Umwandlung der absoluten Konfiguration einzelner Adsorbatkomplexe

Abstract

Chiralitätsumkehr durch Elektronen: Propenmoleküle bilden chirale Komplexe bei Adsorption auf einer Kupferoberfläche. Inelastisch gestreute Tunnelelektronen aus der Spitze eines Rastertunnelmikroskops regen molekulare Schwingungen an, die zur Rotation oder Diffusion des Adsorbats auf der Oberfläche führen. Bei höheren Tunnelströmen wird auch die Umwandlung in die entgegengesetzte Konfiguration beobachtet.

Oligo(naphthylene–ethynylene) Molecular Rods

“…Chirality can also result from the molecular conformation. However, the importance of conformational degrees of freedom for assembly of chiral structures has received only limited attention 9,10. In previous work we studied prochiral molecular rods formed from oligo(phenylene ethynylene)s terminated by two tert ‐butyl‐salicylaldehyde moieties 11,12.…”

Mode‐Selective Electrical Excitation of a Molecular Rotor

“…Therefore, for molecules to meet their full potential as components in molecular machines, methods for coupling them to external sources of energy that selectively excite the desired motions must be devised. [1,[5][6][7][8][9][10][11][12][13][14][15][16][17] Herein we describe a study of the electrical excitation of individual dibutyl sulfide (Bu 2 S) molecular rotors with electrons from a scanning tunneling microscope (STM) tip. Action spectroscopy was used to measure the effect of electron energy on the rate of rotation.…”

“…This technique correlates the occurrence of a molecular event such as internal rearrangement, translation, dissociation, or rotation to the energy of the electrons inducing the process. [5][6][7][8][9][10][11][12][13][14] Figure 2 a shows action spectra collected by placing the STM tip at the edge of a dibutyl sulfide molecular rotor with the feedback loop switched off such that the tip could both excite the molecule and monitor its rate of rotation by recording changes in the tunneling current. The rotation rate was measured as a function of sample bias at constant tunneling current and at temperatures less than 8 K so that no thermally-induced rotation occurred.…”

“…[6][7][8][9][10][11] Previous experiments have shown that this energy transfer can occur via anharmonic coupling of high-energy vibrational modes into lower energy rotational and frustrated translational modes. [6][7][8][9][10][11]13] It has even been demonstrated that molecular translation or desorption events can be selectively excited if the correct input energies are chosen. [8] These coupling efficiencies are dependant on both the type and the energy of all the vibrational and rotational modes of the molecule.…”

“…[6,8,11] As dibutyl sulfide contains 27 atoms, the details of how the coupling occurs is beyond the level of current theory, but the fact that C À H stretches can drive rotation suggests that the rate of relaxation via energy transfer to the surface is not fast enough to completely quench the observed rotation. [6,[8][9][10][11][12][13][14]23] It is therefore not surprising given the complex transfer of energy through different modes of the molecule that dibutyl sulfide and its deuterated counterpart have different coupling efficiencies. Overall, excitation of dibutyl sulfide (at 400 meV) and its deuterated counterpart (at 300 meV) gave 1 10 À6 and 5 10 À8 rotations per electron, respectively.…”