The development of new electron-accepting π-conjugated systems for application as nonfullerene acceptors in organic solar cells (OSCs) is urgently needed. Although π-conjugated systems based on naphtho[1,2-c:5,6-c']bis[1,2,5]thiadiazole (NTz) and naphthalimide (Np) as central and terminal units, respectively, represent possible candidates for nonfullerene acceptors, our knowledge of the structure-property-device performance relationship of these compounds remains limited. We report herein on an investigation of the effect of the substituents on the thiophene (T) linker between NTz and Np on the properties and photovoltaic performance. The photophysical and physicochemical measurements showed that the absorption behavior as well as frontier-orbital energy levels can be fine-tuned by the choice of the substituent on the thiophene rings. Bulk-heterojunction-type OSCs based on these acceptors under blending with poly(3-hexylthiophene) as a donor showed various power conversion efficiencies, ranging from 0.26 to 2.14%. The substituents on the thiophene rings also have a significant influence on the blend film properties, which explain the differences in the short-circuit current densities and fill factors in the OSCs. These results indicate the importance of molecular design in preparing nonfullerene acceptors with NTz and Np units in terms of tuning both the molecular properties of the materials and donor-acceptor interface engineering in the blended films.