Synthesis of Thienoacenes via Cascade Copper-Catalyzed C–S Coupling and Thienannulation Reactions and Their Thermoelectric Properties

Thienoacenes are a prominent class of fused-ring conjugated organic compounds and have attracted considerable attention due to their high coplanarity, good stability, high charge-carrier mobility, etc. However, most current synthetic methods toward thienoacenes require costly starting materials and reagents, as well as a lengthy synthetic procedure with low overall yields. Herein, a nonprecious copper-catalyzed system without additional ligands was developed to facilitate C-S coupling and 5-endo-dig thienannulation reaction, leading to the synthesis of a range of thienoacenes including dithieno[3,2-<i>b</i>:2',3'-<i>d</i>]thiophenes (DTTs) and thieno[2',3':4,5]thieno[3,2-<i>b</i>]thiophene[2,3-<i>d</i>]thiophene (TTAs) with yields of up to 90% (for single-sided thienannulation reactions) and 65% (for double-sided thienannulation reactions). In addition, three π-extended DTTs were studied as potential thermoelectric materials, and their composites with single-walled carbon nanotubes (SWCNTs) exhibited high thermoelectric performance with the power factor up to 399.01 ± 16.26 μW m^-1 K^-2 at room temperature, which is the highest reported for thermoelectric composites comprising small-molecule thiophene derivatives and SWCNTs, signifying a step forward in the development of high-performance thermoelectric composites based on thiophene derivatives.