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 a gold adatom. The flat-lying adsorption geometry was utilized to further increase the surface interaction of the 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 the 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.
Bibliographical noteFunding Information:
This research was supported by the European Research Council (ERC) under the European Union's Horizon 2020 and Horizon Europe research and innovation program (Grant Agreement No. 802769, ERC Starting Grant “MapCat” and Grant Agreement No. 101077332, ERC Starting Grant “CC‐CHARGED”). I. B. acknowledges the Clore Israel Foundation, and the Harvey M. Krueger Family Center for Nanoscience and Nanotechnology for their financial support. L.L acknowledges Harvey M. Krueger Family Center for Nanoscience and Nanotechnology for their financial support. This project has received funding from the European Union's Horizon 2020 and Horizon Europe research and innovation program under grant agreement No. 101007417 and 101077332 having benefited from the access to OSMOS STM lab provided by CNR‐IOM in Trieste and by the Physics Department of the University of Milan for theoretical support, within the framework of the NFFA‐Europe Pilot Transnational Access Activity, proposal ID443. We acknowledge the CINECA award under the ISCRA initiative, for the availability of high performance computing resources and support.
© 2023 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.
- N-Heterocyclic Olefins
- Scanning Tunneling Microscopy
- Self-Assembled Monolayers
- Surface Chemistry
- X-Ray Absorption Spectroscopy