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| Home > Publications database > Potential-induced redox Switching in Viologen Self-assembled Monolayers - An ATR-SEIRAS Approach |
| Journal Article | PreJuSER-58667 |
; ; ; ;
2007
Soc.
Washington, DC
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Please use a persistent id in citations: doi:10.1021/jp073208g
Abstract: Monolayers of viologens (N-alkyl-N'-(n-thioalkyl)-4,4'-bipyridinium bromide, n = 6, 8, 10) have been self-assembled 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, V2+ <-> V center dot+, is reversible, whereas the second redox process, V center dot+ <-> V-0, is quasi reversible. The V2+ 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 V2+ is stabilized by interplanar pi-pi stacking and electrostatic coulomb interactions. Both monomers and dimers of V center dot+ coexist in the V center dot+ adlayer. The molecular alignment of the V center dot+ adlayer is stabilized by the strong vibronic coupling within the dimers and the pi-pi 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 center dot+ within the SAMs. The complex reaction, V2+ - V center dot+, is described as electron transport from the electrode to the V2+ moiety followed by the dimerization of V center dot+, the delocalization of the radical electrons, and the migration of coadsorbed ClO4- anions.
Keyword(s): J
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