Single-molecule spectroscopic probing of N-heterocyclic carbenes on a two-dimensional metal

Abstract

N-heterocyclic carbenes (NHCs) have recently proven to be powerful ligands for planar surface modification in terms of chemical and electronic properties due to their structural diversity, property tunability, and high affinity for a diverse array of elements. However, the utilization of NHCs for planar surface modification has almost exclusively been limited to bulk substrates. Here, we investigate the adsorption of NHCs on a two-dimensional (2D) metal (i.e., borophene) using combined single-molecule optical/electronic spectroscopy. Tip-enhanced Raman spectroscopy reveals two distinct interfacial states between individual NHCs and borophene, which correspond to covalent (boron–carbon bonding) and van-der-Waals-type interactions. Furthermore, the impact of NHC modification on borophene’s electronic properties is demonstrated by local work function reductions, as measured by scanning tunneling spectroscopy. In addition to providing novel insight into NHC–substrate interactions in the 2D regime, this study opens up an avenue for investigations of single-molecule NHC chemistry.