Facile Synthesis of Dithienobenzothiadiazoles and D18−Cl Polymer via Na2S‐Mediated Rapid Thiophene‐Annulations for Organic Solar Cells.

We present a novel synthetic route for the rapid construction of dithieno[3′,2′:3,4;2′′,3′′:5,6]benzo[1,2‐c][1,2,5]thiadiazoles via Na2S‐promoted thiophene annulation. This method facilitated the synthesis of D18−Cl polymer, known for its efficacy as a polymer donor in bulk‐heterojunction polymer solar cells. Starting from commercially available 4,7‐dihalo‐5,6‐difluorobenzo[c][1,2,5]thiadiazole, various 4,7‐dialkynylated compounds were obtained through Sonogashira reaction conditions. Subsequent Na2S‐promoted thiophene annulations yielded DTBT and its derivatives in excellent yields within 10 minutes. DTBT was then utilized as a precursor for the concise synthesis of D18−Cl, benefiting from reduced synthetic steps, mild reaction conditions, decreased complexity, and high overall yields. In another route, a space group‐bridged DTBT was directly constructed via Na2S‐promoted thiophene annulations and converted into D18−Cl through a couple of steps. This developed protocol offers a straightforward and reliable synthetic tool, conducive to reducing complexities in the production of DTBT‐based organic electronic materials, thereby advancing the potential commercialization of organic solar cells. [ABSTRACT FROM AUTHOR]