Oligo(furan-2,5-diylvinylene)s as pi-conjugating spacers in linearly extended hybrid tetrathiafulvalene analogues

The synthesis of a new series of push-push systems based on furan-2,5-diylvinylene oligomers end-capped with 1,3-dithiol-2-ylidene electron-releasing groups is described. H-1 NMR spectroscopy and X-ray diffraction reveal that the molecules adopt a planar conformation stabilized by strong intramolecular interactions. Electronic absorption spectroscopy indicates that the effective conjugation length increases steadily with the length of the pi-conjugated system without any evidence of saturation. Analysis of electrochemical behaviour by cyclic voltammetry shows that, whereas all compounds are easily oxidized into stable dications, with extension of the conjugation length the oxidation process progressively evolves from two successive one-electron steps to a single step two-electron transfer.