Optically transparent thin layer electrode OTTLE

An optically transparent thin-layer electrode (OTTLE) study18 revealed that the visible spectra of the reduced forms of [Ru(bipy)3]2+ derivatives can be separated into two classes. Type A complexes, such as [Ru(bipy)3]2+, [Ru(L7)3]2+, and [Ru(L )3]2+ show spectra on reduction which contain low-intensity (e< 2,500 dm3 mol-1 cm-1) bands these spectra are similar to those of the reduced free ligand and are clearly associated with ligand radical anions. In contrast, type B complexes such as [Ru(L8)3]2+ and [Ru(L9)3]2+ on reduction exhibit spectra containing broad bands of greater intensity (1,000 [Pg.584]

The other popular approach to in situ spectroelectrochemistry is based on the use of an OTE electrode in a thin-layer, optically transparent thin layer electrode (OTTLE), cell. A schematic representation of one design of OTTLE cell is shown in Figure 2.105. 

In situ photoacoustic spectroscopy has been used to study the redox process on the surface of an electrode using copper metal in alkaline solution.1029 The E° values of copper(II) Schiff base complexes1030 absorbed on optically transparent thin-layer electrodes (OTTLE) have been... 

Figure 3.16A shows spectra of o-tolidine in an optically transparent thin-layer electrode (OTTLE) for a series of applied potentials. Curve a was recorded after application of +0.800 V, which caused complete oxidation of o-tolidine ([0]/[R] > 1000). Curve g was recorded after application of +0.400 V, causing complete reduction ([0]/[R] < 0.001). The intermediate spectra correspond to intermediate values of Eapplied. Since the absorbance at 438 nm reflects the amount of o-tolidine in the oxidized form via Beer s law, the ratio [0]/[RJ that corresponds to each value of Eapplied can be calculated from the spectra by Equation 3.18. 

A vacuum spectroelectrochemical cell that also contains an optically transparent thin-layer electrode (OTTLE) is shown in Figures 18.16 and 18.17. The cell can function either as a spectroelectrochemical cell employing an OTTLE or as an electrochemical cell for voltammetric measurements. This low-volume cell is useful for UV/Vis spectral studies in nonaqueous solvents when the reduction product is sensitive to traces of molecular oxygen present in the solvent. The cell is physically small enough to fit inside the sample compartment of the spectrophotometer. The performance of such a cell was evaluated from visible spectroscopy and coulometry of methyl viologen in propylene carbonate [45]. 

Figure 18.16 Vacuum electrochemical cells (A) vacuum spectroelectrochemical cell that contains an optically transparent thin-layer electrode (OTTLE) and (B) electrochemical cell assembly. [From Ref. 45, with permission.]...

Methods. All solutions were prepared to be ImM Cytochrome c, 0.1mM DCIP, 0.10M alkali halide, and 0.10M phosphate buffer at pH 7.0 or pD 7.0. The DCIP served as a mediator-titrant for coupling the Cytochrome c with the electrode potential. E° values were measured using a previously described spectropotentiostatic technique using an optically transparent thin-layer electrode (OTTLE) (7,11,12). This method involved incrementally converting the cytochrome from its fully oxidized to fully reduced state by a series of applied potentials. For each potential a spectrum was recorded after equilibrium was attained. The formal redox potential was obtained from a Nernst plot. The n value... 

Figure 28. Configurations for spectroelectrochemistry. A) optically transparent electrode B) optically transparent thin-layer electrode (OTTLE) C) Internal reflection spectroscopy, and D) specular reflectance spectroscopy.

Other spectroscopic techniques that have been used with electrochemistry to probe nanoparticles include electronic and vibrational spectroscopies. The spec-troelectrochemistry of nanosized silver particles based on their interaction with planar electrodes has been studied recently [146] using optically transparent thin layer electrodes (OTTLE). Colloidal silver shows a surface plasmon resonance absorption at 400 nm corresponding to 0.15 V vs. Ag/AgCl. This value blue shifts to 392 nm when an Au mesh electrode in the presence of Ag colloid is polarized to —0.6 V (figure 20.12). The absorption spectrum is reported to be quite reproducible and reversible. This indicates that the electron transfer occurs between the colloidal particles and a macroelectrode and vice versa. The kinetics of electron transfer is followed by monitoring the absorbance as a function of time. The use of an OTTLE cell ensures that the absorbance is due to all the particles in the cell between the cell walls and the electrode. The distance over which the silver particles will diffuse has been calculated to be 80 pm in 150 s, using a diffusion coef-... 

The particular advantage of this optically transparent thin-layer electrode (OTTLE) is that bulk electrolysis is achieved in a few seconds, so that (for a chemically reversible system) the whole solution reaches an equilibrium with the electrode potential, and spectral data can be gathered on a static solution composition. 

ABTS + production has been described by using thin-layer spectroelectrochemistry [46]. Fifty microliters of ABTS in 0.1 M acetate buffer solution (pH 5) was oxidized in a quartz flat cell (0.1 cm width) containing an optical transparent thin-layer electrode (OTTLE system). The radical formation was measured with a potential scan from 0.65 to 0.70 V and returned to 0.65 V at the scan rate of 0.05 mV s . The reactions were monitored spectrophotometrically every 30 s. Figure 31.11 shows the 3D plots obtained for spectral changes during ABTS electrolysis at different intervals. At the beginning, with ABTS as the sole species, two peaks were observed (A = 214 nm, A.2 = 340 nm), but as the... 

Figure 1 shows absorbance spectra, for a series of applied potentials, recorded in an electrochemical cell employing an optically transparent thin-layer electrode (OTTLE). Curve a was recorded after application of -1-0.800 V vs saturated calomel electrode (SCE), which under thin-layer electrode... 

Figure 1 Schematic diagram of spectroelectrochemical techniques at an optically transparent electrode (OTE). (A) Transmission spectroelectrochemistry (B) transmission spectro-electrochemistry with an optically transparent thin-layer electrode (OTTLE) cell (C) internal reflection spectroscopy (IRS). Reprinted by courtesy of Marcel Dekker, Inc. from Heineman WR, Hawkridge FM and Blount HN (1984) Spectroelectrochemistry at optically transparent electrodes. II. Electrodes under thin-layer and semi-infinite diffusion conditions and indirect coulometric titrations. In Bard AJ (ed) Electroanalytical Chemistry. A Series of Advances, Vol 13, pp 1-113. New York Marcel-Dekker.

Figure 5 Optically transparent thin-layer electrode (OTTLE) cell (A) front view (B) side view, (a), Point of suction application to change solution (b) Teflon tape spacers (c) microscope slides (1x3 in.) (d) solution (e) transparent gold minigrid electrode (f) optical path of spectrometer (g) reference and counter electrodes (h) solution cup. Epoxy resin holds the cell together. Reprinted with permission from DeAngelis TP and Heineman WR (1976) Journal of Chemical Education 53 594-597. 1976 American Chemical Society.

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