Coordinated H-Bonding between Porphyrins on Metal Surfaces

Abstract

Using a combination of X-ray photoelectron spectroscopy (XPS) and core level shift first principles calculations, we determine the formation of an unusual intermolecular interaction between porphyrin molecules. We show that protoporphyrin IX molecules (H2PPIX) adsorbed on Cu surfaces at low temperature (LT) form molecular adlayers stabilized by a strong (1.3 eV) tetragonal coordinated H-bond. This unconventional H-bonding involves the four nitrogen atoms in the tetrapyrrole macrocycle of one molecule, four hydrogen atoms, and one of the hydroxyl oxygen atoms from the carboxylic acid groups of an adjacent molecule. The calculations demonstrate that the corresponding fingerprint of this bond is observed in both the nitrogen XPS data, showing a unique peak, and the almost unchanged 1s core level energy of the hydroxyl oxygen atoms. We explain the formation of this bond by a charge rearrangement mechanism that includes proton sharing and migration.

Structure of a Water Monolayer on the AnataseTiO2(101)Surface

“…In fact, the hydrogen bond between OH and H 2 O (length 1.71Å) reduces the O-1s binding energy on the coordinated H 2 O molecule by 0.64 eV compared to the other water molecules. The reduction of core-level binding energies by H-bonds is a well-documented effect [22,35]. The broadening and redshift observed in Fig.…”

Surface chemistry of porphyrins and phthalocyanines

“…A complex hydrogen-bonded network consisting of 2HPPIX molecules (see Fig. 4) on various Cu and Au surface was described by Garcia-Lekue et al [507]. [380].…”

Molecular Engineering of Free‐Base Porphyrins as Ligands—The N−H⋅⋅⋅X Binding Motif in Tetrapyrroles

“…[27] It has also been shown that protoporphyrin IX (PPIX, 71)a dsorbed on aC us urface at low temperature forms adlayers stabilized by tetragonal Hbonds between the nitrogen atoms of the macrocycle core and peripherally bound carboxyl groups. [28] Looking at examples in nature,t he malaria pigment hemozoin, ad isposal product from the digestion of blood by malaria parasites,i sa ni nsoluble,p eripherally hydrogen-bonded dimer of b-hematin. [29] And in chlorosomes,p hotosynthetic antenna complexes found in some anaerobic bacteria, hydrogen bonding can have ac ritical influence on exciton dynamics and as such, the light-harvesting process itself.…”

“…Further examples of the directing and reinforcing characteristics of hydrogen bonds are found in porphyrinic solids, self‐assembled monolayers (SAMs), nanofibers and nanorods, and nanochannels of 2,3,5,7,8,10,12,13,15,17,18,20‐dodecaphenylporphyrin (H 2 DPP, 64 ) derivatives . It has also been shown that protoporphyrin IX (PPIX, 71 ) adsorbed on a Cu surface at low temperature forms adlayers stabilized by tetragonal H‐bonds between the nitrogen atoms of the macrocycle core and peripherally bound carboxyl groups …”