Modulating Morphology of Thiol-Based Monolayers in Honeycomb Hydrogen-Bonded Nanoporous Templates on the Au(111) Surface: Simulations with the Modified Force Field

Abstract

The difference in monolayer morphology caused by different functional thiols (ASH, BP3SH, and C12SH) within the surface-supported porous network of naphthalene tetracarboxylic di-imide (NDI) and melamine (MEL) molecules has been investigated by molecular dynamics simulations with the modified force field. The hydrogen-bonded bimolecular network is taken as the template when different thiols are deposited on the Au(111) surface. Force field parameters of intermolecular (NDI–NDI, MEL–MEL, NDI–MEL, and thiol–thiol) and interfacial (Au···S) interactions are modified to reproduce MP2 potential energy curves and the adsorption height. Interfacial interactions between the network and the Au(111) surface support the NDI–MEL bimolecular template, lying flat in an ordered hexagonal pattern on the substrate. The packing morphology of the triple hydrogen-bonded network obtained from molecular dynamics simulations and quantum chemical calculations matches the image from the scanning tunneling microscope. The backbone flexibility, which varies with the length and shape of thiol chains, is demonstrated to affect the monolayer morphology. The packing arrangement tends to be more ordered with the increase of the coverage for alkane thiols. The subsequently deposited thiols also disturb the bicomponent nanopore to a different extent, originating from the subtle balance between the thiol–thiol, thiol–template, and the intratemplate hydrogen-bonding interactions. It is demonstrated that the aromatic rings in BP3SH add a chance to perturb the host network through the π···π stacking in low coverage. The understanding of nanotemplate effect on the thiol-based monolayer growth is helpful for fabricating novel surface-supported host–guest hybrid nanodevices at the single molecular level