| Abstract
| - Thin films of tetrahexylsexithiophenes, fluorenonyl- and fluorenyl-protected at the terminal α,ω-positions, were investigated by cyclic voltammetry, electrochemical quartz crystal microbalance analysis,in situ ESR, and in situ conductivity. Reversible oxidation is composed of three separate steps, twoone-electron processes and a further multielectron process. ESR indicates strong magnetic dimerizationfor the one-electron-oxidized species. Conductivity is redox type at the cation−dication (polaron−bipolaron) state and metal-like at doping levels higher than the bipolaron with a 20-fold increase at fulloxidation. Hexyl-substituted α,ω-capped octathiophene, decathiophene, and dodecathiophene films havebeen similarly investigated to compare the effects of fluorenonyl and fluorenyl extension of sexithiophenewith those given by additional thiophene rings. The conductivity, which increases progressively (by 3orders of magnitude) with the oligothiophene chain length, is metal-like. In dodecathiophene the dopingcharge increases markedly, approaching four electrons per molecule, and the conductivity, maximized atthe two-electron level, decreases linearly, approaching zero at the four-electron level. A bipolaron modelof conductivity accounts for conductivity in oligothiophenes.
- Thin films of α,ω-fluorenonyl- and fluorenylsexithiophenes and α,ω-capped octa-, deca-, and dodecathiophene are investigated by CV, electrochemical quartz crystal microbalance analysis, in situ ESR, and in situ conductivity. Reversible oxidation of sexithiophenes occurs in two one-electron steps with redox conductivity followed by a multielectron process bearing metal-like conductivity. Longer oligothiophenes are oxidized in a single redox process with metal-like conductivity.
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