Polypyrrole ruthenium complex

Nitration of the surface of polypyrrole and the subsequent reduction of the nitrate groups has been reported [244] and Bidan et al. [306, 307] have investigated the electrochemistry of a number of polymers based on pyrroles with /V-substituents which are themselves electrochemically active. Polypyrrole has also been successfully deposited onto polymeric films of ruthenium complexes [387], and has been used as an electrode for the deposition and stripping of mercury [388], As with most conducting polymers, several papers have also appeared on the use of polypyrrole in battery systems (e.g. [327, 389] and Ref. therein). 

Furthermore, the utilization of preformed films of polypyrrole functionalized by suitable monomeric ruthenium complexes allows the circumvention of problems due to the moderate stability of these complexes to aerial oxidation when free in solution. A similar CO/HCOO-selectivity with regards to the substitution of the V-pyrrole-bpy ligand by an electron-with-drawing group is retained in those composite materials.98 The related osmium-based redox-active polymer [Os°(bpy)(CO)2] was prepared, and is also an excellent electrocatalyst for the reduction of C02 in aqueous media.99 However, the selectivity toward CO vs. HCOO- production is lower. 

The attachment of a redox center to a calkarene-substituted PPy has been achieved by the anodic oxidation of pyrrole-substituted trisbipyridylruthenium(II)-Iinked calixarenes [307]. However, only thin films with a low amount of immobilized [Ru(bpy)3] (bpy = 2,2 -bipyridine) were obtained by homopolymerization. Thicker films could be grown from copolymerization with iV-methylpyrrole. Even if the sensory properties of these polymers have not been investigated yet, it can be predicted that the electrochemical and/or luminescent responses of the ruthenium complex could be changed upon the complexation of a guest cation by the immobilized host calixarene. It must be pointed out that such a recognition event had been already observed with a polypyrrole film N-substituted by an aza crown ether-linked bipyridine ruthenimn (II) complex [271]. 

A group in Switzerland has developed a photovoltaic cell that can function as a window for a building.376 In one example, a ruthenium pyridine complex photosensitizer is attached to the titanium dioxide semiconductor by a phos-phonate. An iodine-based electrolyte (Kl3 dissolved in 50 50 ethylene carbonate/propylene carbonate) is between the panes. All the films are so thin that they are transparent. The efficiency is 10-11%. Variants on such cells have included fullerenes377 and polypyrrole.378 The use of solid electrolytes will avoid problems that might occur if a seal on a liquid electrolyte leaked. 

H. Laguitton-Pasquier, A. Martre and A. Deronzier, Photophysical properties of soluble polypyrrole-polypyridyl-ruthenium(II) complexes, J. Phys. Chem. B, 105, 4801-4809 (2001). 

In the latter example and others involving polypyrrole films electroformed from a complex between a transition metal (Ru(II)) and a bi- or terpyridine-substituted pyrrole [201, 202], the electron self-exchange was ensured by either the viologen or Ru(II) units and not by the polymer. As a matter of fact, the PPy matrix was undoped when poly(3) was used for electrocatalytic reduction experiments or overoxidized when the films containing ruthenium(II)-based complexes were involved in oxidation experiments [201, 202]. 

As a matter of fact, the N-substitution induced in the polymer backbone a much weaker configurational flexibility than the 3-substitution. To circumvent this problem, Moutet et al. have synthesized polypyrroles N-substituted by ferrocene crown ether [270] and aza crown ether-linked bipyridine ruthenium (II) complexes [271]. Poly(19) was found to be Ba + and Ca " "-responsive [270], whereas the ruthenium(II)-based PPy was more sensitive to alkali metal cations [271]. The recognition of the cation binding was based on the changes in the electrochemical response of the metallic center instead of PPy. 

Cosnier S, Deronzier A, Roland JF (1990) Polypyridinyl complexes of ruthenium(ll) having 4,4 -dicaiboxyester-2,2 -bipyridine ligands attached covalently to polypyrrole films. J Electroanal Chem 285 133-147... 

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