Quinoidal Oligothiophenes Having Full Benzene Annelation: Synthesis, Properties, Structures, and Acceptor Application in Organic Photovoltaics.

To achieve a complete closed-shell quinoidal state, bis(dicyanomethylene)-substituted quinoidal terthiophenes bearing benzene annelation at all thiophene rings were synthesized using a retro-Diels-Alder reaction as the key step. The unique structures and properties originating from the full benzene annelation were revealed by X-ray analysis as well as property measurements. Organic solar cells based on the combination of a donor polymer with a quinoidal terthiophene as an acceptor showed a power conversion efficiency of 1.39%.