Heterocycle substitution can have a dramatic, and potentially unintended, impact the physical, optical, electrochemical, and photovoltaic properties of donor materials used in organic electronics. A change as small as a heteroatom substitution up or down a group can selectively tune energy levels by either stabilizing or destabilizing them, resulting in wider or narrower bandgaps. Along the same lines, a substitution with a heteroatom from a different group can completely reverse the role of a building block from being π-electron acceptor to a π-electron donor. Full heterocycle substitution can further be used to tune the absorption of materials, by playing on strength of aromaticity. This dissertation reports the synthesis and characterization of various π-conjugated systems, and examines the role heterocycle substitution plays on the optical, electrochemical, and photovoltaic properties of the materials.