Ubiquitous deprotonation of terephthalic acid in the self-assembled phases on Cu(100)

QUIROGA ARGAÑARAZ, BERNARDA; CRISTINA, LUCILA; RODRÍGUEZ, LUIS M; COSSARO, ALBANO; VERDINI, ALBERTO; FLOREANO, LUCA; FUHR, J. D.; GAYONE, J. ESTEBAN; ASCOLANI, HUGO

PHYSICAL CHEMISTRY CHEMICAL PHYSICS

ROYAL SOC CHEMISTRY

Año: 2018

1463-9076

We performed an exhaustive study of terephthalic acid (TPA) self-assembly on the Cu(100) surface, where first-layer molecules display two sequential phase transitions in the 200 - 400 K temperature range, corresponding to different stages of molecular deprotonation. We followed the chemical and structural changes by means of high-resolution X-ray photoelectron spectroscopy (XPS) and variable-temperature scanning tunneling microscopy (STM), which were interpreted on the basis of density functional theory (DFT) calculations and photoemission simulations. In order to disentangle the spectroscopic contribution of molecules in different states of deprotonation, we modified the substrate reactivity by deposition of a small amount of Sn, which hampers the deprotonation reaction. We found that the characteristic molecular ribbons of the TPA/Cu(100) α-phase at low temperature contain a significant fraction of partially deprotonated molecules, contrary to the expectation of a fully protonated phase, where the self-assembly was claimed to be simply driven by intermolecular double hydrogen bonds [OH · · · O]. On the basis of our simulations, we propose a model where the carboxylate groups of the partially deprotonated molecules form single hydrogen bonds with the carboxylic groups of fully protonated molecules. By real time XPS, we also monitored the kinetics of the deprotonation reaction. We show that the network of mixed single and double hydrogen bonds inhibits further deprotonation up to ∼ 270 K, whereas isolated molecules display a much lower deprotonation barrier.