A Molecular Approach to Self‐Assembly of Trimethylsilylacetylene Derivatives on Gold

Abstract

We recently discovered that a linear multifunctional trimethylsilylacetylene (TMSA) compound forms long-range and highly stable self-assembled monolayers (SAMs) on reconstructed Au(111). To better understand the interactions governing self-assembly in this new system, we synthesized a series of homologue organosilanes and performed scanning tunneling microscopy (STM) measurements at the Au(111)/n-tetradecane interface. The four TMSA-terminated linear silanes that we synthesized self-assemble in similar ways on gold, with the molecules standing upright on the surface. In contrast, compounds with a slightly modified terminal group but the same polyunsaturated linear chain above the TMSA head do not self-assemble. In particular, substituting a methyl group of TMSA with a more bulky one prevents self-assembly. Removing the C triple bond C triple bond of TMSA or substituting the Si atom by a C atom also hinders self-assembly. Finally, substituting one methyl group of TMSA by a hydrogen atom induces self-assembly but in a different geometry, with the molecules lying flat on the gold surface in a quasi-epitaxy mode. Our molecular approach demonstrates the key role played by the TMSA head in self-assembly, its origin being twofold: 1) the TMSA layers are commensurate to the Au(111) adlattice along the <112> direction, and 2) the C triple bond C triple bond of TMSA activates the Si atom and induces the creation of a surface Si-Au chemical bond. The highly stable TMSA-based SAMs appear then as promising materials for applications in surface modification.

Insulated molecular wires: inhibiting orthogonal contacts in metal complex based molecular junctions

“…As noted above, the trimethylsilylethynyl molecule-gold contact has been studied in a number of contexts, [91][92][93][94][95][96] and is well described in terms of physisorption of the methyl groups, augmented by a degree of charge transfer when residing near to surface defects. 14,67 It is only these latter situations that give rise to CuCSiMe 3 -contacted junctions of sufficient conductance to be measured.…”

“…The trimethylsilylethynyl group (CuCSiMe 3 ) has been shown to be a useful anchor in the construction of self-assembled monolayers (SAMs) of unsaturated hydrocarbons on gold, with the electron-withdrawing ethynyl moiety playing an essential role in stabilizing the gold-molecule interaction. [91][92][93][94] As a contacting group in molecular junctions, the CuCSiMe 3 moiety is known to favor only a single, albeit low conductance, contact. 14,[95][96][97] This is due to the fact that the CuCSiMe 3 group makes effective electrical contact to defect sites on the gold electrode surfaces in a restricted range of geometries, limited in part due to the steric bulk of the ancillary methyl groups.…”

Single-Molecule Electronics: Chemical and Analytical Perspectives

“…It has also been shown to be possible to form junctions with terminal trimethylsilylethynyl (TMSE, -C≡C-SiMe 3 ) and gold electrodes (75)(76)(77). Trimethylsilylethynyl had been previously shown to be a contacting group for forming stable SAMs on Au (110,(78)(79)(80)(81). In the case of molecular electrical junctions, TMSE was promoted as an anchoring group for simplifying the conductance histograms, given a single low conductance peak was seen rather than the multiple or broad conductance features observed for other anchoring groups such as thiols and pyridyl end groups.…”

Conductance Mechanism in a Linear Non-Conjugated Trimethylsilyl-Acetylene Molecule: Tunneling Through Localized States

“…It belongs to the family of polyunsaturated linear trimethylsilyl-acetylenes (TMSA: -C≡C-Si(CH 3 ) 3 ), that we have discovered as forming self-assembled monolayers (SAMs) by grafting on Au(111) [30,31]. These TMSA molecules spontaneously adsorb on gold in an upright position, the silicon atom being close to the surface and inducing the creation of a surface Si-Au chemical bond [32,33]. The high stability of TMSA-based SAMs allows to carry out scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS).…”