Planar beta-linked oligothiophenes based on thieno[3,2-b]thiophene and dithieno[3,2-b:2',3'-d]thiophene fused units

A series of planar beta-linked oligothiophenes based on thieno3,2-b]thiophene and dithieno3,2-b:2',3'-d]thiophene fused units were synthesized. The optical data indicate a blue shift of the absorption maximum in comparison to the alpha-linked analogues due to cross-conjugation between fused rings. The crystal structures of 3,3'-bi(thieno3,2-b]thiophene) and 3,3';6',3"-ter(thieno-3,2-b]thiophene) reveal edge-to-face pi-stacked dimer motifs, whereas the crystal structure of 3,3'-bis(dithieno3,2-b:2',3'-d]thiophene) consists of face-to-face pi-stacked molecules. structure: see text]