Hydrophilicity and Microsolvation of an Organic Molecule Resolved on the Sub‐molecular Level by Scanning Tunneling Microscopy

Abstract

Low-temperature scanning tunneling microscopy was used to follow the formation of a solvation shell around an adsorbed functionalized azo dye from the attachment of the first water molecule to a fully solvated molecule. Specific functional groups bind initially one water molecule each, which act as anchor points for additional water molecules. Further water attachment occurs in areas close to these functional groups even when the functional groups themselves are already saturated. In contrast, water molecules surround the hydrophobic parts of the molecule only when the two-dimensional solvation shell closes around them. This study thus traces hydrophilic and hydrophobic properties of an organic molecule down to a sub-molecular length scale.

Imaging the Solvation of a One‐Dimensional Solid on the Molecular Scale

“…Thea ggregation of water molecules at the chain ends thus represents the formation of ah ydration shell as already seen in Ref. [14]. Thee xact attachment sites of the water molecules at the chains were again identified with am odified tip (Figure 2b).…”

“…[27] Indeed, for functionalized azobenzenes, which possess similar aromatic hydrogen atoms,w ater molecules did not attach at these positions under comparable experimental conditions. [14,15] In contrast to the single hydrogen atoms available for binding in Refs. [14] and [15],MDAF and the chains offer positions where aw ater molecule might attractively interact with more than one hydrogen atom;these are indeed the adsorption positions revealed by as uperposition of the STM image and gas-phase structures of MDAF molecules (Figure 2c).…”

“…[14,15] In contrast to the single hydrogen atoms available for binding in Refs. [14] and [15],MDAF and the chains offer positions where aw ater molecule might attractively interact with more than one hydrogen atom;these are indeed the adsorption positions revealed by as uperposition of the STM image and gas-phase structures of MDAF molecules (Figure 2c). Theo bserved attachment sites are either located at the hydrogen atoms of the C4 and C5 carbon atoms or close to the C1 carbon atom and the diazo group.…”

“…[10][11][12][13] However,a st hese experiments are conducted mostly under ambient conditions,t he interactions of individual solvent molecules with the solid are not traceable owing to intrinsic thermal fluctuations.Low-temperature scanning tunneling microscopy (STM) eliminates the thermal motion of molecules and offers the required spatial resolution. [14,15] Here,weused this technique to follow the solvation of ah ydrogen-bonded solid in real space.T he hydrogenbond-assisted formation of supramolecular networks on surfaces has been thoroughly investigated by scanning probe microscopic techniques in recent years. [16][17][18][19][20][21] These networks may be understood as low-dimensional crystals,which makes them excellent test subjects for the investigation of solvation processes by STM.…”

Imaging the Solvation of a One‐Dimensional Solid on the Molecular Scale

“…However, as these experiments are conducted mostly under ambient conditions, the interactions of individual solvent molecules with the solid are not traceable owing to intrinsic thermal fluctuations. Low‐temperature scanning tunneling microscopy (STM) eliminates the thermal motion of molecules and offers the required spatial resolution . Here, we used this technique to follow the solvation of a hydrogen‐bonded solid in real space.…”