Electrochemical redox potentials

Based on correlations between energy level positions and electrochemical redox potentials, it has been estabHshed that polymethine dyes with reduction potentials less than —1.0 V (vs SCE) can provide good spectral sensitization (95). On the other hand, dyes with oxidation potentials lower than +0.2 V ate strong desensitizets. 

If a scale of electrochemical redox potentials is considered, it is obvious that water is not an easily oxidizable species nor is carbon dioxide easily reduced. The energy requirement of photosynthesis in green plants can be met only by the cooperation of two excited chlorophyll molecules. The first one gives a part of its excitation energy to the second one (Figure 5.4). 

The electrochemical redox potential of several possible decomposition reactions at pH = 0 (relative to the potential of the saturated calomel electrode), which have been estimated from thermodynamic parameters (6,17-21), are shown schematically in Figure A. The band levels are shown for open-circuit conditions. The standard electrode potentials were calculated from the free energies of formation, which are summarized below in Table III. 

Ionic potential — Function defined by = zjr, where z and r are the valence and radius of an ion, respectively. This function was introduced by G.H. Cartledge [i,ii], who used it as a quantitative basis of the periodic classification of elements. The ionic potential is directly connected with the heat of hydration of ions (see - Born equation), and thus related to the heat of solution of salts, acidic properties of ions, and others. It is also known that the ionic potential is correlated with electrochemical redox potentials (e.g., for solid metal hexacyanomet-allates [iii]). 

Table 3 Electrochemical Redox Potentials of TTF Under Different Experimental Conditions...

Table 4 Electrochemical Redox Potentials of Tetrachalcogenotetracenes 13 (R = H) and Tetraselenaperylenes 18 and 19...

Table 5 Electrochemical Redox Potentials of Electron-Rich Tetrasubstituted Ethylenes3...

Table 9 Electrochemical Redox Potentials for Derivatives Containing Two TTF Moieties...

Table 10 Electrochemical Redox Potentials of Some Common Organic ir-Electron Acceptors3...

The rednctive electrochemistry of several Ni complexes of unsaturated dithiolate ligands has been examined. On the basis of the electrochemical redox potentials, EPR spectral evidence, and SCF calculations, these rednction products are best formulated as Ni complexes for dithiocarbamate and 1,2-dithiolene hgands, and as Ni stabihzed ligand-radical anions for dithiodiketonate species. It is often difficnlt to assign electron-density distributions within a molecnle, particnlarly with delocahzed hgands such as dithiolenes. 

Some 60 dyes have been selected as possible photovoltaic materials their electrochemical redox potentials, surface adsorption, spectroscopic properties, fluorescence yields, and acid-base properties have been measured. The aim of this work is to produce a low-cost panel for harvesting solar energy as electrical power. The physical principles of fluorescent solar collectors have been discussed by Raue and Harnisch and several classes of dyes examined. Coumarin dyes are suitable convertors, particularly if the amino-group is fixed by ring closure to the aromatic system. 

Small metal particles on the nanometer dimension are of particular interest regarding their solid-state properties as well as their important application as catalysts. Such particles offer a useful model allowing the study of structural effects with relevance for a variety of applications in chemistry and physics. The key point of interest lies in the fact that such particles often possess very different and sometimes novel properties compared to those of bulk materials, i.e., their physical properties (spectroscopic, electronic, magnetic) differ from those of the bulk phase and are particle size-dependent [68]. One such property concerns the variation in the electrochemical redox potential between metals in a dispersed and bulk state, as was shown by Plieth [69], when he demonstrated that the redox potential depended on the radius (r) of a metal particle on nanometer dimension (the radius was assumed to vary from 1 to lOnm) according to the following equation ... 

In the non-adiabatic limit, the total ET rate can be expressed as the sum of ET rates to all possible accepting states in the semiconductor (Marcus, 1965 Gao et al, 2000 Gao and Marcus, 2000 Gosavi and Marcus, 2000). For electron injection from an adsorbate excited state with electrochemical redox potential of U°(S /S ) to a semiconductor k state at e = E- Ecb) above the band edge (with flatband potential of U°cb), the reaction can be written as... 

The sources of data in Table VII.8 are quite diverse. The value proposed by Reiss and Heller [101] resulted from electrochemical redox potential measurements involving the absolute potential of the standard hydrogen electrode, a type of measurement that requires some assumptions, since just... 

The above discussions clearly demonstrates the importance of 6-pyrrole brominated porphyrins in both fundamental and applied fields of porphyrin chemistry. While one aim of these studies has been to gain insights into the role of macrocycle distortion in relation to biological systems containing porphyrins or related macrocycles , another has been to determine which factors influence the robustness of such catalysts in the oxidation of organic substrates ". Both measurements of electrochemical redox potentials and spectral properties of the porphyrins are needed to understand these properties and both are reviewed in this chapter on yS-pyrrole brominated porphyrins. 

Study of the ECL based on Ru(bpy)3 revealed that luminescence intensity of monohydric alcohols decreased as alkyl chain length of the molecules increased while increase in the number of hydroxyl groups in a molecule leads to enhancement in limiinescence intensity for polyhydric alcohols [120]. Moreover, electrochemical redox potentials, PL, and relative ECL-FIA studies were described for polyamine dendrimers functionalized with electrochemiluminescent polypyridyl Ru(II) complexes, synthesized through the complexation of dendritic polypyridyl hgands to Ru(II) complexes [121]. The adaptability of the newly fabricated thin-layer electrochemical flow cell for amperometric and ECL measurements combined with FI method is demonstrated. This detection is followed by spectrophotometric detection for determination of bromide using the fabricated ceU [122]. 

Caruana, D.J. and McCormack, S.P. (2002) Electrochemical redox potential in flame plasma. 

The electrochemical redox potentials are obviously not changed by the dopant as compared to the undoped electrolyte. 

Figure 6. Hole injection efficiency figure of merit for substrate contacts of varying work function vs. energy step across the contact polymer interface estimated from published work function data and electrochemical redox potential data. The height of each bar reflects the variability in injection efficiency due primarily to variation in substrate surface pretreatment and for the particular case of Au, diffusion to the interface of metal atoms from underlying binder layers.

By consideration of their electrochemical redox potentials, which permits determination of which carrier is likely to reduce another, and which is likely to be reduced. There is a gradual fall in redox potential between the enzyme that oxidizes NADH and that which reduces oxygen to water. 

The determination of electrochemical redox potentials requires standard reference compounds whose potential, ideally, does not vary. The redox couple [FeCp " (q -C6Me6)2] has a redox potential E° = -1.85 V vs. SCE that is independent on the nature of the solvent and electrolytes, because solvent molecules and electrolyte ions cannot reach the iron center due to the steric bulk of the ring methyl groups. This provides an excellent reference system, much better than ferrocene, the lUPAC reference, because these interactions can occur between the two ferrocene rings provoking variations of the potential from one solvent to the... 

Electrochemical redox potentials of aromatic hydrocarbons in aprotic solvents can be correlated to such parameters as electron affinities, u.v. absorption frequencies as well as energy levels calculated from molecular orbital theory. ... 

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