Polythiophenes bandgaps

Related Polymer Systems and Synthetic Methods. Figure 12A shows a hypothetical synthesis of poly (p-phenylene methide) (PPM) from polybenzyl by redox-induced elimination. In principle, it should be possible to accomplish this experimentally under similar chemical and electrochemical redox conditions as those used here for the related polythiophenes. The electronic properties of PPM have recently been theoretically calculated by Boudreaux et al (16), including bandgap (1.17 eV) bandwidth (0.44 eV) ionization potential (4.2 eV) electron affinity (3.03 eV) oxidation potential (-0.20 vs SCE) reduction potential (-1.37 eV vs SCE). PPM has recently been synthesized and doped to a semiconductor (24). 

Mechanically durable and structurally flexible polythiophene derivatives have been prepared that are useful as semiconducters in thin film field effect transistors and are soluble in chlorobenzene. Materials prepared from these agents have a bandgap between 1.5 and 3.0 eV that enhance their function as film transistors. 

Early progress in polythiophene chemistry was achieved by the synthesis of mono- and dialkoxy-substituted thiophene derivatives developed by Leclerc [6] and industrial scientists at Hoechst AG [7-9]. However, most polymers of mono- and dialkoxythiophenes exhibited low conductivity in the oxidized, doped state. A breakthrough in this area was the synthesis of polymers of the bicyclic 3,4-ethylenedioxythiophene (EDT or EDOT) and its derivatives—electrochemically polymerized by Heinze et al. and chemically polymerized by Jonas et al. of the Bayer Corporate Research Laboratories [10,11]. In contrast to the nonbicyclic polymers of mono- and dialkoxythiophenes, PEDT has a very stable and highly conductive cationic doped state. The low HOMO-LUMO bandgap of conductive PEDT allowed the formation of a tremendously stable, highly conductive ICP [12]. Technical use and commercialization quickly followed today ICPs based on PEDT are commercially available in multiton quantities. 

Reviews on polythiophenes, polysquarines, polybenzenes, etc. have appeared elsewhere, which also discuss the tunability of the bandgap of conjugated polymers [7]. Further sections of this chapter will focus on the synthesis and characterization of the underivatized thienothiophenes (a-c) and conjugated... 

FIGURE 12.2 Polythiophene analogs with reduced bandgaps. 

Johansson, T., W. Mammo, M. Svensson, M.R. Andersson, and O. Inganas. 2003. Electrochemical bandgaps of substituted polythiophenes. J Mater Chem 13 1316-1323. 

Since the discovery of a highly conductive polyacetylene film in 1977 [33], various conductive materials have been developed based on the polymerization of five-membered heteroaromatics represented by polythiophene (2). Polyselenophene (3) was also obtained by chemical polymerization [34-36] or electrochemical polymerization of selenophene (Scheme 6.2) [37-39]. The bandgap energy of polyselenophene... 

A comparison of the bandgaps of polythiophene and thienoacene illustrate this point. Figure 7.7 shows the frontier orbitals of the latter polymer (Tian and Kertesz, 2008). (Note that whereas several thienoacene oligomers have been synthesized and characterized the corresponding polymers have not yet been made.) If all C-C bond distances were equal, which is not the case, as will be emphasized subsequently, the difference between the HOCO orbitals in Figures 7.5 and 7.7 would be minor and the difference would be due only to the different conformations of the underlying polyacetylene-like n-orbital chain. 

Various conjugated polymers, such as poly( >-phenylene) (PPP), polythiophene (PTh) and polypyrrole (PPy), have aromatic ring units in the conjugated backbone as illustrated in Figure 7.1. The aromatic rings usually enlarge the bandgap relative to PA. The increase in the gap of e.g. PTh relative to PA can be rationalized in two alternative ways ... 

This chapter focuses on the use of polythiophene derivatives [11] as active electrode materials in electrochemical capacitors. First, the concept of electrochemical capacitors is presented in order to highlight the electrochemical properties of polythiophenes that make them suitable for this application. Second, the various wide- and narrow-bandgap derivatives of polythiophenes that have been investigated are discussed. 

A survey of the polythiophene derivatives that have been considered and tested as active electrode material in electrochemical capacitors can be roughly divided between wide- and narrow-bandgap derivatives. The structure of monomers of the corresponding polymers is presented in Schemes 15.1-15.4. 

Scheme 15.2 Structures of wide-bandgap polythiophene derivatives...

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