%0 Journal Article
%A Han, B.
%A Li, Z.
%A Wandlowski, Th.
%A Blaszcyk, A.
%A Mayor, M.
%T Potential-induced redox Switching in Viologen Self-assembled Monolayers - An ATR-SEIRAS Approach
%J The journal of physical chemistry  / C
%V 111
%@ 1932-7447
%C Washington, DC
%I Soc.
%M PreJuSER-58667
%P 13855 - 13863
%D 2007
%Z Record converted from VDB: 12.11.2012
%X 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.
%K J (WoSType)
%F PUB:(DE-HGF)16
%9 Journal Article
%U <Go to ISI:>//WOS:000249501800032
%R 10.1021/jp073208g
%U https://juser.fz-juelich.de/record/58667