Synthesis and electron-donor ability of the first conjugated pi-extended tetrathiafulvalene dimers

A series of novel conjugated homo (16a,b) and heterodimers (20) of pi-extended tetrathiafulvalenes with p-quinodimethane structures (exTTFs) linked by a conjugative vinyl spacer have been prepared by olefination Wittig-Horner reaction from the corresponding quinones (14, 19) and phosphonates (15a,b). The redox properties, determined by cyclic voltammetry, reveal a strong donor character and the presence of only one four-electron oxidation wave to form the tetracation species at oxidation potential values quite similar to those found for the related monomers. Theoretical calculations (PM3) show a planar central stilbene moiety and highly distorted exTTF units. The electronic spectra support as well as the electrochemical data and theoretical calculation the lack of significant communication between the exTTF units.