Chiral Expression at the Solid-Liquid Interface : A Joint Experimental and Theoretical Study of the Self-Assembly of Chiral Porphyrins on Graphite

The chiral organization of an enantiopure functional molecule on an achiral surface has been studied with the aim of understanding the influence of stereogenic centers on the self-assembly in two dimensions. A chiral tetra meso-amidophenyl-substituted porphyrin containing long hydrophobic tails at the periphery of the conjugated π-electron system was prepared for this purpose. Scanning tunneling microscopy (STM) images of the compound at the graphite−heptanol interface reveal a chiral arrangement of the molecules, with the porphyrin rows tilted by 13° with respect to the normal to the graphite axes. In terms of molecular modeling, a combination of molecular dynamics simulations on systems constrained by periodic boundary conditions and on unconstrained large molecular aggregates has been applied to reach a quantitative interpretation on both the density of the layer and its orientation with respect to the graphite surface. The results show clearly that (i) the methyl groups of the stereogenic point toward...