Detecting Mechanochemical Atropisomerization within an STM Break Junction

Zotti²,

Miguel

et al. 2018

J. Phys. Chem. C

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Using the break junction (BJ) technique we show that 'Au(RS)2' units play a significant role in thiol-terminated molecular junctions formed on gold. We have studied a range of thiol-terminated compounds, either with the sulfur atoms in direct conjugation with a phenyl core, or bonded to saturated methylene groups. For all molecules we observe at least two distinct groups of conductance plateaus. By a careful analysis of the length behavior of these plateaus, comparing the behavior across the different cores and with methyl sulfide anchor groups, we demonstrate that the lower conductance groups correspond to the incorporation of Au(RS)2 oligomeric units at the contacts. These structural motifs are found on the surface of gold nanoparticles but they have not before been shown to exist in molecular-break junctions. The results, while exemplifying the complex nature of thiol chemistry on gold, moreover clarify the conductance of 1,4-benzenedithiol on gold. We show that true Au-S-Ph-S-Au junctions have a relatively narrow conductance distribution, centered at a conductance of log(G/G0) = -1.7 (± 0.4).

Section: Break Junction Resultssupporting

confidence: 87%

The Role of Oligomeric Gold–Thiolate Units in Single-Molecule Junctions of Thiol-Anchored Molecules

Zotti²,

Miguel

et al. 2018

J. Phys. Chem. C

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“…Thep ercentage of junctions giving ap lateau for each compound is given in the caption to Figure 3( and in Table S1). [17] This analysis procedure ensures that the conductance values can be attributed to fully stretched singlemolecule junctions.I ta lso results in good overlap between histograms (of the same compound) from periods of measurement giving different percentages of molecular junctions. The molecular conductances plotted in Figure 3g and listed in Table 1a re quoted from the histograms in Figure 3f,w here we have considered only points from the end of the distribution, greater than the median length determined from aG aussian fit (see the Supporting Information for details).…”

mentioning

confidence: 99%

“…We had previously validated this method for afamily of porphyrins. [17] This analysis procedure ensures that the conductance values can be attributed to fully stretched singlemolecule junctions.I ta lso results in good overlap between histograms (of the same compound) from periods of measurement giving different percentages of molecular junctions. We often observed an apparent increase in the molecular conductance when the percentage of molecular junctions exceeded about 40 %, which was attributed to the formation of junctions containing several wired molecules.…”

mentioning

confidence: 99%

Unusual Length Dependence of the Conductance in Cumulene Molecular Wires

Hou

et al. 2019

Angew Chem Int Ed

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Cumulenes are sometimes described as “metallic” because an infinitely long cumulene would have the band structure of a metal. Herein, we report the single‐molecule conductance of a series of cumulenes and cumulene analogues, where the number of consecutive C=C bonds in the core is n =1, 2, 3, and 5. The [ n ]cumulenes with n =3 and 5 have almost the same conductance, and they are both more conductive than the alkene ( n =1). This is remarkable because molecular conductance normally falls exponentially with length. The conductance of the allene ( n =2) is much lower, because of its twisted geometry. Computational simulations predict a similar trend to the experimental results and indicate that the low conductance of the allene is a general feature of [ n ]cumulenes where n is even. The lack of length dependence in the conductance of [3] and [5]cumulenes is attributed to the strong decrease in the HOMO–LUMO gap with increasing length.

“…[a] Experimental conductance peak positions from data in Figure f; the run‐to‐run variation in peak position is about 0.02, see Figure S19. [b] The lengths were calibrated by adding 0.4 nm to the peak position of a Gaussian fit to the total distribution of plateau lengths . Values in parentheses are derived from the 95th percentile.…”

Section: Figurementioning

confidence: 99%

Unusual Length Dependence of the Conductance in Cumulene Molecular Wires

Hou

et al. 2019

Angewandte Chemie

Self Cite

Cumulenes are sometimes described as “metallic” because an infinitely long cumulene would have the band structure of a metal. Herein, we report the single‐molecule conductance of a series of cumulenes and cumulene analogues, where the number of consecutive C=C bonds in the core is n=1, 2, 3, and 5. The [n]cumulenes with n=3 and 5 have almost the same conductance, and they are both more conductive than the alkene (n=1). This is remarkable because molecular conductance normally falls exponentially with length. The conductance of the allene (n=2) is much lower, because of its twisted geometry. Computational simulations predict a similar trend to the experimental results and indicate that the low conductance of the allene is a general feature of [n]cumulenes where n is even. The lack of length dependence in the conductance of [3] and [5]cumulenes is attributed to the strong decrease in the HOMO–LUMO gap with increasing length.