Copper-Octaethyl Porphyrin self-assembly has been studied on NaCl islands, 1-3 monolayers thick, grown oil metal substrates. Extended ordered molecular monolayers are observed for the first time on ultrathin insulator films. The assembly occurs in hierarchical fashion, starting oil the metal substrate, then followed by assembly on the first and second NaCl layers, clearly demonstrating a decrease in adsorption energy for increasing insulator layer thickness. The underlying mechanisms are discussed oil the basis of molecule-substrate interactions. Voltage-dependent STM images reveal differences of the electronic structure for molecules adsorbed on metal and NaCl/metal areas. (c) 2005 Elsevier B.V. All rights reserved.