Polypyrroles electronic properties

Following the discovery of the unique electronic properties of polypyrrole, numerous polymers of pyrrole have been crafted. A copolymer of pyrrole and pyrrole-3-carboxylic acid is used in a glucose biosensor, and a copolymer of pyrrole and A-methylpyrrole operates as a redox switching device. Self-doping, low-band gap, and photorefractive pyrrole polymers have been synthesized, and some examples are illustrated [1,5]. 

Polypyrrole is one of a series of heterocyclic polymers which has attracted much attention due to its characteristic electric and electronic properties. However, there are some problems relating to the physical and material properties associated with its structure. The fundamental structural formulae shown in Fig. 16.5 have been generally proposed for the structures of dedoped and doped polypyrroles, where the aromatic form corresponds to the dedoped state and the quinoid form corresponds to the doped state [9-11]. However, the actual structure appears to be more complicated. At present the exact structure is not known because the polymer is amorphous and insoluble. Consequently, various structures have been proposed for polypyrrole [10]. 

The unique electronic properties of polypyrroles and the mechanism of their conductivity have been the object of many theoretical studies <94MI 204-l0>. The future technical applications for conducting PPy polymers seems bright indeed <94MI 204-11>. 

Bolto, B.A., Mcneill, R., Weiss, D., 1963. Electronic conduction in polymers. 111. Electronic properties of polypyrrole. Aust.J. Chem. 16,1090-1103. 

B. Bolto, R. McNeill, D. Weiss, Electronic Conduction in Polymers. III. Electronic Properties of Polypyrrole. Aust. J. Chem. 1963,16,1090. 

Bredas, J.L., G.B. Street, B. Themans, and J.M. Andre. 1985. Organic polymers based on aromatic rings (polyparaphenylene, polypyrrole, polythiophene) Evolution of the electronic properties as a function of the torsion angle between adjacent rings. J Chem Phys 83 1323-1329. 

Polypyrroles are a class of conjugated polymers that have been extensively studied due to their low oxidation potential leading to stable conductors, along with the compatibility of their electroactivity in aqueous media. Since the first report on the electrochemical preparation of conductive polypyrrole films [84—87], interest in the electronic properties of this polymer and its derivatives has increasingly grown. 

As illustrated previously, PT derivatives have been the focus of much research due to their unique combination of electronic properties that include electrical conductivity, electrochromism, and structural versatility. These PTs typically have a moderate bandgap, which is in the middle of the visible spectrum while others such as polyaniHnes and polypyrroles have higher bandgaps. This gives the PTs a colored appearance (most normally red) in the neutral state and they tend to become more absorbing and opaque upon oxidation (Table 20.4). 

Chromatic changes caused by electrochemical processes were originally described in the literature in 1876 for the product of the anodic deposition of aniline [271]. However, the electrochromism was defined as an electrochemically induced phenomenon in 1969, when Deb observed its occurrence in films of some transition metal oxides [272]. Electrochromism in polypyrrole was first reported by Diaz et al. in 1981 [273]. Electrochromism is defined as the persistent change of optical properties of a material induced by reversible redox processes. Electronic conducting polymers have been known and studied as electrochromic materials since the initial systematic studies of their electronic properties. 

Aromatic heterocyclic polymers such as polypyrrole and polythiophene have low ionization potentials and low electron affinities [1, 2]. An early theoretical study on the electronic properties of these polymers indicated that electron affinity is mainly affected by substitution on the heteroatom whereas ionization potential is mainly affected by substitution on the backbone [9], Later theoretical studies on polythiophene indicated that chemical transformation of thienyl sulfur to the corresponding thienyl-5-oxide or thienyl-5,5-dioxide would deeply affect the electronic properties of the polymer as a result of the increase in both electron affinity (EA) and ionization potential (IP) [10, 11],... 

Inganas O, Lundstrom I. Electronic-properties of metal polypyrrole junctions. Synth Met 1984 10(1) 5-12. 

As part of an overall study of the electrode/electrolyte interphase of the electronically conducting polymer, polypyrrole, the surface structure and electronic properties have been investigated. 

In essence, the objective here is the ability to control the electronic properties of polypyrrole by copolymerization, rather than with choice of dopant. Copolymerizations of pyrrole with its A -methyl, A/-phenyl, N-(/ -bromophenyl) and A/-(/ -nitrophenyl) derivatives, and /V-methylpyrrole-1-acetate are described below. 

Bolto BA, McNeil R, Weiss DE (1963) Electronic conductions in polymers III electronic properties of polypyrrole. Aust J Chem 16 1090-1103... 

More recently, the discovery, development, and widespread use of conjugated polymers have made the process of electrodeposition by anodic polarization more popular because of their unique electronic properties. Indeed, conductive polymers based on aromatic compounds such as polyaniline (PANI), polypyrrole (PPy), polythiophene (PThi), poly(p-phenylene vinylene) (PPV), and their derivatives can be very easily prepared by electro-oxidation of the parent aromatic monomer [1] as illustrated by the mechanism shown in Figure 10.1. These polymers, characterized by a conjugated jt-electron system, are very rigid and exhibit strong intermolecular interactions that generally lead to insolubility either in organic solvents or in... 

We began our template synthesis work in 1985 by electrochemically synthesizing the electronically conductive polymer polypyrrole within the pores of a nanoporous polycarbonate filtration membrane [10]. Since then, we [9,11-16] and others [26-35] have explored, in some detail, the electrochemical, electronic, and optical properties of template-synthesized conductive polymers. I review this work in this chapter. Topics discussed include the membranes used to do template synthesis, the electronic properties of template-synthesized conductive polymer fibrils and tubules, and the morphology of the template-synthesized conductive polymers. 

Y. F. Nicolau and M. Nechtschein, Layer-by-layer thin film deposition of polypyrrole and polyaniline, in Electronic Properties of Conjugated Polymers, Vol. 3 (H. Kuzmany, M. Mehring, and S. Roth, eds), Springer Ser. Solid-State Sci. 91, Springer, New York, 1989 461. 

J. Lei, Z. Cai, and C. R. Martin, Effect of reagent concentrations used to synthesize polypyrrole on the chemical characteristics and optical and electronic properties of the resulting polymer, Svnth. Mel. 46 53 (1992). 

---