Natural photosystems showcase the importance of supramolecular organization for advanced functional properties. Nevertheless, the development of molecular materials by chemists is still mostly initiated by purely molecular considerations whilst the influence of intermolecular couplings on function is only addressed at a later stage. For a period of more than twenty years our group has explored an alternative approach. Thus, we have studied the formation of molecular aggregates and the functional properties originating from the interaction of π-systems in terms of structure-function relationships. In this lecture I will showcase examples from our most recent research on perylene bisimide (PBI) dyes as well as smaller and larger polycyclic aromatic (multi-)imides for which we could accomplish structurally well-characterized supramolecular aggregate structures and obtain insight into their photofunctional properties. With the advancement of our knowledge, recently also tailored supramolecular environments are utilized for the engineering of desired functional properties in molecular aggregates which includes (circularly polarized) fluorescence, phosphorescence and thermally activated delayed fluorescence. Finally, a porous nanographene bilayer will be shown that provides insight on the halide permeation through a single benzene defect.