Can N-ethyl-N '-octadecyl viologen dimerize on octadecanethiol-coated goldelectrode?

Electrochcmical and ex situ FTIR spectral techniques have been used to stud y the insertion of asymmetric alkyl viologen, N-ethyl-N'-octadecyl viologen (C18EV2+) into the self-assembled monolayers (SAMs) of octadecanethiol (OD T) on Au electrode surface. in the IR reflection absorption (IRRA) spectros copic measurements, the relative magnitude of the -CH2- and CH3- stretching modes of ODT and their peak positions indicated that ODT forms a densely p acked crystalline-like assembly on polycrystalline Au electrode. Furthermor e, a considerable increase in the -CH2- stretching mode intensity relative to that of the CH3- stretching mode in the C18EV2+-insertcd ODT monolayer s uggested a greater disorder in the alkyl chains of the C18EV2+-intercalated ODT monolayer than in the pure ODT monolayer. In the cyclic voltammetry st udies, C18EV2+ showed a neat broad redox wave at low surface coverage of C1 8EV2+ on the ODT-coated electrode and a sharp reduction and multiple oxidat ion peaks at high surface coverage, The potential difference subtractively normalized interfacial FTIR (SNIFTlR) spectral studies showed that at high surface coverage of C18EV2+ inserted on the ODT-coated electrode, the elect rogenerated radical cations of C18EV2+ are close and in an ol icntation pro per enough to form the dimer; the spectral features characteristic of the d imer were observed. On the other hand, at similar surface coverage of C18EV 2+, such spectral features were not observed for the SAMs of C18EV2+ on bar e Au electrode because of the less ordered orientation of C18EV2+. (C) 2000 Elsevier Science Ltd. All rights reserved.