A Domino Protocol toward High-performance Unsymmetrical Dibenzo[d,d']thieno[2,3-b;4,5-b']dithiophenes Semiconductors.

Unsymmetric organic semiconductors have many advantages such as good solubility, rich intermolecular interactions for potential various optoelectronic applications. However, their synthesis is more challenging due to intricate structures thus normally suffering tedious synthesis. Herein, we report a trisulfur radical anion (S3⋅-) triggered domino thienannulation strategy for the synthesis of dibenzo[d,d']thieno[2,3-b;4,5-b']dithiophenes (DBTDTs) using readily available 1-halo-2-ethynylbenzenes as starting materials. This domino protocol features no metal catalyst and the formation of six C-S and one C-C bonds in a one-pot reaction. Mechanistic study revealed a unique domino radical anion pathway. Single crystal structure analysis of unsymmetric DBTDT shows that its unique unsymmetric structure endows rich and multiple weak S⋅⋅⋅S interactions between molecules, which enables the large intermolecular transfer integrals of 86 meV and efficient charge transport performance with a carrier mobility of 1.52 cm2 V-1 s-1. This study provides a facile and highly efficient synthetic strategy for more high-performance unsymmetric organic semiconductors.

Compositing Benzothieno[3,2-b]Benzofuran Derivatives with Single-Walled Carbon Nanotubes for Enhanced Thermoelectric Performance.

Although numerous thermoelectric (TE) composites of organic materials and single-walled carbon nanotubes (SWCNTs) have been developed in the past decade, most of the research has been related to polymers without much on organic small molecules (OSMs). In this work, benzothieno[3,2-b]benzofuran (BTBF) and its derivatives (BTBF-Br and BTBF-2Br) were synthesized and their TE composites with SWCNTs were prepared. It is found that the highest molecular orbital level and band gap (Eg) of BTBF, BTBF-Br, and BTBF-2Br gradually decrease upon the introduction of electron-withdrawing Br group on BTBF. These changes significantly improve the Seebeck coefficient and power factor (PF) of OSM/SWCNT composites. An appropriate energy barrier between BTBF-2Br and SWCNTs promotes the energy filtering effect, which further contributes to the enhancement of composites' thermoelectric properties. The composites of SWCNTs and BTBF-2Br with the smallest Eg (4.192 eV) afford the best thermoelectric performance with the room temperature power factor of 169.70 ± 3.46 µW m-1 K-2 in addition to good mechanical flexibility and thermal stability. This study provides a feasible strategy for the preparation of OSM/SWCNT composites with improved thermoelectric properties.

Copper-mediated construction of benzothieno[3,2-b]benzofurans by intramolecular dehydrogenative C-O coupling reaction.

An efficient method to synthesize benzothieno[3,2-b]benzofurans via intramolecular dehydrogenative C-H/O-H coupling has been developed. Good to excellent yields (64-91%) could be obtained no matter if the substituted group is electron-donating or electron-withdrawing. Notably, three-to-six fused ring thienofuran compounds could be constructed using this method. A reaction mechanism study showed that 1,1-diphenylethylene can completely inhibit the reaction. Therefore, it is a radical pathway initiated by single electron transfer between the hydroxyl of the substrate and the copper catalyst.