Metalloporphyrins are an important class of organic molecules due to their potential applications in spintronics, data storage and organic solar cells etc. In order to exploit the potential of these molecules it is important to understand the self assembly of these molecules on different substrates and the underlying mechanisms which govern the interfacial interaction and orientation of molecules on surfaces. Recently it has been shown that porphyrin molecule were able to switch net magnetic moment reversibly with magnetic field mediated by a graphene buffer layer.DFT calculations also show that graphene can be used as spin manipulator for iron porphyrin molecules.
In this work we have studied the self assembly of Cl-FeTPP molecules on Gr/Ni(111) and HOPG in order to decipher the influence of substrate on the interfacial electronic properties of Cl-FeTPP molecules. Our analyses reveal significant differences in the interface energetics for the adsorption of FeTPP-Cl on HOPG and Gr/Ni(111) due to unique molecule-substrate interactions. At low coverages significant down shift in the work function for the FeTPP-Cl and Gr/Ni(111) interface is observed suggesting a dipole induced potential step at the interfaces due to stronger molecule-substrate interactions. Valence band analyses shows the existence of interfacial state near Fermi level for the adsorption of FeTPP-Cl on Gr/Ni(111) while no interfacial state is observed for the adsorption on HOPG . Moreover alterations in the work function are feeble for the FeTPP-Cl and HOPG suggesting a weaker molecule–substrate interactions. NEXAFS results shows a change Iron oxidation from +3 to +2 for low coverages clearly indicating a substrate induced dechlorination of Cl-FeTPP for both the substrates however XPS results indicate towards partial dechlorination on Gr/Ni(111) with chlorine being detectable at low ceverages. In case of HOPG molecule coupling appears to be mediated via the π electronic system of substrate, in the absence of covalent bond between molecule and substrate. Unoccupied states at the interfaces are also studied using inverse photoemission spectroscopy revealing the influence of substrate on LUMO position with respect to Fermi level. Our analyses shows that unique band structure of the substrate influence the adsorption mechanism of Cl-FeTPP molecules with HOPG interacting weakly with Cl-FeTPP while stronger molecule–substrate interactions of Gr/Ni(111) are mainly driven by the central Iron atom.
 D. Klar et.al.Physical Review B 89, 144411 (2014).
 S. Bhandary, S. Ghosh, H. C. Herper, H. Wende, O. Eriksson, and B. Sanyal, Phys. Rev. Lett. 107, 257202 (2011).