Potential-Induced Redox Switching in Viologen Self-Assembled Monolayers: An ATR−SEIRAS Approach

Abstract

Monolayers of viologens (N-alkyl-N′-(n-thioalkyl)-4,4′-bipyridinium bromide, n ) 6, 8, 10) have been selfassembled from ethanolic solution onto gold substrates. Their structure and redox functionality were studied by cyclic voltammetry and in situ ATR-SEIRAS. Voltammetric experiments revealed that the first redox process, V 2+ T V •+ , is reversible, whereas the second redox process, V •+ T V 0 , is quasi reversible. The V 2+ adlayer exhibits a sandwich-like structure. Van der Waals interactions between the alkyl chains lead to two well-ordered hydrophobic layers, with the redox-active bipyridinium unit enclosed in between. The alkyl chains are aligned in an all-trans configuration in a tilted orientation with respect to the surface normal and exhibit a slight conformational disorder. The long axis of the central bipyridinium rings is also tilted. The alignment of V 2+ is stabilized by interplanar π-π stacking and electrostatic coulomb interactions. Both monomers and dimers of V •+ coexist in the V •+ adlayer. The molecular alignment of the V •+ adlayer is stabilized by the strong vibronic coupling within the dimers and the π-π stacking between the monomers. Increasing length of the alkyl chain results in more tilted bipyridinium units, and favors both the dimerization and the alignment of V •+ within the SAMs. The complex reaction, V 2+ f V •+ , is described as electron transport from the electrode to the V 2+ moiety followed by the dimerization of V •+ , the delocalization of the radical electrons, and the migration of coadsorbed ClO 4anions.

Electrochemical Control of Bioluminescence by Blocking the Adsorption of the Bacterial Luciferase Using a Mercaptobipyridine Self-assembled Monolayer

“…The redox behaviors of similar bipyridinium SAM modified electrodes have been reported. 11,14 Although the bipyridinium thiol having a different alkyl chain length of the terminal group was used in the previous study, the redox peaks obtained in the present study were similar to those of the previous one 11 (-0.31 V, corrected for Ag/AgCl electrode). In the literature, 11 the redox peaks correspond to the one-electron reduction of a bipyridinium unit shown in Eq.…”

Interfacial redox centers as origin of color switching in organic electrochromic device

“…Viologen is an organic compound for potential use in flexible electrochromic devices due to its activity in reversible redox reaction and excelent electron accepting nature. In other words, Viologens [9], [11][12][13][14] are reducible materials used in solid-state electrochromic devices, which may undergo one-or two-electron reductions. [9], [11][12][13][14] Ease of processing and use have stimulated intensive research into the electrochromic properties of viologens.…”

Spectroelectrochemical evidence of the role of viologen moiety as an electron transfer mediator from ITO substrate to a Pt complex acting as a confined molecular catalyst for hydrogen evolution reaction

“…While the absorbance at 600 nm started to decrease, that at 400 nm further increased as cathodic current of the second cathodic peak started to flow. Electrochemistry of viologen has been studied for long time [17][18][19][20] and it is well known that viologen dication (V 2+ ) is subject to the two step electrochemical reduction to yield the neutral form of viologen, V 0 , via radical cation form of viologen,…”