Linearly extended hybrid tetrathiafulvalene analogues with bridged dithienylethylene pi-conjugating spacers

New linearly extended pi-electron donors based on bridged dithienylethylene (DTE) end-capped with diversely substituted 1,3-dithiol-2-ylidene electron-releasing groups have been synthesized by Wittig-Horner olefination of appropriate aldehydes. Cyclic voltammetry shows that whereas the unbridged analogues are directly oxidized to the dication state through a two-electron transfer, rigidification of the DTE spacer leads to the splitting of the two-electron wave into two successive one-electron steps due to the decrease of the potential corresponding to the formation of the cation radical. This unusual electrochemical behaviour is interpreted with the help of theoretical calculations which suggest that these effects are related to the enhanced electron delocalization resulting from the rigidification of the DTE spacer. This conclusion is supported by an X-ray diffraction structural analysis which reveals that in addition to a fully planar conformation stabilized by intramolecular S ... S interactions, the bridging of the DTE spacer leads to a significant reduction of bond length alternation.