Synthesis of Benzo[1,2-b:3,4-b′:5,6-b″]trithiophenes via C–H Thienannulation for High Performance Thermoelectric Composites with Single-Walled Carbon Nanotubes

As a type of organic small molecule (OSMs), the introduction of sulfur atoms in fused-ring thiophenes can reduce the dihedral angle between fused rings, which helps to form planar structures and makes it easier to form tightly packed crystal structures, creating more continuous paths for charge transfer. Therefore, they have aroused widespread research interest. However, little research has been conducted on benzo[1,2-b:3,4-b′:5,6-b″]trithiophenes (BTTs), and their simple and efficient syntheses still need to be urgently developed. Herein, we have developed a synthetic approach for BTTs via C–H thienannulation. This protocol features streamlined domino synthetic procedures, eliminating the requirement for the introduction of halogen functional groups, catalysts, and additives. BTTs exhibit planar structures, enabling tight crystal packing that creates a continuous pathway for charge transport. These structural attributes endow BTTs with substantial promise for application in organic electronic materials. Therefore, 2,5,8-tris(4-propylphenyl)benzo[1,2-b:3,4-b′:5,6-b″]trithiophene ((C3-Ph)3-BTT) and its brominated derivative ((C3-Ph)3-Br3-BTT) were investigated as organic small molecules (OSMs) for doping with single-walled carbon nanotubes (SWCNTs) to fabricate OSM/SWCNT composite thermoelectric materials. The composite films exhibited excellent thermoelectric performance, achieving a maximum power factor of 515.23 ± 3.54 μW m–1 K–2 at room temperature. This value represents the highest reported power factor for thiophene derivative/SWCNT thermoelectric composites, marking a significant advancement in the development of high-performance composite thermoelectric materials based on thiophene derivatives.