Methyl viologen

Ramsden J J and Gratzel M 1986 Formation and deoay of methyl viologen radioal oation dimers on the surfaoe of oolloidal CdS Chem. Phys. Lett. 132 269-72... 

The divalent cation methyl viologen is highly colored in reduced form and is used as an electrochromic in solution cells (Eig. 11). 

In related work, palladium, nickel, or methyl viologen (MV ) were used to catalyze the conversion of perfluoroalkyl iodides to a-perfluoroalkyl carbinols in the presence of zinc [43, 44] (equations 32 and 33) Only aldehydes react under these conditions... 

Although Ru(bipy)2+ alone will not split water into hydrogen and oxygen, it has been accomplished with Ru(bipy)2+ using various catalysts or radical carriers. Perhaps the most studied system for the photoreduction of water involves using methyl viologen as the quencher, EDTA as an electron donor (decomposed in the reaction) and colloidal platinum as a redox catalyst (Figure 1.19). 

Membrane, 141, 178 Mercury electrodes, 62, 108 Mercury film electrode, 76, 110 Metals, 75, 81 Metal complexes, 64 Methyl viologen, 43 Michaelis-Menten kinetics, 175 Microbalance, 52, 53 Microcells, 102 Microchip, 194, 195... 

With ft2 and ft3 known, k could thus be determined. In a related example, a number of reactions of alkyl radicals (CH, C2H, etc.) have been studied by the application of similar principles. An intensely colored probe that reacts with R was added with (or without) the substrate of interest. The probe is a species like the methyl viologen radical ion, MV,+. If S represents the substrate, the scheme is... 

The amount of antibody immobilized on the sensor chip decreased with increasing concentration of methyl viologen. To enlarge the difference in the sig-... 

MV /MV " (HV is heptyl viologen and MV is methyl viologen). The specific effects of iodide on the electrochemical behavior of the layer-type compounds were compared, and the characteristics of several PEC cells were described. The interface energies for n-MoSe2 in contact with various redox couples were given as in Fig. 5.9. 

Ward MD, White JR, Bard AJ (1983) Electrochemical investigation of the energetics of particulate titanium dioxide photocatalysts. The methyl viologen-acetate system. J Am Chem Soc 105 27-31... 

Organic Molecules It can be seen from our earlier discussion that the presence of a transition metal ion is not always required for an electrochromic effect. Indeed, many organic molecules can yield colored products as a result of reversible reduction or oxidation. 4,4 -Bipyridinium salts are the best known example of such compounds. These compounds can be prepared, stored, and purchased in colorless dicationic form (bipm +). One electron reduction of the dication leads to the intensely colored radical cation (bipm+ ). Such radical cations exist in equilibrium with their dimers (bipm ). In the case of methyl viologen, the radical cation is blue and the dimer is red. By varying the substient group in the molecule, different colors can be obtained. 

Methyl viologen (l,T-dimethyl-4,4 -bipyridylium dichloride, MV " ) promotes photoanodic dissolution in aerated CdS solution Figure 8 shows how the rate of dissolution depends on the concentration. The colloid has a weak fluorescence at 620 nm which is quenched by. The curves for fluorescence and dissolution in Fig. 8 are symmetric, which indicates that the two processes have a common intermediate that reacts with M. These effects are explained by the following mechanism ... 

Fig. 8. Intensity of fluorescence and rate of photoanodic dissolution of colloidal CdS as function of the concentration of added methyl viologen...

Photoanodic dissolution in the presence of air and its promotion by methyl viologen was also observed for alkaline solutions of colloidal cadmium phosphide, CdjPj and cadmium arsenide, CdjAsj Bismuth sulfide, Sb Sj, photo-dissolves in the presence of air mainly according to... 

The metal formed is deposited on the colloidal particles and causes the absorption of the solution to increase at all wavelengtlK. The depositel cadmium is very reactive. It is reoxidized when air is admitted to the illuminated solution. Addition of methyl viologen to the illuminated solution under the exclusion of air yields the blue colour of the semi-ceduced methyl viologen, MV". As the absorption coefficient of MV" is known, the concentration of reduced cadmium can be readily calculated. reoxidises cadmium atoms ... 

Gratzel and co-workers found in their first flash experiments that the luminescence of CdS decayed with a lifetime of 0.3 ns When methyl viologen was present, the signal of the half-reduced electron acceptor, MV, was present immediately after the laser flash. With increasing concentration, the amount of MV formed... 

Nosaka and Fox determined the quantum yield for the reduction of methyl viologen adsorbed on colloidal CdS particles as a function of incident light intensity. Electron transfer from CdS to MV " competes with electron-hole recombination. They derived a bimolecular rate constant of 9 10 cm s for the latter process. 

Serpone et al. studied the fluorescence emitted from a CdS sol containing half-reduced methyl viologen, MV, and residual the MV being produced by... 

In the pulse radiolysis studies on the reaction of MV with TiOj, the sol contained propanol-2 or formate and methyl viologen, MV Ionizing radiation produces reducing organic radicals, i.e. (CH3)2COH or C02 , respectively, and these radicals react rapidly with MV to form MV. The reaction of MV with the colloidal particles was then followed by recording the 600 nm absorption of MV . The rate of reaction was found to be slower than predicted for a diffusion controlled reaction. 

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