Local adsorption structure and bonding of porphine on Cu(111) before and after self-metalation

TL;DR

This study combines experimental photoelectron diffraction and DFT calculations to analyze the adsorption structure and bonding of porphine molecules on Cu(111), revealing how metalation affects molecular geometry and surface interactions.

Contribution

It provides the first combined experimental and theoretical analysis of porphine adsorption and metalation on Cu(111), highlighting structural changes and adsorption behavior.

Findings

Adsorption occurs with the molecule center above a surface bridge site.

Metalation changes the corrugation of nitrogen atoms in the macrocycle.

The N atom height increases from 2H-P to cobalt porphine, with an inverse relation to adsorption strength.

Abstract

We have experimentally determined the lateral registry and geometric structure of free-base porphine (2H-P) and copper-metalated porphine (Cu-P) adsorbed on Cu(111), by means of energy-scanned photoelectron diffraction (PhD), and compared the experimental results to density functional theory (DFT) calculations that included van der Waals corrections within the Tkatchenko-Scheffler approach. Both 2H-P and Cu-P adsorb with their center above a surface bridge site. Consistency is obtained between the experimental and DFT-predicted structural models, with a characteristic change in the corrugation of the four N atoms of the molecule's macrocycle following metalation. Interestingly, comparison with previously published data for cobalt porphine adsorbed on the same surface evidences a distinct increase in the average height of the N atoms above the surface through the series 2H-P, Cu-P, cobalt porphine. Such an increase strikingly anti-correlates the DFT-predicted adsorption strength, with 2H-P having the smallest adsorption height despite the weakest calculated adsorption energy. In addition, our findings suggest that for these macrocyclic compounds, substrate-to-molecule charge transfer and adsorption strength may not be univocally correlated.