Fluoroalkylsilane (FTS) acts as an efficient p-type dopant for organic semiconductors. FTS-doped films of the semicrystalline PBTTT polymer exhibit relatively high conductivities. We demonstrate that highly doped PBTTT films exhibit a metallic nature with clear Pauli paramagnetism as observed microscopically using electron spin resonance spectroscopy. The metallic state is realized within crystalline grains, as confirmed from the anisotropy of the ESR signal.

Microscopic signature of metallic state in semicrystalline conjugated polymers doped with fluoroalkylsilane molecules.

Publisher Summary This chapter discusses the spectroelectrochemistry of conducting polymers. The intrinsically conducting polymers (ICPs) can be prepared from a large number of organic monomers by chemical or electrochemical methods. Both approaches involve the oxidation of the educt by using either appropriate oxidants or the anode in an electrochemical cell. Except for polyacetylene, all monomers and their respective polymeric oxidation products contain heteroatoms like oxygen, nitrogen, and sulfur. Those monomers, which can be electropolymerized, always contain heteroatoms. Polyaniline (PANI) is an outstanding member of the family of intrinsically conducting polymers. This family represents a fairly new class of materials that combine typical properties of metals and synthetic polymers. PANI and the polymers of substituted anilines can be formed by chemical oxidation or electrooxidation. Although the former process is more suitable for the production of large volumes of polymers, it results predominantly in powders that are difficult to process. A simple way to distinguish between a metallic conductor and a semiconductor is to measure the electronic conductivity of the substance under investigation as a function of temperature. This was attempted with PANI ex situ . Although protonation and deprotonation are no electrochemical processes, spectroscopic evidence obtained in investigations of these processes are considered because of the central importance of protonation for the occurrence of electronic conductivity in PANI.

Spectroelectrochemistry of conducting polymers

The influence of the PANI structure on the conductive mechanism and on the electrical equivalent circuit analysis

: While undoped polymers are insulators, doped conducting polymers have conductivities comparable to conventional metals and semiconductors despite their polymer chain structure. Models for the doping induced insulator-metal transition and the metallic conductivity of conducting polymers are introduced. The electrical charge transport data including DC conductivity, magnetoresistance, thermoelectric power, and microwave and optical dielectric constant of a wide range of conducting polymer materials are reviewed. A summary of the structural order and the density of states at the Fermi level of conducting polymers is also presented. The metallic properties of conducting polymers are a function of the structural order of the polymers.

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T. Obana

Papers

In situ ESR of polyaniline by electrochemical doping ; polaron to Pauli-like instead of polaron to bipolaron