Viologen moiety

In order to verify Okuyama s prediction on molecular orientation in bilayer assemblies, azobenzene amphiphiles having a viologen moiety as a hydrophilic head group, CnAzoCmV2+ 2Br, were newly prepared. Bathochromic shift to 390 nm in the visible absorption band of the... 

Dissymmetrical SUVs can be formed by limiting reactions to the outer surfaces of polymerized surfactant vesicles (Fig. 39). Chemical dissymmetry has been created, for example, in polymerized vesicles prepared from surfactants containing ester-linked viologen moieties in their headgroups. Cleavage of the... 

Despite some small spectral differences, the similarities have been sufficient to confirm the slow step in the electrochemistry of immobilized cobalt porphyrin mediators (113) and to identify the intermediates involved in a tetrathiafulvalene polymer coated electrode (7). A polyxylylviologen -polystyrenesulfonate co-polymer coated electrode, on the other hand, showed no changes in the position of the peaks in the absorption spectra upon immobilization (111). Presumably this indicated an absence of interactions between neighboring viologen moieties. Similar spectral results have been obtained using photoacoustic spectroscopy (PAS). Heptyl viologen adsorbed on Pt exhibited an unshifted spectrum which correlated with the electrochemical results (115). 

ZnMb is carried out more efficiently by the (S,S) isomer than that by the (R,R) isomer, the stereoselectivity becomes smaller than that in the reaction by monovi-ologens the selectivity is 1.2 for R= 1-naphthyl, 1.1 for R= 1-phenyl, and 1.1 for R= 1-cyclohexyl. The smaller stereoselectivity arises because bis-viologen has only one optically active substituent on one viologen moiety and an achiral methylene group on the other moiety. 

The fluorescence properties of viologen-linked fV-alkylporphyrins and their zinc(II) complexes having a tii- or hexamethylene chain are discussed on the basis of the orientation between the viologen moiety and the porphyrin plane. The fluorescence decay of the porphyrins with a trimethylene chain in acetonitrile solutions has two components corresponding to the two conformers, closed and perpendicular ones, the latter being slower than the former. The hexamethylene-bridged dyad has one major component in the fluorescence decay. 

In this work we report the fluorescence properties of the dyad systems (1 - 4) on the basis of the orientation between the viologen moiety and the porphyrin plane. 

The viologen-linked dyads have also two components. The fast component (xi) might be a closed form, where the viologen moiety is close to the porphyrin plane the bipyridinium ring is able to wag, although the fi ce rotation around the Af-CH2 bond is restricted. The other slow... 

We reasoned that the interplay between viologen cation radical dimerization and viologen- donor interaction could be utilized to develop more sophisticated mechanisms of dendrimer assembly under redox control. Driven by this hypothesis, we prepared a new series of dendrimers, similar to 16-18, but containing a dialkoxyben-zene aromatic donor residue instead of the electron acceptor viologen moiety [60]. The new series of dendronized dialkoxybenzene derivatives (26-28) is shown below. 

Upon reduction in the region where the cation radical PTV+ was formed, a new signal with hyperfine structure, due to the reduced viologen moiety, could be seen superimposed on the previous one.26 The presence of the hyperfine structure indicated the high flexibility of the alkyl-chain-bound viologen units. 

When the metal in these systems is cobalt, the Co tiis-bipyridine and viologen moieties of Co P -V readily undergo redox reactions at similar potentials to those of the isolated systems (Co tris-bipep E° = +0.15 viologen E = -0.64, both versus saturated NaCl calomel electrode (SSCE) pH = 7.0, determined by cychc voltammetry). When the metal is ruthenium, the Ru(II) tris-bi-pyridine excited state, Ru(II ), is expected to have —0.8 V (17). 

Figure 4. Fulse radiolysis transient absorption data for Fe-Pj2-Vy illustrating the prompt reaction of CO with the viologen moieties in the maquette. Note that there is a slow (ca. 40 decay of the viologen absorption, effectively putting...

Figure 5.44 Reversible reduction and oxidation of a viologen moiety of an anion exchange membrane.

Figure 5.45 Change in absorption spectra with irradiation time of an anion exchange membrane containing a viologen moiety measured in (a) pure water and (b) 0.50 N sodium chloride solution...

Figure 5.46 Effect of pre-irradiation time on Pas°4 of an anion exchange membrane containing a viologen moiety (divinylbenzene 10%). Dotted line without photoirradiation (X) with photoirradiation. After an anion exchange membrane with viologen moiety had been irradiated for various periods (irradiated at the desalting side of the membrane 0—8h), a mixed solution of 0.02 N sodium sulfate and 0.02 N sodium chloride (concentration of sodium ions 0.04 N) was electrodialyzed with photoirradiation (desalting side) at 1.0 mA cm 2 for 60 min at 25.0 °C.

As the viologen moiety of the anion exchange membrane is reduced by photoirradiation, electrons are released from the membrane. Though the first reduction potential (MV2+ + e —> MV+ = —0.45V) cannot reduce water molecules,121 the released electron might behave like an hydrated electron in the... 

Figure 5.48 Generation of photovoltage from an anion exchange membrane having a viologen moiety by irradiation with a Xe lamp (load resistance 200 kQ). 1 First irradiation 2 second irradiation (measured 31 days after the first measurement 3 third irradiation (measured 2 h after the second measurement).

T. Sata, Y. Matsuo, T. Yamaguchi and K. Matsusaki, Preparation and transport properties of anion-exchange membranes containing viologen moieties as anion exchange groups in the presence or absence of photoirradiation, J. Chem. Soc., Faraday Trans., 1997, 93, 2553. 

T. Sata, Anion exchange membrane with viologen moiety as anion exchange groups and generation of photo-induced electrical potential from the membrane, J. Membr. Sci., 1996, 118, 121-126. 

Figure 6.45 Photovoltage generation from an anion exchange membrane having a viologen moiety with and without a Ti02 layer. Dotted line from photocell of anion exchange membrane without Ti02 layer solid line from photocell with an anatase-Ti02 layer (a porous layer of finely powdered Ti02 is on the illuminated side of the membrane).

Viologen-acrylamide copolymers have been used in a similar manner to entrap enzymes and carry out direct reduction of the active site by bound viologen moieties. In these studies the polymer was reduced chemically rather than electrochemically, but there appears no reason in principle why this same chemistry could not be carried out on an electrode. These viologen-acrylamide copolymers have been shown to reduce nitrate reductase (EC 1.9.6.l/ and glutathione reductase (EC 1.6.4.2). 2 >... 

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