Conductive thiophene oligomers

Redox molecules are particularly interesting for an electrochemical approach, because they offer addressable (functional) energy states in an electrochemically accessible potential window, which can be tuned upon polarization between oxidized and reduced states. The difference in the junction conductance of the oxidized and the reduced forms of redox molecules may span several orders of magnitude. Examples of functional molecules used in these studies include porphyrins [31,153], viologens [33, 34,110,114,154,155], aniline and thiophene oligomers [113, 146, 156, 157], metal-organic terpyridine complexes [46, 158-163], carotenes [164], nitro derivatives of OPE (OPV) [165, 166], ferrocene [150, 167, 168], perylene tetracarboxylic bisimide [141, 169, 170], tetrathia-fulvalenes [155], fullerene derivatives [171], redox-active proteins [109, 172-174], and hydroxyquinones [175]. 

Much work has been directed towards the synthesis of thiophene oligomers and polymers. This is due to the current interest in research on conducting polymers and molecular electronics (92CRV711). Two main approaches have been used for making such polymers (i) chemical (e.g. FeCl3) or electrochemical oxidation of monomeric thiophenes and (ii) transition metal-catalyzed cross-coupling reactions. 

The conditions for polymerization were also foimd to be crucial in relation to polythiophene and polybithiophene films [58,80,84,114-121], The relatively high potential required for the oxidation prevents the use of many metallic substrates. The electrochemical oxidation of substituted thiophenes and thiophene oligomers yields conducting polymers, and these compounds can be electropolymerized at less positive potentials, so it is a good strategy to use these derivatives instead of thiophene (see Sect. 2.2.6). Another approach is the deposition of a thin polypyrrole layer that ensures the deposition of polythiophene on these substrates (eg., Ti, Au) [115]. Interestingly, other polymers as well as copolymers and composites (see Chap. 2) can also be synthesized. 

Thiophene oligomers (dimer and trimer) separated by an insulating CH2-CH2 bridge (13) were electropolymerized [146]. In the latter case the product, resulting from dimerization, displays a lower conductivity than... 

In situ UV-vis spectroscopy of PT reported by Onoda et al. [924] revealed the polaron state at 0.4 eV above the valence band and at 0.4 eV below the conduction band with an overall bandgap of 2.1 eV [925]. Interpretation and assigment of UV-vis spectroscopic data can be supported by investigations of model compounds reported by Fichou et al. [926]. Their results obtained with thiophene oligomers strongly support the preceeding band... 

Sauvajol JL, Lere-Porte JP, Moreau JJE (1997) Silicon-containing thiophene oligomers and polymers synthesis, characterization and properties. In Nalwa NS (ed) Conductive polymers. Handbook of organic conductive molecules and polymers, vol 2. Wiley, New York... 

J. V. Caspar, V. Ramamurthy and D. R. Corbin, Preparation and spectroscopic characterization of polarons and bipolarons of thiophene oligomers within the channels of pentazil zeolithes the evolution of organic radical ions into conducting polymers, J. Am. Chem. Soc., 1991, 113, 600. 

G. Zotti, S. Zecchin, G. Schiavon, and L. Groenendaal. 2002. Electrochemical and chemical synthesis and characterization of sulfonated poly(3,4-ethylenedioxy-thiophene) A novel water-soluble and highly conductive conjugated oligomer. Macromol Chem Phys 203(13) 1958-1964. 

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