AbstractRecently porphyrin‐based molecules have proven to be promising candidates to form self‐assembled structures on insulating surfaces. Their close similarity to hemoglobin and chlorophyll‐based molecules makes them promising candidates for functional building parts in molecular electronics. To analyze their opto‐electronic activity, new measurement methods have to be applied. We investigated the formation of such molecular assemblies on ultrathin insulating films by means of a room temperature non‐contact atomic force microscope (NC‐AFM) in combination with a Kelvin probe force microscope (KPFM). As a substrate we used a Cu(111) surface, where either ultrathin KBr or NaCl films are deposited. On those surfaces the evaporated cyano‐porphyrins are forming one‐ and two‐dimensional structures that are comparable to the ones observed on bulk alkali halides. The simultaneously measured surface potential clearly shows a material contrast between the molecules and the insulating films. Finally, we succeeded in obtaining variations of the surface potential induced by the molecular assemblies at the molecular level.