Recyclable terthiophenes for synthesizing precision conjugated oligomers†

Precision polymers and oligomers are distinguished by their well-defined characteristics (e.g., chain length, monomer sequence). As a result, they have been leveraged in recent years to study numerous structure–property relationships ranging from photophysical characteristics to antimicrobial activity. However, the synthesis of precision polymers and oligomers often requires elaborate building blocks that are compatible with specific polymerization approaches. In most cases, these building blocks are neither recovered nor recycled, limiting the efficiency and sustainability of these synthetic methods. Herein, we report the first synthesis of a thiophene-bearing nickel(ii) external initiator that is used to synthesize modular and regioregular terthiophene. We then show that the halogenated terthiophene is a compatible building block in synthesizing precision oligothiophenes. This thiophene-bearing external initiator exhibits remarkable reactivity and stability through polymerization. Furthermore, we show that excess halogenated terthiophene can be recovered post-oligomerization and reused in subsequent syntheses. Overall, this work highlights the feasibility of synthesizing all-thiophene polymers using thiophene-bearing external initiators and recycling the modular terthiophene after oligomerization.