Synthesis and Design of Thiophene Materials: Effects of Ring Fusion and Metal Coordination

Abstract

Conjugated organic materials comprise a field of materials chemistry focused on the development of semiconducting organic plastics, popular applications of which are plastic solar cells and display technologies. One of the reasons these materials have gained so much attention is that their optical and electronic properties can be tuned through engineering at the molecular level. Thiophene, an aromatic heterocycle, is a popular building block in the synthesis of many conjugated materials, prized for both the ease in which it can be synthetically functionalized and its ability to form highly conductive and low band gap materials. The Rasmussen group has previously reported on the generation of two classes of materials, the inorganic metal thiophenedithiolenes and the fused-ring heterocycle unit thieno[3,4-b]pyrazine (TP), both of which have applications in conducting materials. In an effort to expand upon the applicability and versatility of these materials, a series of interconnected projects were performed to further tune their optical, electronic, and physical (e.g. solubility) properties. This involved synthetic molecular design, including judicious consideration of structure-function relationships, and characterization of the resulting materials. Highlights include a sterics vs. electronics consideration of the catalyzed hydrodebromination of the molecular building-block 2,3,5-tribromothiophene, variation of the coordinating metal in thiophenedithiolenes to tune the optics and electronics, and characterization of the effects of ring-fusion on TP-based terthienyl homopolymers. Additionally, a new application of the TP monomer was found, whereby it was successfully incorporated as a bridging ligand into a multi-metallic Ru(II) supramolecular assembly, which demonstrated good metal-metal communication.