Probing Interfacial Electronic Effects on Single-Molecule Adsorption Geometry and Electron Transport at Atomically Flat Surfaces

Clarifying interfacial electronic effects on molecular adsorption is significant in many chemical and biochemical processes. Here, we used STM breaking junction and shell-isolated nanoparticle-enhanced Raman spectroscopy to probe electron transport and adsorption geometries of 4,4 '-bipyridine (4,4 '-BPY) at Au(111). Modifying the surface with 1-butyl-3-methylimidazolium cation-containing ionic liquids (ILs) decreases surface electron density and stabilizes a vertical orientation of pyridine through nitrogen atom sigma-bond interactions, resulting in uniform adsorption configurations for forming molecular junctions. Modulation from vertical, tilted, to flat, is achieved on adding water to ILs, leading to a new peak ascribed to CC stretching of adsorbed pyridyl ring and 316 % modulation of single-molecule conductance. The dihedral angle between adsorbed pyridyl ring and surface decreases with increasing surface electronic density, enhancing electron donation from surface to pyridyl ring.

Automated summary

By utilizing STM breaking junction and shell-isolated nanoparticle-enhanced Raman spectroscopy, researchers investigated the electron transport and adsorption geometries of 4,4'-bipyridine on Au(111). The surface modification with ionic liquids containing specific cations was found to influence the adsorption configurations of the molecules and their single-molecule conductance, with water addition resulting in significant changes. The dihedral angle between the adsorbed pyridyl ring and the surface was observed to decrease with increasing surface electronic density, enhancing electron donation from the surface to the pyridyl ring.