Facile Synthesis of Dithienobenzothiadiazoles and D18-Cl Polymer via NaS-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 NaS-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 NaS-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 NaS-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.