Reversible redox of 2,5-dihydroxythiophenol chemisorbed on gold and platinum electrodes: evidence for substrate-mediated adsorbate-adsorbate interactions

Abstract

The reversible quinone/diphenol redox of 2,5-dihydroxythiophenol (DHTP) chemisorbed on smooth polycrystalline platinum and gold electrodes has been studied by thin-layer electrochemistry. The packing density and mode of binding (through the SH moiety) of the subject compound were found to be identical on both surfaces. However, the width of the redox peak of the pendant diphenolic group, an indicator of intermolecular quinone-diphenol interactions, is at least twice as large on Pt as it is on Au. In the absence of the SH moiety, hydroquinone itself is irreversibly adsorbed on platinum but not on gold. These results suggest that the adsorbate-adsorbate interactions occurring on Pt are principally substrate mediated.

Synthesis and electrochemistry of self-assembled monolayers containing quinone derivatives with varying electronic conjugation

“…Given that the proton-coupled ET reactions displayed in quinones (Q/H 2 Q) are common in biology [8], they have been extensively studied at electrode surfaces [9][10][11][12]. Since the initial electrochemical studies of the hydroquinone/quinone redox centers contained in SAMs [9,13], the role of electron tunneling in bridging groups along with pH effects have also been explored [10,14,15]. The stepwise ET mechanism of a surface confined 2-electron, 2-proton couple was theoretically treated by Laviron by means of a nine member square-scheme, assuming that protonation is at equilibrium [16].…”

Electrochemical Behavior of Azobenzene Self-Assembled Monolayers on Gold

“…They generally exhibit ideal reversible surface waves. Also available are some reports concerning quinone SAMs fabricated by both self-assembly of thiol-functionalized quinone derivatives [11][12][13] and step-by-step surface reaction. [14][15][16][17] However, little work has been performed on azobenzene/hydrazobenzene redox couples.…”

“…They generally exhibit ideal reversible surface waves. Also available are some reports concerning quinone SAMs fabricated by both self-assembly of thiol-functionalized quinone derivatives − and step-by-step surface reaction. − However, little work has been performed on azobenzene/hydrazobenzene redox couples. − The electrochemical behavior of azobenzene and its derivatives in solution has been studied extensively because of the involvement of proton transport, adsorption/desorption, and cis/trans isomerization. − The electrochemical behavior of azobenzene Langmuir−Blodgett films has been intensively studied in our group. − We are currently trying to introduce azobenzene functionality into self-assembled monolayers in order to investigate their voltammetric properties.…”

Chemisorption and Electrochemical Activity of Thiophenols at Well-Defined Pd(111) Surfaces: Studies by LEED, AES, HREELS, and Electrochemistry

“…3,11,13 It was further found out that: (a) peak broadening is induced by attractive interactions between adsorbed molecules; 16,17 (b) such attractive forces are similar to those in the quinhydrone (1:1 Q:H2Q) complex and favor the formation of a 1:1 Q-to-H2Q ratio within the chemisorbed DHT layer; 18 (c) the full width at half maximum (FWHM) of DHT on Pt (0.21 V) is much larger than that on Au (0.13 V) due to a stronger affinity of the diphenolic moiety to the Pt surface relative to the Au surface; (d) when a -CH2-group, which does not possess delocalized electrons, is inserted between the diphenolic ring and the -SH group, as in the case of 2,5-dihydroxy-4-methylbenzenemercaptan (DHBM), the peak broadening effect disappeared on Pt. 2,11,13,19,20 Based on these results, it was postulated that the adsorbateadsorbate interaction that led to the redox peak broadening occurred through the substrate and not through space; no such substrate-mediated interaction occurred on Au because the aromatic ring is inert towards it.…”