ER Measurements for Redox-active Thin Organic Films

The instrumentation shown in Fig. 2.4 enables us to detect a change in the reflectance of the order of 10 of the total reflectance at a metal electrode at /= 14 Hz with a lock-in ampHfication time constant of 3 s. 

In another configuration of instmmentation, irradiation of white light onto the electrode surface and detection of reflected light by the use of a multi-channel detector (such as CCD or photo-diode array) through a grating monochromator makes multi-channel measurement possible [21]. 

ER Measurements for Redox-active Thin Organic Films 

In this section, we are concerned with a mirror-like electrode surface covered with a redox-active thin organic film. Assume that the redox interconversion of the species in the film causes detectable change in the optical properties. In particular, at least one of the compound s oxidation states (both or either of the reduced and oxidized forms) exhibits optical absorption. We first assume that the reflectance at the modified electrode is a linear (first-order) function of the superficial fraction of a chromophore in a given oxidation state. Note that this assumption does not necessarily have a strict rationale in optical theory. We will later return to this point and reconsider it. 

The redox active film of interest is assumed to undergo electrochemically reversible interconversion between oxidized and reduced states as a function of electrode potential as described by the Nernst equation. If so, then the plot of reflectance Rdc as a function of the electrode potential E can be represented schematically as Fig. 2.5. When AFac-C R77 appT. the linear response approximation is valid A sine wave potential modulation should give rise to a sinusoidal change of the reflectance, as shown in Fig. 2.5, where R is the gas constant, T is the absolute temperature, app is the apparent number of electrons involved in the redox equilibrium relationship, and F is the Faraday constant. 

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ER Measurements for Redox-active Thin Organic Films I 59... 

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