Syntheses and crystal structures of fused thiophenes: [7]helicene and double helicene, a D2-symmetric dimer of 3,3'-bis(dithieno[2,3-b:3',2'-d]thiophene).

The efficient synthesis of (TMS)(2)-[7]helicene (rac-3) and double helicene, a D(2)-symmetric dimer of 3,3'-bis(dithieno[2,3-b:3',2'-d]thiophene) (rac-4) was developed. The crystal structures of 3 and 4 show both strong intermolecular pi-pi interactions and S...S interactions. UV/vis spectra reveal that both 3 and 4 show significant pi-electron delocalization.