Alkylthio-substituted oligothiophenes: The influence of the alkyl chain length on the solid-state and solution properties of 4,4'-bis(butylthio)-2,2'-bithiophene

A solid-state (single crystal X-ray, IR, DSC) and solution (H-1 NMR nuclear Overhauser effect (NOE) and longitudinal relaxation times (T-1)) study of 4,4'-bis(butylthio)-2,2'-bithiophene is reported. The two thienyl rings are coplanar and in an anti orientation in the solid state, whereas a low amount of syn form is present in solution. The n-butylthio chain adopts a fully extended, nearly idealized, anti conformation in the crystal, with all the non-H atoms of the whole molecule strictly coplanar, despite the molecular length, but does not show a preferred orientation in solution. The observed changes on passing from the solid to the solution state are indications of the potential solvatochromic and thermochromic properties of beta-butylthio-substituted oligomers and polymers.