Linearly extended tetrathiafulvalene analogues with dithienyl and difuryl polyenes pi-conjugated spacers

The synthesis of new classes of extended hybrid tetrathiafulvalene analogues built around difuryl and dithienyl polyenic pi-conjugated spacers containing n = 1, 2, or 3 conjugated double bonds and bearing CO(2)Me, SMe, and n-propyl substituents (R) at the 1,3-dithiole ring is described. The electronic absorption spectra of these compounds show that the wavelength of the absorption maximum and the HOMO-LUMO energy gap depend on the nature of the heterocycle, the length of the pi-conjugated spacer and the electronic effects of R. Cyclic voltammetry shows that except for n = 1 and R = CO(2)Me, all compounds are directly oxidized into their dicationic state through a single-step two-electron transfer. The combined effects of the various structural parameters allow oxidation potentials lying among the lowest reported to date for TTF analogues to be reached.