Search for "dithieno[2,3-b:3',2'-d]thiophene" in Full Text gives 2 result(s) in Beilstein Journal of Organic Chemistry.
Beilstein J. Org. Chem. 2022, 18, 809–817, doi:10.3762/bjoc.18.81
Beilstein J. Org. Chem. 2013, 9, 767–774, doi:10.3762/bjoc.9.87