Synthesis and properties of the first highly conjugated tetrathiafulvalene analogues covalently attached to [60]fullerene

The synthesis of the first C-60-based donor-acceptor (D-A) systems (12a-c) in which the C-60 core is covalently linked to strong, highly conjugated pi-electron donors derived of tetrathiafulvalene (TTF) with p-quinodimethane structure has been carried out by cyclization with azomethine ylides following Prate's procedure. The synthetic strategy requires the preparation of the novel formyl-substituted pi-extended donors which, in turn, are prepared in a multistep synthetic procedure by reaction of 2-formyl-9,10-anthraquinone (6) with the appropriately substituted phosphonate esters (8). Semiempirical PM3 calculations predict a geometry highly distorted from planarity for the donor fragment and a most stable conformation in which both 1,3-dithiole rings are far away from the [60]fullerene surface. The redox properties were determined by cyclic voltammetry in solution and reveal the presence of four cathodically shifted reduction waves, relative to C-60 and corresponding to the C-60 core, and a two-electron single oxidation wave to form stable dication species of the pi-extended donor units. Magnetic susceptibility measurements clearly indicate a paramagnetic behavior in the solid state, and a remarkable conductivity is observed for these single component organic compounds.