Organic semiconductors are a promising class of materials for low-cost (opto)electronic applications. Since most applications of these materials rely on their optical and (photo)conductive properties, a good understanding of the photophysics of these materials is needed to aid in the development of next generation materials. Our recent studies, which were conducted to gain insight on the photophysical properties and molecular interactions of novel high-performance organic semiconductor materials, will be presented. In particular, effects of donor/acceptor interactions on charge photogeneration and charge transport in composite organic films will be discussed. Our efforts towards understanding intermolecular interactions at nanoscales will also be presented.