Transoid-to-Cisoid Conformation Changes of Single Molecules on Surfaces Triggered by Metal Coordination

Abstract

Conformational isomers are stereoisomers that can interconvert over low potential barriers by rotation around a single bond. However, such bond rotation is hampered by geometrical constraints when molecules are adsorbed on surfaces. Here, we show that the adsorption of 4,4′-bis(4-carboxyphenyl)-6,6′-dimethyl-2,2′-bipyridine molecules on surfaces leads to the appearance of prochiral single molecules on NiO(001) and to enantiopure supramolecular domains on Au(111) surfaces containing the transoid-molecule conformation. Upon additional Fe adatom deposition, molecules undergo a controlled interconversion from a transoid-to-cisoid conformation as a result of coordination of the Fe atoms to the 2,2′-bipyridine moieties. As confirmed by atomic force microscopy images and X-ray photoelectron spectroscopy measurements, the resulting molecular structures become irreversibly achiral.

Recent highlights in nanoscale and mesoscale friction

“…It is possible to resolve the internal structure of molecules, including their bond order [ 181 – 182 ]. In preliminary experiments [ 195 ], it was possible to observe the conformational changes of single adsorbed molecules due to the presence of single Fe atoms acting as catalytic centers ( Fig. 9 ).…”

Charge Displacement Analysis—A Tool to Theoretically Characterize the Charge Transfer Contribution of Halogen Bonds

“…Some years ago, Frenking and Krapp compared chemical bonds to unicorns [1], never-seen entities of which everybody talks. Actually, experimental techniques developed so much that in the last years it has been possible to obtain pictures of single molecules, as Atomic Force Microscopy [2][3][4][5]. But even if we are approaching to an experimental characterization of chemical bonds, theoretical bond analysis remains central to deeply understand the nature of chemical bonds in all its variations.…”

Comparing a porphyrin- and a coumarin-based dye adsorbed on NiO(001)

“…Atomically clean NiO surfaces, mandatory for reliable SPM studies, are difficult to prepare because of the hardness of the material and its high reactivity [12–15 26–34]. Fig.…”

“…Fig. 2 shows the frequency-shift signal acquired using the multipass imaging technique [14–15 35–36] clearly showing atomic resolution of the NiO(001) surface. Employing this method, the crystallographic directions of the substrate are resolved with atomic accuracy, and upon comparing them with the large-scale image, one can deduce that the step edges of NiO(001) as well as the observed defects run along the [110] direction (see violet dotted lines in Fig.…”

“…In contrast to TiO 2 [3–11], wide-bandgap p-type semiconductors, such as NiO, and their functionalization with sensitizers, have been less extensively studied by using SPM [12–15]. NiO was the first reported p-type wide-bandgap semiconductor [16], and can be used for the fabrication of p-type DSSCs with photoactive cathodes, a first step towards the design of tandem solar cells with two photoactive electrodes [17–18].…”