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Encyclopedia of Nanoscience and Nanotechnology Edited by H. S. Nalwa Volume 4: Pages (113-130)

Scheme 1. For polypyrroles and polythiophenes, n is usually ca. 3-4. For optimal conductivity, there is a positive charge on every third or fourth pyrrole or thiophene unit along the polymer chain. For the conducting emeraldine salt form of polyaniline (III) a radical cation resides at alternate N sites.

ultraviolet-visible (UV-vis) spectrum for PPy containing DNA as dopant is shown in Figure 1. This UV-vis spectrum shows the typical polaron/bipolaron 475 nm bands of doped polypyrrole at ca. 500 nm and 900 nm. The exact location of these bands is dependent on the dopant used. As illustrated in Figure 2, when 8-hydroxyquinoline-5-sulfonic acid (HQS) is used as dopant, the lower wavelength peak is even further blueshifted. The dopant also influences the degree of absorption in the near infrared beyond 900 nm and this is attributed to changes in polymer conformation (tight coil versus expanded coil). The polymer conformation has been found to be substrate dependent, with polypyrroles deposited on hydrophilic glass displaying an absorption band at 1180 nm, which is replaced by a free carrier tail extending to 2600 nm for polymers deposited on hydrophobic surfaces [29].

As well as varying the functional properties of ICPs, the dopant plays a key role in determining the electronic (conductivity) and mechanical properties (e.g., tensile strength) of the resultant material. For example, even slight changes in the molecular structure [30] of a range of sulfonated aromatic dopants influence these properties (Table 1). The incorporation of surfactant-like dopants such as dodecylbenzene sulfonate has also proved useful in sol-

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