Conjugated polymers self-doping

Shortly after discovery of methods for preparation of organic soluble derivatives of poly(phenylene vinylene) and polythiophene, Wudl and coworkers reported preparation of each of these polymers with sulfonated side groups. The specific objective of this work was based on the idea that the anionic sulfonate groups could make the polymers self-doping , wherein the covalently linked anionic units could serve to provide charge compensation when the polymer backbone is in the oxidized (semiconducting) state. These first studies focused on the synthetic monomer and polymer chemistry. However, the authors reported in their papers that their newly synthesized conjugated... 

In a recent pubHcation, Alivisatos and co-workers reported the making of hybrid nanorods-polymer solar cells and their properties [122]. These solar cells were made by spin casting of a solution of both poly(3-hexylthiophene) (hole acceptor) and CdSe nanorods (electron acceptor) onto indium tin oxide glass substrates coated with poly(ethylene dioxythiophene) doped with polystyrene sulfonic acid and aluminum as a top contact. Nanorods have been used in composites so as to improve the carrier mobiHty. Indeed, the latter can be high for some inorganic semiconductors, but it is typically extremely low for conjugated polymers [123]. The use of the nanorods suppHes an interface for the charge transfer as well as a direct path for electrical transport. Also, because of their anisotropy, self-assembly of these nanorods is observed by electron microscopy. It shows... 

The cyclopolymerization of dipropargyl monomers carrying an ionic nature is a facile synthesis method for self-doped conjugated ionic polymers. Various dipropargyl quarternary ammonium salts were polymerized to yield the unusual conjugated polymers. The potential counterions are ionically bound to the... 

The conductivity of polymer is observed to be around 3.6x10 S/cm. These conductivity values of both the polymers (Figure 5.44 and 5.45) are reported to be higher than pyridine based conjugated polymers due to self-doping properties. 

Y. S. Gal, S. H. Jin, A self-doped ionic conjugated polymer poly(2-ethynyl-pyridinium-N-benzoylsulfonate) by the activated polymerization of 2-ethynylpyridine with ring-opening of 2-sulfobenzoic acid cyclic anhydride, Bulletin of the Korean Chemical Society 2004, 25, 777. 

Y. S. Gal, S. H.Jin, K. T. Lim, S. H. Kim, K. Koh, Synthesis and electro-optical properties of self-doped ionic conjugated polymers poly 2-ethynyl-N-(4-sulfobutyl)pyridinium betaine, Current Applied Physics 2005, 5, 38. 

Scheme 2. A possible precursor route to a self doping conjugated polymer.

In addition to positively impacting issues of dedoping of pH and thermally sensitive polymers such as polyaniline, self-doped forms enable the combination of p- and n-type conducting polymers without their spontaneous discharging by the concerted recombination of carriers and counterions. This has resulted in the formation of conjugated polymer p/n junctions, not possible with standard conjugated polymers. ... 

Self-doped conducting polymers are conjugated polymers, in which at least a fraction of monomer units contain covalently attached, ionizable functional groups that can act as immobile dopants. These polymers can be synthesized in a number of ways including chemical or electrochemical modification of the parent polymer as well as chemical or electrochemical polymerization of substituted monomers to form homo- or copolymers. ... 

Other 3-substituted thiophenes that have been polymerized include 3-methoxy [309-311], other 3-alkoxy [312], 3-phenyl [313,314], 3-(4-methoxyphenyl) [314], 3-(4-trifluoromethylphenyl) [314], 3-bromo [315], 3-alkylsulfonatethiophene [316-318], and others [319-323]. Poly-3-alkylsulfonate thiophenes are particularly interesting due to a striking property. Sodium poly-3-thiophene-j8-ethanesulfonate and sodium poly-3-thiophene-6-butanesulfonate and their conjugate acids are water soluble in both the doped and undoped states [317,318]. Ikenoue et al. [318] examined the conduction mechanism for this self-doped conducting polymer. 

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