Self‐Assembled Monolayers of N‐Heterocyclic Olefins on Au(111)

Abstract

Self‐assembled monolayers (SAMs) of N‐heterocyclic olefins (NHOs) have been prepared on Au (111) and their thermal stability, adsorption geometry, and molecular order were characterized by X‐ray photoelectron spectroscopy, polarized X‐ray absorption spectroscopy, scanning tunneling microscopy (STM), and density functional theory (DFT) calculations. The strong σ‐bond character of NHO anchoring to Au induced high geometrical flexibility that enabled a flat‐lying adsorption geometry via coordination to Au‐adatom. The flat‐lying adsorption geometry was utilized to further increase the surface interaction of NHO monolayer by backbone functionalization with methyl groups that induced high thermal stability and a large impact on work function values, which outperformed that of N‐heterocyclic carbenes. STM measurements, supported by DFT modeling, identified that NHOs were self‐assembled in dimers, trimers, and tetramers constructed of two, three, and four complexes of NHO‐Au‐adatom. This self‐assembly pattern was correlated to strong NHO‐Au interactions and steric hindrance between adsorbates, demonstrating the crucial influence of the carbon‐metal σ‐bond on monolayer properties.