β-Functionalised α,α’-conjugated oligothiophenes with alkylsulfanyl groups: synthesis and characterisation

α-Oligothiophenes are important materials for optical and electronic devices and are used as model compounds for the characterisation of charge carriers in conjugated chains. The presence of substituents in β- position of the thiophene ring improves solubility and processability and enables the chemical-physical properties of these materials to be modulate. Among the substituents, the choice of alkylsulfanyl groups is due to the electron donor effect of the sulfur atom which positively reduces the band-gap between ground and excited state, and influences the electrical and optical properties interesting in relation to possible applications of these materials. A synthesis of a homologous series of β-substituted oligothiophenes bearing alkylsulfanyl groups up to octatiophenes is discussed. The alkyl residues of the alkylsulfanyl moieties are methyl-, butyl-, octyl- and (+)-(S)-2-methylbutyl groups. The regiochemistry of all synthesised oligomers is unambiguously assessed by using 1H and 13C NMR spectroscopy. The electrochemical behaviour of some of these derivatives is analysed in relation to their potential applicability in electrochemical devices.