TY  - JOUR
AU  - Han, B.
AU  - Li, Z.
AU  - Wandlowski, Th.
AU  - Blaszcyk, A.
AU  - Mayor, M.
TI  - Potential-induced redox Switching in Viologen Self-assembled Monolayers - An ATR-SEIRAS Approach
JO  - The journal of physical chemistry  / C
VL  - 111
SN  - 1932-7447
CY  - Washington, DC
PB  - Soc.
M1  - PreJuSER-58667
SP  - 13855 - 13863
PY  - 2007
N1  - Record converted from VDB: 12.11.2012
AB  - 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.
KW  - J (WoSType)
LB  - PUB:(DE-HGF)16
UR  - <Go to ISI:>//WOS:000249501800032
DO  - DOI:10.1021/jp073208g
UR  - https://juser.fz-juelich.de/record/58667
ER  -