Planar β-Linked Oligothiophenes Based on Thieno[3,2-<i>b</i>]thiophene and Dithieno[3,2-<i>b</i>:2‘,3‘-<i>d</i>]thiophene Fused Units

A series of planar β-linked oligothiophenes based on thieno[3,2-b]thiophene and dithieno[3,2-b:2‘,3‘-d]thiophene fused units were synthesized. The optical data indicate a blue shift of the absorption maximum in comparison to the α-linked analogues due to cross-conjugation between fused rings. The crystal structures of 3,3‘-bi(thieno[3,2-b]thiophene) and 3,3‘;6‘,3”-ter(thieno-[3,2-b]thiophene) reveal edge-to-face π-stacked dimer motifs, whereas the crystal structure of 3,3‘-bis(dithieno[3,2-b:2‘,3‘-d]thiophene) consists of face-to-face π-stacked molecules.