Thiophene Derivatives on Gold and Molecular Dissociation Processes

Abstract

We report a systematic study of thiophene derivatives on gold surfaces. These molecules are of interest in molecular electronics, and the characracteristics of the thiophene–electrode interface in devices needs to be understood as it affects electron transport characteristics. Some experiments indicated S–C bond scission in contact with metals resulting in disruption of the π-electron system that affects charge transport, which would also be affected by presence of split-off chemisorbed sulfur. We explored this dissociation aspect by photoemission for the case of monocrystalline Au(111) surfaces and Au films grown on mica for a series of polythiophenes molecules (nT, n = 1–4, 6) as well as for α,ω-diquaterthiophene (DH4T) and dihexylsexithiophene (DH6T). The S 2p X-ray photoelectron spectroscopy peaks are found to have complex line shapes corresponding to S atoms with different core level binding energies (CLBE). Density functional theory calculations of adsorption energies and CLBEs were performed for various adsorption configurations of thiophene on a perfect Au(111) plane and for comparison, calculations were also performed for bithiophene, terthiophene, alkenethiol, alkenethiol chain, and a broken thiophene related metallocycle, incorporating an Au adatom and an S atom. On the basis of these results we relate the different contributions to the S 2p peak to intact molecules on different adsorption sites and broken molecules. Calculations in particular show that the CLBEs for intact thiophene (1T) can be the same as for the alkene and alkanethiol cases as opposed to usual assumptions in the literature. The existence of intact thiophenes is confirmed by the presence of clear π resonance peaks in the near edge X-ray fine structure (NEXAFS) spectra. Spontaneous dissociation appears to a variable extent in different samples, and we tentatively relate this to the presence of a more or less large number of steps and defects sites. X-ray induced beam damage was investigated for 1T and 3T using an intense synchrotron beam of 260 eV photons, and showed changes in the S 2p spectra related to S–C bond scission.

An estimation on the mechanical stabilities of SAMs by low energy Ar+ cluster ion collision

“…1 d), although a small new component in the spectrum at 161.1 eV appears. This small energy component is related to thiolate-Au bond but at a second adsorption position 5 . Briefly, molecules form dense SAM due to non-bonding intermolecular interactions to provide minimum space packing between the molecules.…”

“…Depending on the molecular backbone, a different anchor angle between the sulfur and gold atom is realized, which further determines the orientation of the SAM arrays. X-ray photoemission measurements also reveal a binding energy shift with different bonding positions of thiol on Au (111) single crystal surface 5 . Studies on the effects of the substrate morphology on the adsorbed molecules have been conducted in terms of, molecular size, charge exchanging, electric dipolar modification, working function variation and electronic level alignment to the Fermi edge.…”

Inside Back Cover: Hemilabile Ligands as Mechanosensitive Electrode Contacts for Molecular Electronics (Angew. Chem. Int. Ed. 46/2019)

“…Thiophenes are known to interact with Au electrodes and have been successfully used as molecular termini in several single-entity electronics studies. [22][23][24][25][26][27][28] Thei nteraction is reported as being weaker than traditional contact groups, [29] consistent with the known coordination chemistry of thiophenes [30][31][32] and their established use in hemilabile ligand design, [33][34][35] thus making them an ideal "supporting" molecular contact to the stronger methyl thioether. Furthermore, there are reports in the literature of unusual properties of oligothiophene-based molecular wires,s howing non-monotonic conductance attenuation with length, [36][37][38] stretchinginduced conductance decrease, [38] and large spread of conductance values [39] (see the Supporting Information for further details).…”

Development of a thiophene derivative modified LDH coating for Mg alloy corrosion protection

“…The peak at 401.8 eV is attributed to the quaternary ammonium salt structure, and the latter is related to the thiophene ring of as-synthesized the NTA inhibitor (Figure 4b). Notably, the binding energy of S 2p for a thiophene ring should be centered at 163.9 eV [45,46], but an obvious positive chemical shift of 0.7 eV to 164. 6 eV is observed, as shown in Figure 4c.…”

“…The main component, located at 284.8 eV, is assigned to C-C/C=C bonds originating from both NTA and ubiquitous carbon from the air [47]. The second component located at 286.0 eV is ascribed to the C-N bond in the quaternary ammonium group of NTA [22], the third and fourth components at 286.3 and 288.7 eV are associated with C-S bonds in the thiophene ring of NTA and trace carbonyl group (C=O) from the underlying MgAl-LDH layer, respectively [44,45]. with Mg oxidation and the adsorption/desorption of corrosion products at vulnerable sites [52].…”