Synthesis and crystal structures of unsymmetrical wave-shaped heptathienoacenes.

Three unsymmetrical wave-shaped heptathienoacenes (UHT-1, UHT-2 and UHT-3) with sulfur atoms at different isomeric locations in the two terminal thiophene rings were designed and synthesized. The synthetic strategy contains two crucial steps, including the cross-coupling of two different dithienothiophene isomers (DTT) from dithieno[2,3-:3',2'-]thiophene (-DTT), dithieno[2,3-:2',3'-]thiophene (-DTT) and dithieno[2,3-:3',4'-]thiophene (-DTT) as building blocks through the Negishi coupling and intramolecular cyclization reactions with (SnBu)S. X-ray crystal structures of UHT-1, UHT-2 and UHT-3 show that the molecules adopt a wave-shaped geometry with multiple intermolecular interactions, such as S-S, S-C and S-H, which result in different crystal packing patterns. The isomeric location of the sulfur atoms of the two terminal thiophene rings of UHT-1, UHT-2 and UHT-3 plays an important role in tuning π-electronic conjugation and spectroscopic behaviors.