We demonstrate the concept of controlling phase separation behavior through designing directional intermolecular interactions. The twisted molecular configuration and intermolecular hydrogen bonds result in PBI-1 self-assembly into nanofiber aggregates of the order of tens of nanometers. In the blend of Zn-mTNP and PBI-1, the charge transfer interaction was suppressed effectively due to the unfavored π–π stacking for their twisted and planar molecular configurations. The spin-coated films of Zn-mTNP, PBI-1 and their blend have been characterized by UV-vis absorption spectra, and atomic force microscopy, revealing that the preferred phase separation structures in the nano scale were obtained.