Narrow band-gap conjugated small molecules and polymers have both been drawing significant attentions in application as organic semiconductors, especially in organic solar cells. An inevitable fact is that, intrinsic advantages and disadvantages of these two classes of materials relevant to solution-processable photovoltaics are often contrary. In particular, small molecules possess monodispersity in chemical structures, higher crystallinity, and ready purification through chromatography, while on the other hand, poorer film formation properties and lower thermal stabilities in the solid state, as compared with their polymeric counterparts. More importantly, solar cell devices based on small molecular materials are extremely sensitive towards chemical impurities, of which polymers are relatively more tolerant. On the other hand, the polydisperse nature of polymers significantly complicates the interpretation of solid state structure, resulting in poor practices towards satisfactory device application. Considering the fact that polymers and small molecules provide complementary material properties, we have designed molecular frameworks with successive extension of donor-acceptor characteristics. The dimension of such molecular structures lie in right between small molecules and polymers, which offers a unique bridge for studying their structure-property correlation while transitioning from shorter to longer molecular lengths. Molecular materials synthesized by following these frameworks are able to extract some of the most important merits from both polymers (e.g., film quality and thermal robustness) and small molecules (e.g., structural monodispersity and crystallinity). A synergistic beneficial effect on device performance has also emerged upon elongation of molecular structures while in conjugation with fluorine substitution. Fabrication of solar cell devices with these materials does not require delicate control over solvent additives or post-deposition treatment, yet reaching power conversion efficiencies of 6~7%. More importantly, some of these molecules are able to be processed from bio-derived green solvent (i.e., 2Me-THF) to give solar cell device efficiency over 5%. While integrated in field effect transistors, the extension of molecular length leads to device thermal stability beyond 200 °C, which can be exceeding 300 °C by simple chemical structure modification.