In this work, heterogeneous structures consisting of copper porphyrins and tetracene are investigated mainly by photoemission electron microscopy (PEEM) in the vicinity of small silver nanoparticles. As shown for silver clusters on a pristine silicon surface, an important effect is strong coupling to the substrate leading to dramatically altered plasmonic properties which have to be treated beyond the commonly employed dipole approximation. By utilizing the plasmonic properties of the nanoparticles, it was possible to locally excite molecular aggregates by the enhanced plasmonic near-field.