Experimental and vdW-DFT Study of the Structure, Properties, and Stability of Isonicotinic Acid Self-Assembled Monolayers on Gold

Abstract

Self-assembling of derivatized aromatic molecules on metals is of interest in the generation of modified surfaces with ionizable groups in order to generate charged surfaces for constructing more complex nanostructured interfaces. In the present contribution we explore the structure, properties, and stability of isonicotinic acid (INA) adsorbed on gold surfaces employing electrochemical and spectroscopic methods as well as DFT calculations at the level of van der Waals interactions (vdW-DFT). Electrochemical results show changes in the kinetics of redox probes due to the self-assembled monolayers (SAMS) formation on the gold surface. Furthermore, SERS experiments indicate that INA species adsorb on gold perpendicularly to the surface through the deprotonated carboxylate group. In addition, due to the ionizable groups involved in the molecular anchorage, some instability of the SAMS of INA is obtained by pH modification of the chemical environment. On the other hand, theoretical calculations indicate that a strong interaction of the carboxylate group to the gold surface at the bridge sites takes place, and the adsorbed species have sufficient mobility at room temperature. The effect of the coverage and the stability of the SAMS are also reported.