The characterization and controlled manipulation of molecules gives insight into fundamental physical and chemical processes, which are of central importance in nanoscience. In this talk, I will present several examples of functional molecules, which are studied and manipulated under ultrahigh vacuum conditions by scanning tunneling microscopy (STM) on the single-molecule level. This is important because it allows to control and investigate at the atomic-scale how the local environment affects the function of every single molecule.

By using the on-surface polymerization technique [1], molecular wires [2] or molecular nodes with different conjugation pathways [3] can be fabricated from specifically designed molecular building blocks. In the case of molecular switches, the switching rate can strongly depend on the direct environment of each molecule, resulting in

“switching patterns” [4]. Similar effectswere observed for porphycene molecules,where the presence (or absence) of onlyone atom in the surroundings of themolecule can alter intramolecular protontransfer [5]. Using the STM tip tomanipulate dipolar molecules, these canbe either precisely rotated [6] or displacedon a surface, also in a pseudo-blind (andtherefore much faster) mode [7]. In thecase of fluorene derivatives, singlemolecules can be moved with highprecision over large distances, evenbetween two independent STM tips (seeFigure) [8], allowing to determine travelingdistance and time for a single molecule.Molecular motors are fascinating objects that can convert energy into controlled, directional motion. A novel type of ‘adsorbate motor’ will be presented, which is based on a simple molecule that does not contain any motor function [9]. Instead, it achieves this functionality only in combination with a surface. These nanomachines can also do work by transporting single CO molecules as ‘cargo’ from one place to another.

[1] L. Grill et al., Nature Chem. 12, 115 (2020); [2] C. Nacci et al., Nature Comm. 6, 7397 (2015); [3] C. Nacci et al., Angew. Chem. Int. Ed. 55, 13724 (2016); [4] C. Dri et al., Nature Nanotech. 3, 649 (2008); [5] T. Kumagai et al., Nature Chem. 6, 41 (2014); [6] G. J. Simpson et al., Nature Comm. 10, 4631 (2019); [7] G. J. Simpson et al., Nature Nanotech. 12, 604 (2017); [8] D. Civita et al., Science 370, 957 (2020); [9] G. J. Simpson et al., Nature 621, 82 (2023)