The long term scientific aim of the collaborative research center is the rational development of new organic semiconductors focussing on a large and widely variable class of compounds, N-heteropolycycles, which derive from a limited number of fundamental structural building blocks. A precondition for the implementation of this research program is the detailed understanding of the underlying elementary processes. These include the weak intermolecular interactions governing molecular aggregation, electronic excitation and charge transfer, the morphology at interfaces as well as the resulting charge separation. The planned research encompasses the whole spectrum of chemical synthesis, physical, spectroscopic and theoretical characterization of the organic semiconducting materials as well as their material properties reflected in the performance of (opto-)electronic devices. The aim will be to identify the key construction principles that permit a rational control of the molecular properties as well as the characteristics of the resulting material through the combination of theory and experiment. The result of this research effort should be a set of rules for the targeted modification of structure, crystal packing and morphology which would enable a rational access to new materials for organic electronics.