Modification of Electrode Surfaces by Self‐Assembled Monolayers of Thiol‐Terminated Oligo(Phenyleneethynylene)s

Abstract

The wire‐like properties of four S‐(4‐{2‐[4‐(2‐phenylethynyl)phenyl]ethynyl}phenyl) thioacetate derivatives, PhC≡CC6H4C≡CC6H4SAc (1), H2NC6H4C≡CC6H4C≡CC6H4SAc (2), PhC≡CC6H2(OMe)2C≡CC6H4SAc (3) and AcSC6H4C≡CC6H4C≡CC6H4SAc (4) (Figure 1), all of which possess a high degree of conjugation along the oligo(phenyleneethynylene) (OPE) backbone, were investigated as self‐assembled monolayers (SAMs) on gold and platinum electrodes by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The redox probe [Fe(CN)6]4− was used in both the CV and impedance experiments. The results indicate that the thiolates derived from thioacetate‐protected precursor molecules 1 and 2 form well‐ordered monolayers on a gold electrode, whereas SAMs derived from 3 and 4 exhibit randomly distributed pinholes. The electron tunnelling resistance and fractional coverage of SAMs of all four compounds were examined using electron tunnelling theory. The analysis of the results reveal that the well‐ordered SAMs of 1 and 2 exhibit higher charge‐transfer resistance in comparison to the defect‐ridden SAMs of 3 and 4. The additional steric bulk offered by the methoxy groups in 3 is likely to prevent efficient packing within the SAM, leading to a microelectrode behaviour, when assembled on a gold electrode surface. The protected dithiol derivative 4 probably binds to the surface through both terminal groups which prevents dense packing and leads to the formation of a monolayer with randomly distributed pinholes. Atomic force microscopy (AFM) was used to examine the morphology of the monolayers, and height images gave root‐mean‐square (RMS) roughness′s which are in agreement with the proposed SAM structures.

Substrate-Dependent Study of Chain Orientation and Order in Alkylphosphonic Acid Self-Assembled Monolayers for ALD Blocking

“…The data collected can be represented in a Bode phase plot. The technique has been used in previous studies to investigate the quality of SAMs on several surfaces. ,,− Here, the technique is used to evaluate the relative coverage of ODPA on Cu, Co, W, and Ru. A well-packed SAM typically fits the Helmholtz model of an ideal capacitor .…”

Effect of Ligand Charge on Electron-Transfer Rates of Water-Soluble Gold Nanoparticles

“…29 As a gold nanoparticle is a three-dimensional selfassembled monolayer (SAM), its electrochemical properties are similar to two-dimensional SAMs and the formation of gold oxide occurs through pinhole defects in the monolayer. 30,31 Typically, gold oxide easily forms at high pH. Despite this, the water-soluble AuNPs exhibit a decrease in electron transfer when at high pH.…”

“…While some work suggests that the ligand thiolate can be oxidized, other evidence suggests that, in this system, electron transfer occurs through gold oxide formation on the surface of the core of the nanoparticle (Supporting Information, Figures 3–5) as seen in unprotected nanoparticles . As a gold nanoparticle is a three-dimensional self-assembled monolayer (SAM), its electrochemical properties are similar to two-dimensional SAMs and the formation of gold oxide occurs through pinhole defects in the monolayer. , …”

Catalytic Activation of Trimethylsilylacetylenes: A One-Pot Route to Unsymmetrical Acetylenes and Heterocycles

“…Diaryl acetylenes are widely used compounds not only because of their synthetic utility but also because of their unique optical and electronic properties . In the art of molecular engineering diaryl acetylenes are often used as linear building blocks . Their synthesis therefore is a useful conquest of organic chemistry and has different solutions.…”