Understanding the Interaction of the Porphyrin Macrocycle to Reactive Metal Substrates: Structure, Bonding, and Adatom Capture

Abstract

We investigate the adsorption and conformation of free-base porphines on Cu(110) using STM, reflection absorption infrared spectroscopy, and periodic DFT calculations in order to understand how the central polypyrrole macrocycle, common to all porphyrins, interacts with a reactive metal surface. We find that the macrocycle forms a chemisorption bond with the surface, arising from electron donation into down-shifted and nearly degenerate unoccupied porphine π-orbitals accompanied with electron back-donation from molecular π-orbitals. Our calculations show that van der Waals interactions give rise to an overall increase in the adsorption energy but only minor changes in the adsorption geometry and electronic structure. In addition, we observe copper adatoms being weakly attracted to adsorbed porphines at specific molecular sites. These results provide important insights into porphyrin-surface interactions that, ultimately, will govern the design of robust surface-mounted molecular devices based on this important class of molecules.

From Graphene Nanoribbons on Cu(111) to Nanographene on Cu(110): Critical Role of Substrate Structure in the Bottom-Up Fabrication Strategy

“…A similar effect has been recently utilized for adatom capture on metal surfaces 42,45. Nevertheless, further away from GNRs the Br atoms self-assemble in a regular ൫√3 × √3൯ܴ30° structure, characteristic of submonolayer of Br on Cu(111) 46.…”

Surface chemistry of porphyrins and phthalocyanines

“…2HP was also found to capture Cu adatoms in its vicinity, presumably by a substrate-mediated bonding mechanism [436] (cf. Section 5.…”

“…Theoretical treatment of the surface chemical bond of porphyrins and phthalocyanines with DFT methods is hampered by the (presumably) large contribution of van der Waals dispersive interactions, which are not adequately described by standard DFT. However, there is an increasing awareness of this issue, and various approximate corrections have been introduced [544][545][546] and successfully applied to the adsorption of porphyrins [20,365,436] and phthalocyanines [248,330,341,360,547].…”

“…Interestingly, 2HP was found to capture Cu adatoms in its vicinity. The rather long lateral distance of 3.7 Å from a Cu adatom to the closest atom in the molecule excludes formation of direct chemicals bonds; instead, a substrate mediated bonding mechanism was proposed [436].…”

Investigating the molecule-substrate interaction of prototypic tetrapyrrole compounds: Adsorption and self-metalation of porphine on Cu(111)

“…1(a)) is expected to provide a reference for the entire class of porphyrins, but surprisingly little is known about this important parent compound. Only very recently the first efforts were dedicated to fill this gap by studying the interaction of 2H-P molecules with the Cu(110) 33,47 and Ag(111) 48 surfaces. For 2H-P on Cu(110), STM and DFT calculations were employed, whereby the latter indicated a bidirectional electron transfer between molecule and substrate.…”