Self-assembly of metal free porphyrin layers at copper-electrolyte interfaces: Dependence on substrate symmetry

Combined Cyclic Voltammetry (CV) and in-situ Electrochemical Scanning Tunneling Microscopy (EC-STM) studies were employed to compare the self-assembly of redox-active 5,10,15,20-Tetrakis (4-trimethyl ammonium phenyl) porphyrin tetra (p-toluenesulfonate), abbreviated as [H2TTMAPP]+ 4 on Cu(100) and Cu(111) electrode surfaces in 10 mM HCl solution. Under these conditions, both surfaces are chloride pre-covered with a c(2 × 2) Cl- and c p × 3 Cl-layer on Cu(100) and Cu(111), respectively. On both surfaces highly ordered [H2TTMAPP]+ 4 layers are spontaneously formed. The short range molecular arrangement is quadratic in nature on both surfaces which can be described by a 58 × 58 R23° unit cell on the c(2 × 2) Cl-Cu(100), and a (3 × 4) unit cell on the c p × 3 Cl-Cu(111) substrate. Large scale domains are formed on both surfaces the orientation of which reflects the symmetry of the substrate, namely on Cu(100) [Cu(111)] equivalent domains are rotated by 90° [120°], respectively. Thus, the different symmetry of the respective substrate surface has an influence on the otherwise self-assembled organic molecules.