Monolayers electron transfer rate

Z.Q. Feng, S. Imabayashi, T. Kakiuchi, and K. Niki, Electroreflectance spectroscopic study of the electron transfer rate of cytochrome c electrostatically immobilized on the w-carboxyl alkanethiol monolayer modified gold electrode. J. Electroanal. Chem. 394, 149-154 (1995). 

Figure 6. Structural formulae of S-D amphiphilic compounds and other chemicals used for S-D monolayers for comparison of photo-induced electron transfer rates between a single alkyl chain and a triple alkyl chain as the spacers of the S-D dyads with the same length of four-carbons. In these S-D dyads, a naphthalene and a ferrocene moiety are used as an S and a D moiety, respectively. S-D dyads with a rigid spacer consisting of a bicyclo[2.2.2]octane are used as dyads with a triple alkyl chain.

The transfer of the stable monolayers onto substrate plates and the comparison of the photoinduced electron transfer rates between S-D dyads with a rigid and a single alkyl chain spacer is now under investigation. 

The first exponential term in both equations is independent of the applied potential and is designated as k and A(L for the forward and backward processes, respectively. These represent the rate constants for the reaction at equilibrium, e.g. for a monolayer containing equal concentrations of both oxidized and reduced forms. However, the system is at equilibrium at E0/ and the products of the rate constant and the bulk concentration are equal for the forward and backward reactions, i.e. k must equal Therefore, the standard heterogeneous electron transfer rate constant is designated simply as k°. Substitution into Equations (2.19) and (2.20) then yields the Butler-Volmer equations as follows ... 

Electrodes represent an unrivaled platform onto which interfacial supramolecular structures can be assembled. They can be fully characterized before assembly and offer a convenient means to both probe and control the properties of the film. The interest in this area has increased dramatically in recent years because adsorbed monolayers enable both the nature of the chemical functional groups and their topology to be controlled. This molecular-level control allows the effects of both chemical and geometric properties on electron transfer rates to be explored. Moreover, these assemblies underpin technologies ranging from electrocatalysis to redox-switchable non-linear optical materials. 

Figure 5.2 Tafel plots of In k versus overpotential for a mixed self-assembled monolayer containing HS(CH2)i600C-ferrocene and HS(CH2)isCH3 in 1.0 M HCIO4 at three different temperatures V, 1 °C O/ 25 °C , 47°C. The solid lines are the predictions of the Marcus theory for a standard heterogeneous electron transfer rate constant of 1.25 s-1 at 25 °C, and a reorganization energy of 0.85 eV (= 54.8 kj moh1). Reprinted with permission from C. E. D Chidsey, Free energy and temperature dependence of electron transfer at the metal-electrolyte interface, Science, 251, 919-922 (1991). Copyright (1991) American Association for the Advancement of Science...

The electron transfer dynamics of monolayers based on osmium polypyridyl complexes linked to an electrode surface through conjugated and non-conjugated bridges, e.g. frans-l,2-bis(4-pyridyl)ethylene (bpe) and 1,2-bis(4-pyridyl)ethane (p2p), respectively, have been explored [18]. The standard heterogeneous electron transfer rate constant, k°, depends on both a frequency factor and a Franck-Condon barrier, as follows [19-21] ... 

Photoisomerization of the monolayer to the c/s-azobenzene configuration removes the threaded Fc- i-CD to a spatially separated position which retards the electron transfer rate. Therefore, the assembly functions as a molecular optoelectronic system which records optical information and transduces it into an electronic signal. 

As discussed earlier, SAMs of alkanethiols on gold surfaces offer access to highly ordered, surface-confined molecular structures. The use of these assemblies as stable, well-defined spacers for studies of electron transfer between the gold electrode and redox eenters attached to the film surface [50, 73-83] or in solution [44, 46, 84] is depicted in Figure 5. The densely packed monolayer maintains a precise separation between a gold electrode surface and the pendant or dissolved redox center, and effectively eliminates conformational mobility that can complicate electron-transfer rate studies [73]. An advantage of using electrode-confined spacers is that... 

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