Photoelectron spectroscopy investigation of the temperature-induced deprotonation and substrate-mediated hydrogen transfer in a hydroxyphenyl-substituted porphyrin

Abstract

The temperature dependent stepwise deprotonation of 5,10,15,20-tetra(p-hydroxyphenyl)porphyrin is investigated using photoelectron spectroscopy. An abundance of pyrrolic relative to iminic nitrogen and a decrease in the ratio of the amount of −NH− to −N= with increasing annealing temperature is found. In contrast to the molecules adsorbed on Au(111), on the more reactive Ag(110) surface, partial dissociation of the hydroxyl groups and subsequent diffusion and rebonding of hydrogen to the central nitrogen atoms resulting in a zwitterionic molecule was clearly observed. Moreover, partial C−H bond cleavage and the formation of new covalent bonds with adjacent molecules or the surface starts at a relatively high annealing temperature of 300 • C. This reaction is identified to occur at the carbon atoms of the pyrrole rings, which leads also to a shift in the N 1s signal and changes in the valence band of the molecules. Our results show that annealing can significantly alter the molecules which were deposited depending on the maximum temperature and the catalytic properties of the specific substrate. The thermal stability should be considered if a molecular monolayer is prepared from a multilayer by desorption, or if annealing is applied to enhance the self-assembly of molecular structures.

Control of Molecule–Metal Interaction by Hydrogen Manipulation in an Organic Molecule

“…22 More recently, a self-metalation on an inert substrate has been evidenced. 23 Our data suggest that TPP molecules can also strongly interact with a Au(111) surface such that a gold atom of the surface can be lifted toward the center of the macrocyle. The HOMO−LUMO gap of the TPP molecule interacting with the surface is reduced as compared to H 2 TPP and HTPP.…”

“…The picking up of a substrate atom by a H 2 TPP molecule has been previously observed on iron and nickel surfaces . More recently, a self-metalation on an inert substrate has been evidenced . Our data suggest that TPP molecules can also strongly interact with a Au(111) surface such that a gold atom of the surface can be lifted toward the center of the macrocyle.…”

Quantum Tunneling Mediated Interfacial Synthesis of a Benzofuran Derivative

“…For T ann = 200 K, we observed ab road O1sp eak containing two convoluted components.T he binding energies E B of these two peaks are 533.6 and 534.3 eV,which agree well with literature values for phenol and furan species adsorbed on Ag surfaces. [18] Annealing freshly prepared samples at higher temperatures results in an increased intensity of the furan contribution, which becomes prevalent at T ann = 350 K. TheXPS data thus not only support the proposed hydroalkoxylation scenario, but also exclude deprotonation of the hydroxy group as ad ominant effect, [19] since prominent features between 532 and 530 eV are absent.…”

Selective coordination with heterogeneous metal atoms for inorganic–organic hybrid layers

“…Here, the increase in pyrrolic nitrogen can be explained by the presence of the peripheral electron-donating substituents and the delocalization of electrons in the iminic nitrogen (]N-) of porphyrin. 25,26 Signicantly, the peak positions of both iminic and pyrrolic nitrogen were unchanged when using various Sn(btsa) 2 exposure times, and the peak associated with the metal-nitrogen bond was not observed. These results conrmed that Sn atoms were not combined with four nitrogen atoms in the center of the porphyrin.…”