Influence of Thiol Molecular Backbone Structure on the Formation and Reductive Desorption of Self-Assembled Aromatic and Alicyclic Thiol Monolayers on Au(111) Surface

Abstract

The surface structure and electrochemical behavior of self-assembled monolayers (SAMs) prepared from benzenethiol (BT), cyclohexanethiol (CHT), and cyclopentanethiol (CPT) on Au(111) surface were examined by scanning tunneling microscopy (STM) and cyclic voltammetry (CV) to understand the influence of thiol molecular backbone structure on the formation and reductive desorption behavior of SAMs. STM imaging showed that BT and CPT SAMs on Au(111) surface formed at room temperature were mainly composed of disordered domains, whereas CHT SAMs were composed of well-ordered domains with three orientations. From these STM results, we suggest that molecule-substrate interaction is a key parameter for determining the structural order and disorder of simple aromatic and alicyclic thiol SAMs on Au(111). In addition, the reductive desorption peak potential for BT SAMs with aromatic rings was observed at a less negative potential of -566 mV compared to CHT SAMs (-779 mV) or CPT SAMs (-775 mV) with aliphatic cyclic rings. This reductive desorption behavior for BT SAMs is due to the presence of p-orbitals on the aromatic rings, which promote facile electron transfer from the Au electrode to BT as compared to CHT and CPT. We also confirmed that the reductive desorption behavior for simple alicyclic thiol SAMs such as CHT and CPT SAMs on Au electrodes was not significantly influenced by the degree of structural order.

The electrochemical stability of thiols on gold surfaces

“…The simple behavior observed for the reductive desorption of alkanethiol SAMs becomes more complex when aromatic or heterocyclic thiols are included in the same analysis since they have different S-Au bond strength [29], intermolecular forces dominated by π-π interactions, different surface coverage, and accordingly different surface structures [30]. In general they exhibit more positive E p values than those found for alkanethiol SAMs, a fact that has been associated with the aryl group that withdraws electrons from the Au surface easier than the aliphatic chains, thus favoring reductive desorption [31].…”

“…In this sense, there are two experimental characteristics that are important to consider. First the aromatic thiols have smaller θ values than the aliphatic ones (Table 1), and it is known from STM data that they form more disordered SAMs [31]. On the other hand, it has been shown that the structural order of aromatic thiol SAMs on Au(111) can be considerably enhanced by increasing the number of phenyl rings in the molecular backbone [66][67][68] and by inserting the alkyl spacer between the phenyl ring and the sulfur…”

A new variable temperature solution-solid interface scanning tunneling microscope

“…It is even possible to exercise electrochemical control over the formation of adlayers at SS interface. 16 The repair of defects in self-assembled layers at the SS interface can be promoted if there is a dynamic exchange between molecules on the surface and in the solution phase. 8,17 Different areas of technology and science profit from temperature dependent SS interface studies.…”

Molecular Self‐Assembly of Phenylselenyl Chloride on a Au(111) Surface

“…Cyclic voltammetry blocking experiments provide meaningful information regarding the electron-transfer properties of SAMs, which are significantly influenced by the formation and surface structural characteristics of monolayers. [35][36][37][38][39] Figure 2 displays cyclic voltammograms of bare Au and PSC SAM-covered Au electrodes. The PSC SAM-covered Au electrodes were obtained by soaking the Au electrode in a 0.01 mM ethanolic solution of PSC at 323 K for 2 h. The peak currents was 22.0 μA for the bare Au electrode and 13.8 μA for the PSC SAM-covered Au electrode.…”