Tripodal Binding Units for Self-Assembled Monolayers on Gold: A Comparison of Thiol and Thioether Headgroups

Abstract

Whereas thiols and thioethers are frequently used as binding units of oligodentate precursor molecules to fabricate self-assembled monolayers (SAMs) on coinage metal and semiconductor surfaces, their use for tridentate bonding configuration is still questionable. Against this background, novel tridentate thiol ligands, PhSi(CH2SH)3 (PTT) and p-Ph-C6H4Si(CH2SH)3 (BPTT), were synthesized and used as tripodal adsorbate molecules for the fabrication of SAMs on Au(111). These SAMs were characterized by X-ray photoelectron spectroscopy (XPS) and near edge X-ray absorption fine structure (NEXAFS) spectroscopy. The PTT and BPTT films were compared with the analogous systems comprised of same tripodal ligands with thioether instead of thiol binding units (anchors). XPS and NEXAFS data suggest that the binding uniformity, packing density, and molecular alignment of the thiol-based ligands in the respective SAMs is superior to their thioether counterparts. In addition, the thiol-based films showed significantly lower levels of contamination. Significantly, the quality of the PTT SAMs on Au(111) was found to be even higher than that of the films formed from the respective monodentate counterpart, benzenethiol. The results obtained allow for making some general conclusions on the specific character of molecular self-assembly in the case of tridentate ligands.

Adsorption phenomena of cubane-type tetranuclear Ni(II) complexes with neutral, thioether-functionalized ligands on Au(111)

“…Since the binding of the {Ni 4 } to the surface is expected to be solely Table 1 and agree well with previous literature reports on thioether-functionalized molecules [20].…”

“…The doublet at 163.1 eV, which is responsible for 52.9% of the total signal, is attributed [20] to a weak coordination-type bond, which is the expected binding for a thioether group. The doublets at 162.1 and 161.1 eV have basically the same intensity and are responsible for the remaining 47.1% of the signal.…”

“…The 161.1 eV peak is either due to atomic sulfur or due to a thiol group with different binding chemistry [20,22] [20].…”

Thiocyanate Anchors for Salt-like Iron(II) Complexes on Au(111): Promises and Caveats

“…While atomic sulphur has been suggested [63], this is rather unlikely under the preparation conditions used here, and the alter- native interpretation of a different bonding configuration of thiolate is favoured [57 -60, 62]. Interestingly, in some studies this signal appears only in the initial stages of thiol adsorption [58,60], when the monolayer is still incomplete. This is consistent with the STM observation that the films are rather disordered and not densely packed.…”

Asymmetric Thioethers as Building Blocks for Chiral Monolayers

“…For example, the most common type of SAM involves thiol species (HSR) and utilizes a strong sulfurmetal interaction to form the layers [21][22][23][24][25]. Thiols can be functionalized with groups that are polar, aromatic, etc.…”