The self-assembly of long-alkyl-chain substituted phenanthroline derivatives on highly oriented pyrolitic graphite(HOPG) and gold(111) is compared. Whereas the adsorption on HOPG is controlled by the affinity of alkyl chainsfor the substrate, which leads to flat-lying adsorbed molecules, alignments of upright-oriented molecules are formedon gold(111). This situation is explained by the bonding of chelating species with gold(111) surfaces and by theπ-stacking interaction between conjugated moieties. This intermediate situation between strong thiol-like chemicalbonding and the weak n-alkane-like physical adsorption opens the route toward laterally organized functional molecularassemblies.