Polymer pendant viologen

The photoreduction of polymer pendant viologen by 2-propanol was reported to proceed by the successive two-electron transfer processes between the adjacent viologen units and the propanol which is a two-electron reducing agent44). Preferential formation of a dimeric cation radical of viologen observed was ascribed to the polymeric structure and the two-electron process. These fundamental studies on polymeric electron mediators contribute to the construction of solar energy conversion systems. 

Polystyrene pendant viologen (19) was prepared in order to use it as a polymeric electron mediator42a). The polymer itself can stabilize Pt colloids. The combined... 

In the same study, redox polymers (223) were prepared that contained pendant viologens (Scheme 108). An active reducing agent was obtained by chemical reduction with dithionite or zinc, electrochemically, or by exposure to light. Utilization of the reduced poly(viologen) (224) as an electron transfer mediator was demonstrated by addition of a catalytic amount of the polymer to a mixture of zinc powder, ethyl benzoylformate (225) and water-acetonitrile (1 5). A quantitative yield of ethyl mandelate (226) was obtained after two days at room temperature (Scheme 109). Without the polymer, no reaction was observed after a month. 

Another rather special strategy to obtain electrochromic polymers with unexpected performance is covalently connecting electrochromic units to the conjugated polymer backbone. Lee and coworkers have reported a new polymer 119 (Fig. 2.7B) thatis aPEDOT derivative containing a pendant viologen (Ko et al, 2004). Electrochemical and spec-troelectrochemical studies showed that this polymer had four colored oxidation states. 

Electrochemical oxidation of X produces a polymer film with polythiophene as the backbone and viologen centers as pendant redox groups. The electrochemical properties of the polymer are the combination of polythiophene and viologen. Using viologen subunits as the internal standard (one per repeat unit of the polymer), the "doping level" of the oxidized polythiophene backbone at its maximum conductivity can be measured and is about 25%. The charge transport via the pendant V2+/+ of poly(l) has been studied by... 

Quenching of the excited state of poly(acrylic acid-co vinylbipyridine)-pendant [Ru(bpy)3]2 + 19) by methyl viologen in alkaline aqueous medium has been studied and the effect of the polymer has been discussed 99). Among the three different molecular weight samples used (MW 2100, 4400, 13 300), the quenching of the lowest molecular weight polymer is explained to occur through a dynamic process, while the... 

Examples of electrochromic polymers bearing perfluoro chains (poly(54)) [147], dendrons (poly(170)), or viologen groups, e.g., (poly(171)) [150] have been reported. In this later case, introduction of a second electrochromic viologen pendant group increases the contrast between the oxidized and the neutral states. 

Based on this approach, polymers presenting successively different colors on oxidation have been described, e.g., polymer 172 [294,295]. Other electrochromes incorporating electroactive entities as pendant group, such as viologen in 173, leads to the observation of two optical states on oxidation [296]. 

Other functionalities that have been added to thiophenes include redox-active pendant groups such as anthraquinone and viologen [70,71]. These polymers offer the ability to reach multiple colored states due to the electrochromism of both the thiophene polymer and the pendant group combined. 

Polythiophenes, 3-substituted by bipyridyl [268], benzoquinone [269], viologen [270], ferrocene [271], and tetrathiafulvalene [272], have been reported. The redox group is generally apparent in the voltammetric response of the polymers obtained, while the response of the polyconjugated chain is not, an indication of degradation of the backbone. Polymers of better quality with ferrocene and viologen pendants were later electrodeposited from bi- and terthiophenes [273]. 

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