Revealing the Interplay Between Covalent and Non-Covalent Interactions Driving the Adsorption of Monosubstituted Thiourea Derivatives on the Au(111) Surface

摘要

This work reports a detailed study of the adsorption of thiourea and seven monosubstituted thiourea derivatives on the Au(111) surface based on self-consistent periodic density functional theory (DFT) calculations. We included in our analysis the most stable cis and trans configurations for each considered monosubstituted derivative. Different functional groups have been selected for the derivatives in order to address the electron-donating/withdrawing effect on the strength of the molecule-metal interaction. The comparison of the cis- and trans-derivatives revealed interactions of different nature between the molecules and the Au(111) surface. We have been able to disentangle these interactions analyzing the charge density difference plots, the projected density of states (pDOS) and the Non-Covalent Interactions (NCI). For the non-substituted thiourea and all the studied derivatives, besides the strong S-Au bond, it has been observed an Au center dot center dot center dot H-N interaction similar to a hydrogen bonding, which is caused by the charge transfer from the molecules to the Au(111) surface inducing a charge counterbalancing: Au delta-H delta+N delta-. Furthermore, pi-Au interactions between the functional group of the derivatives and the Au(111) surface, mainly observed for the cis-derivatives, were highlighted by the NCI plots. In some particular cases it was also possible to distinguish long-range interactions of the type lone pair-Au. The present results provide insight into a new kind of organic molecule-metal surface interaction, opening the way for the synthesis of potential nanodevices with diverse applications such as sensing (biosensors or atmospheric sensors), optoelectronics, pollution control, or energy conversion.