EXTREMELY EXPANDED TETRATHIAFULVALENES WI TH POLYENE SPACERS - CAROTINOID TETRATHIAFULVALENES - POLYMETHIN-TETRACYANOTETRATHIAFULVALENE RADICAL CATIONS, A NEW CLASS OF VIOLENEN

The synthesis of extended tetrathiafulvalenes 11 with di-, tetra-, hex a-, octa-, deca- and dodecamethine spacers is described by a PPh(3)-in duced Wittig-reaction-like condensation of the corresponding polyenedi als 10 with 2-thio-1,3-dithiole-4,5-dicarbonitrile (9). By the same pr ocedure, the dimethyloctamethine- and the tetramethylhexadecamethine-t etrathiafulvalenes 14 and 15, respectively, were obtained. The extende d tetrathiafulvalenes represent multistep vinylogous redox systems of the 'violene type'. They can be oxidized to give the cyanine-like radi cal cations, e.g. 11(sem), 14(sem), and 15(sem), and the dications, e. g. 11(ox), 14(ox), and 15(ox); their UV/VIS/NIR spectra are reported. The crystal and molecular structure of 1,8-diylidene)bis[1,3-dithiole- 4,5-dicarbonitrile] (11e) was determined: it is a rod-like, planar mol ecule; in the crystal, it forms staples along the longest molecule axi s. The CV measurements confirm that the redox potentials of 11, 14, an d 15 decrease asymptotically with the increasing length of the spacer. Because of the close relationship of the extended tetrathiafulvalenes (ETTF's) to the carotinoids, they are named 'caroviologenes'; they fo rmally belong to the class of molecular wires.