Molecule-substrate interaction changes upon metal inclusion into a porphyrin

In free base TPP molecules the overlap of the phenyl orbitals with the substrate is enhanced through a temperature induced reaction, thus reducing the molecule–to–substrate distance. In the metalated (with Co) compound a strong bond establishes between Co and Ag states, leaving the porphyrin macrocycle to a larger distance from the surface with the phenyls rotated even after the annealing.

G. Di Santo et al., Chem. - A Europ J. 18(40), 12619–12623 (2012)


In the experiment reported here, we investigate the role of Co atoms in the Co-TPP, in situ metalated, and in the CoTPP compounds concerning the interaction between the first molecular layer and the underlying Ag metallic substrate. The spectroscopic characterization of the thin CoTPP molecular layers has been carried out on the “as evaporated” pure compound and in-situ metalated 2HTPP with Co atoms, by exploring the annealing effect on the monolayers from the point of view of the molecular orientation. Our results show that the flat conformation is driven by the geometrical adaptation of the free-base molecule upon annealing before the metal coordination. On the contrary the presence of the metal ion, both in the CoTPP or in the RT metalated Co-TPP, seems to inhibit a more flat configuration when the system is annealed at the same temperature because of the strong interaction of the Co with the Ag metallic substrate.


 

Our experiments show that the presence of a metal atom in the Tetraphenylporphyrin macrocycle influences the adsorption geometry of a molecular monolayer on Ag(111). We have shown that in pristine 2H-TPP monolayer, the bonds between π molecular orbitals and Ag s-p states dominate the interaction and the molecules, with an annealing at  550K, have the tendency to rotate the phenyl legs parallel to the substrate surface. On the contrary, the presence of Co atom in the macrocycle both in the form of Co-TPP and in the room temperature Co metalated TPP show an hybridization between the Co dz2 and Ag s-p states. When Co metalation is done on the molecules with the flat phenyl legs, due to the shorter distance, the hybridization between Co and Ag is stronger and there is an higher density of states near the Fermi level.
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Changing the molecule-substrate interaction
upon metal inclusion into a porphyrin

G. Di Santo, C. Sfiligoj, C. Castellarin-Cudia, A. Verdini, A. Cossaro, A. Morgante, L. Floreano, and A. Goldoni


Chemistry - A European Journal, vol. 18, Issue 40, pages 12619-12623, 1 October 2012 

Article first published online: 22 AUG 2012

DOI: 10.1002/chem.201201640


































               
     

Last Updated on Wednesday, 12 December 2012 13:55