Organic semiconductors have many applications in portable, large-area or ubiquitous electronics. They also have great potential in bioelectronics as active materials in sensors or transducers. All such devices work by transporting charges; finding materials with large charge mobilities is therefore a major goal in the field of organic electronics. The search for high-mobility organic semiconductors, however, is still largely conducted with an Edisonian philosophy. The primary goal of the proposed activity is the development of a set of rational design principles for creating high-mobility conjugated homopolymers and copolymers which will impact all applications of organic semiconductors, from solar cells to light-emitting diodes and transistors. Insight derived from theory will be used to design and synthesize molecules that will be analyzed experimentally using X-ray diffraction for structural characterization and optical spectroscopy for measuring charge delocalization. These attributes will be correlated with the ability of the materials to carry current. The ultimate goal is to link specific features of the molecular structure and of the short-range arrangement of molecules within the assembly to carrier mobility. The methods developed, both theoretical and experimental, can potentially streamline the search for high mobility polymers and pave the way for the next generation of high-performance organic-based electronic devices.