2-(Thiopyran-4′-yliden)-1,3-dithioles fused with thiophene units: intramolecular S ⋯ S interaction affecting the redox properties and molecular geometries

The title molecules (1) are strong electron donors like tetrathiafulvalene (TTF) but possess non-planar geometries with short intramolecular contacts between S atoms (av. 3.06 Å in 1b, X-ray); by contrast, their cation radicals are endowed with molecular planarity, and the shorter S ⋯ S contacts (av. 2.87 Å in 1b˙+, X-ray) result in the enhanced attractive interaction as well as much smaller Coulombic repulsion in 12+ than in TTF2+.