Solution STM images of porphyrins on HOPG reveal that subtle differences in molecular structure dramatically alter packing geometry

Solution STM images are reported for free-base octaethylporphyrin (H2OEP) and the Cu(II) and Zn(II) chelates (CuOEP and ZnOEP) on HOPG in 1,2-dichlorobenzene solution under ambient conditions. H2OEP and CuOEP each form a quasi-square lattice, whereas ZnOEP forms a quasi-hexagonal lattice on the surface. The binary mixture of any two of the porphyrins forms a well-ordered two-layer structure on the HOPG surface, with one species occupying the bridge sites of the array of the other species. All of the mixed adlayers exhibit a quasi-hexagonal lattice with a higher packing density than the single-component adlayers. Collectively, these observations indicate that the structure of the adlayers is controlled by a complex interplay of substrate-molecule and molecule-molecule interactions. Copyright (C) 2005 Society of Porphyrins & Phthalocyanines.