectrochemical processes by molecular scale metallic nanoparticles. He is the co-author of several research articles in these areas.

Single-Molecule Electrochemical Gating in Ionic Liquids

“…The parameters γ and ξ are, however, correlated in the narrow tunneling gap in which the Debye length, L d is comparable to the tunneling gap width L. The precise form of this correlation is not presently known for ionic liquids, but as an illustration, the correlation takes the following form for ionic solutions (say, aqueous solution) in the Debye−Huckel limit 29,32,66 …”

“…Other single-molecule systems studied with electrochemical gating and the in situ BJ or I(s) techniques have included oligophenylene-ethynylenes, 16 various perylene tetracarboxylic diimide derivatives, 17,18 oligo-anilines, 19−21 and a pyrrolo-tetrathiafulvalene (pTTF) derivative, 22 while systems studied by electrochemical STS include transition metal complexes, 23−27 viologens, 13,15 and redox metalloproteins. 28,29 Electrochemical gating has also been achieved in mechanically controlled break junctions. 30 Both the in situ electrochemically gated molecular break junction and electrochemical STS configuration can be modeled in terms of the redox active moiety positioned within the nanogap between the metal electrode substrate and metal STM tip.…”

“…In the electrochemical scanning tunneling spectroscopy configuration (i.e., STM tip not chemically attached to the molecule) there is now a collection of examples displaying a clear maximum in their tunneling current (I tunneling ) vs electrochemical potential relations. 13,15,[23][24][25][26][27]29,39 These have been well-modeled in terms of the KU relationship for two-step electron/hole transfer through the redox center in the STM−substrate gap. The situation is far from clear for measurements made in the in situ electrochemically gated BJ configuration (i.e., when the electrochemically active bridge molecule is chemically attached at one end to the STM tip and at the other end to the substrate).…”

Electrochemical Control of Single-Molecule Conductance by Fermi-Level Tuning and Conjugation Switching

“…Conductance switching in molecular junctions has been demonstrated previously using various means including light, 1, 2 bias pulses, 3 electrostatic-, 4,5 and electrochemical gating. 6,7 The concept of "electrochemical gating" which provides the opportunity to overcome the technical challenges of incorporating a gate electrode in a solid-state molecular device, has been employed in electrochemically active molecular systems, including viologens, [8][9][10] oligoaniline, 11 ferrocene, [12][13][14] transition metal complexes, 7,15,16 perylenebisimides, [17][18][19] redox-active proteins, 20,21 quinones 22,23 and tetrathiafulvalene, 24 as well as redox-inactive molecules. 25 In the case of redox-inactive molecules, or more generally when the electrode potential does not overlap with the molecule's redox potential, the effect of the gate is simply to shift the molecular levels up or down in energy relative to the Fermi level.…”

Direct measurement and modulation of single-molecule coordinative bonding forces in a transition metal complex

“…In the past two decades, the scanning probe microscopies have, however, increasingly enabled nontraditional and single-molecule approaches to physicochemical properties of many important chemical and biological processes 3 , ranging from electron transfer (ET) [4][5][6] and molecular recognition 7,8 to in vivo biochemical processes in a living cell 9 . In terms of transition metal complexes, scanning tunnelling microscopy (STM), particularly electrochemical STM (ECSTM), as an advanced tool has offered detailed mapping of single-molecule conductivity patterns in chemical or/and electrochemical environments [10][11][12][13] .…”