Conformation-Dependent Stacking Behavior of Porphyrin Assemblies Observed by Using Scanning Tunneling Microscopy

We present a scanning tunnelling microscopy Study on the supramolecular ordering of 21,23-dihydro-5,10,15,20-tetrakis(4-(ethyl 11-phenoxyundecanoate) porphyrin (ester alkyl-TTPP) molecules on a highly oriented pyrolytic graphite surface. Ester alkyl-TTPP formed a molecular superlattice structure-an alternating single/double layer pattern on a graphite surface. Two types of adsorption conformations were observed. On the basis of the theoretical calculation and combined with our previous investigations, it is concluded that the molecular adsorption conformation has an appreciable effect on the interactions of molecule-molecule and molecule-substrate after introducing an ester group into the aliphatic chain. Theoretical investigation indicates that the pi-pi interactions between the porphyrin cores together with the van der Waals interaction between alkyl chains direct the stacking behavior of ester alkyl-TTPP molecules.