Electrochemical and in Situ FTIR Spectroscopic Investigation on the Electrochemical Transformation of 4-Aminothiophenol on a Gold Electrode in Neutral Solution

Abstract

The electrochemical transformation of the self-assembled monolayer of 4-aminothiophenol (4-ATP) has been studied in neutral solution by means of electrochemical and in situ FTIR measurements, and the results are compared with those in acidic solution. The electrochemical transformation in neutral solution results in the formation of a surface-confined aniline dimer, 4‘-mercapto-N-phenylquinone diimine as in the case of acidic solution. The redox peak corresponding to the aniline dimer shifts by −56 mV while increasing the solution pH by 1 unit, suggesting that protons and electrons take part in the redox reaction in the ratio of 1 to 1. The surface coverage of the aniline dimer obtained in the neutral solution is relatively low ((1.3 ± 0.3) × 10-10 mol cm-2) when compared to that in 0.1 M HClO4 solution ((2.4 ± 0.3) × 10-10 mol cm-2). Very similar in situ FTIR spectral features were obtained in both acidic and neutral solutions, indicating that the reaction mechanism follows the same head-to-tail coupling in neutral solution as in the case of acidic solution. The electrochemical and FTIR spectroscopic studies of the model compound, N-phenyl-1,4-phenylene diamine, support the formation of aniline dimer on the electrode surface during the electrochemical transformation of 4-ATP in neutral and acidic solutions. The electroproduced diimine undergoes hydrolysis to yield the monoimine while holding the electrode at high positive potential.

Spectroelectrochemical behavior of 4-aminobenzenethiol on nanostructured platinum and silver electrodes

“…Among them, SAMs based on aromatic thiols have been vastly studied [13,14]. The formation of organic monolayers by self-assembly is directed by a specific interaction between a terminal functional group and the surface, in this case, the bond formed between the thiol sulphur and the metal.…”

Electrochemical Studies of Chemically Modified Nanometer‐Sized Electrodes

“…The height of peak A and B decreases and the height of peak C increases with the pH value of the solution increase [22]. Contradictory information could be found in References, for example [22] mentioned peak B and C could disappear at solution pH > 6 while [24] said both Peak B and C could be observed even when solution pH > 9. In our experiment, we could only observe peak C (see Figure 2).…”

“…Although the extent of decrease in limiting current is different for different 4-ATP SAMs modified nanometer-sized Au electrode, the phenomenon is reproducible. According to References [22][23][24], 4-ATP molecules on the electrode are electrochemically dimerized to form 4'-mercapto-N-phenylquinone diimine (NPQD). It seems that the entire electrode is covered by NPQD molecules because the current of the oxidation of hydrazine on the modified electrode, which is believed to be an inner-sphere electron transfer reaction [28], is very small compared with the same reaction on the electrode before modification (see Figure 3c).…”

“…So, the decrease in current cannot be totally ascribed to the decrease in rate constant. From the structure and length of NPQD and 4-ATP [22][23][24], one can anticipate that 4-ATP molecules orient normal to the electrode and NPQD molecules either orient at an angle from the electrode or just disorderly cover the electrode. Since electron tunneling can only accomplished from the head group of 4-ATP or NPQD (=NH 2 + ) rather than from the side of the molecules, this means that the effective electrode area is decreased after the 4-ATP SAMs has been transformed into NPQDs.…”

Modification of electrodes with nanostructured functionalized thiadiazole polymer film and its application to the determination of ascorbic acid

“…This observation suggested that the electron transfer rate of the p-ATD film decreases when the deposition cycles increase. We calculated the surface coverage of the polymer film by integrating the area under the anodic wave [29]. A surface coverage of 2.12 × 10 −10 mol cm −2 was obtained for the p-ATD film deposited by 15 cycles.…”