Studies of bridge -mediated electron transfer between redox molecules and electrodes

Long-range bridge-mediated electron transfer is a critical element of the mechanisms of many biological superstructures and future electronic technologies. Photosynthesis and cellular respiration are two biological phenomena that utilize bridge-mediated electron transfer in ways that are still not fully understood. The folding and function of certain proteins have also been linked to electron transfer events. The developing field of "molecular-scale" electronics utilizes bridge-mediated electron transfer in several ways, and an improved understanding of the nature of bridge-mediated electron-transfer reactions will be required for such technologies to advance.;Standard electron-transfer rates between immobilized redox-active groups and gold electrodes were measured in five series of ferrocene-based alkanethiolate monolayers on gold. These ferrocenyl alkanethiolates were coadsorbed with nonredoxactive alkanethiolates to dilute the redox-species and structurally support the bridged systems.;Specific examples include: Chapter 2 examines the molecular bridge linking ferrocene to gold consisting of a simple alkane chain (Fc-(CH2) n-SH) or a chain that was modified such that a carboxamide (peptide) linkage replaced the two methylene units directly adjacent to the ferrocene (Fc-CO-NH-(CH2)n-2-SH). Chapter 3 includes a phenoxy linkage (1,3- and 1,4-disubstituted) interposed between the alkanethiol chain and the ferrocene group (Fc-ph-O-(CH2)9-SH). In Chapter 4, the phenyl group was located in the middle of the alkanethiol chain placing a n-butoxy spacer between one of the cyclopentadienyl rings of the ferrocene and the aromatic moiety (Fc-(CH2)4-Oph-O (CH2) 4-SH). It was found that the n-butoxy spacer eliminated the effect of the aromatic moiety and the standard electron-transfer rates measured closely matched that of an alkane bridge with no electronic conjugation. Chapter 5 describes ferrocenyl alkanethiol bridges like the first series (Fc(CH 2)n-SH) buried into the surrounding coadsorbate to study the affect of limiting solvent access to the redox group. Two bridges were selected: a decane thiol bridge with an eicosane thiol (C20-SH) coadsorbate and a dodecane thiol bridge with a docosane thiol (C22-SH) coadsorbate. Finally, in Chapter 6, self-assembled monolayers and ac voltammetry were also applied to the study of ferrocene-tagged, DNA-containing monolayers in an attempt to learn about the surface science of these systems as well as the electron-transfer kinetics of the ferrocene groups attached to the DNA.