Redox ER signal

Estimation of the Molecular Orientation on the Electrode Surface using the Redox ER Signal... 

Let us consider the ER signal due to the redox reaction of a surface-confined dye molecule. For simplicity, we assume that, for an electrode/adsorption layer incorporating a chromophore/solution interface, the absorption of the oxidized form is negligibly small, i.e. the oxidized form is colorless. We also assume that the electric dipole moment of the reduced form is of a single hnear dipole and that it has a unique director angle f with respect to the surface normal while its azimuthal angle is two-dimensionally isotropic (Fig. 2.15a). The angle

director vector with respect to the surface normal represents the molecular orientation. 

When a redox reaction is only the origin of the ER signal and the change of reflectance is directly proportional to the amount of the redox couple intercon-verted between oxidized and reduced state, Rac can be written [9, 56, 69] as... 

We now use an equivalent circuit representing an electrode/solution interface where the electrode surface is covered by an electroactive monolayer. The simplest circuit is shown in Fig. 2.18. We assume that the molecules in a Langmuir monolayer undergo an n-electron transfer reaction in response to ac and that the ER signal is exclusively due to this faradaic process [69]. The faradaic process of the surface-confined species at the formal potential is represented by a series connection of a constant capacitance associated with the redox reaction of the adsorbed species Q and a charge transfer resistance Ret. where Q is written for a Nernstian process as... 

Fig. 2.21 An equivalent circuit representing an electrode/solution interface, where the electrode surface is covered by a monolayer of a redox active species, used to explain the combined analysis of ac impedance and ER signal. Zj impedance representing the doublelayer charging process.

In the previous subsection, the analysis of an ER signal in a frequency domain is restricted to the use of the experimental signal at the formal potential of the redox reaction of interest If we can take a similar approach using the potential... 

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