Quinoidal oligothiophenes have attracted great attention as promising electron-transporting semiconductors. However, the use of quinoidal molecules as nonfullerene acceptors (NFAs) in organic solar cells has not been reported so far. We hypothesized that control of diradical characteristics to fine-tune the electronic properties of quinoidal oligothiophenes is important for the application to NFAs. Since the representative approach to increase the contribution of the quinoid character is the utilization of aromatic stabilization in a quinoidal form, we designed and developed new quinoidal oligothiophenes that contain benzene annelation. As a result, we revealed that quinoidal terthiophenes having fully benzene annelation functioned as NFAs. Furthermore, the quinoidal thiophene 5-mer showed acceptor characteristics in NIR organic phototransistors. In this presentation, we also discuss the influence of benzene annelation on the diradical character and physical properties.