Infrared, Raman and resonance Raman investigations of methylviologen and its radical cation

Abstract

The infrared and Raman spectra of methylviologen (l,l'-dimethyL4,4'-bipyridine dication, MV") have been measured from both the solid dichloride and aqueous solutions. The preresonance behaviour of MV2+ Raman bands showed that the absorption at -196 nm is mainly responsible for the resonance scattering process in MV". In the region below 1700 cm-', nine polarized (p-113) resonance Raman bands of the methylviologen radical cation, MV", were assigned to in-plane ring modes. Arguments are given that the chromophore of MV+' may also partially include the methyl groups. The excitation profiles of the MV" fundamentals, measured with laser wavelengths covering the range 350.6-676.4 nm, reveal three main groups of modes, each behaving differently for the excitation in this range. Modes containing largely u(C-C) ring contributions are mainly coupled with electronic transitions at -395, -605 and -720 nm and yield simple excitation profiles. Modes involving principally the vibrations of the N+-CH, group show complicated interference peaks in the whole range of the excitation profiles. y(CCC) is mainly coupled with the absorption at -620 nm. Resonance Raman bands of the (MV"), dimer have been characterized through studies of the concentration dependence of the spectra.

A Vibrational Spectroscopic Study of the Structure of Electroactive Self-Assembled Monolayers of Viologen Derivatives

“…Figure 8 shows the structure of a generalized viologen derivative, along with an arbitrarily chosen axis system. The symmetry is taken to be D2h, implying a coplanar arrangement of the two rings, consistent with previous vibrational spectroscopic studies (2,(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32)) and x-ray crystal structures (33,34). From the body of work described above, there is general agreement that the band at 1169 cm" 1 is mainly derived from the Ag N-R stretch between the ring nitrogen and the first methylene group in the chain.…”

Surface-enhanced Raman Spectroscopy of Benzimidazolic Fungicides: Benzimidazole and Thiabendazole

“…These are attributed to totally ring stretching vibrations as also confirmed by comparison with assignments made for similar structural pesticides. 22,29 While, the strong bands of intensity appearing at 786, 1018 and 891 cm -1 in the SERS spectrum may be assigned to C-H out-of plane bending modes and C-C-S out-of-plane bending mode, respectively. The band frequencies and their assignments based on literature and calculation are given in Table 2.…”

Orientation and Organization of Langmuir−Blodgett Mixed Films Consisting of a Phospholipid and a Viologen Studied by Infrared Spectroscopy

“…This increase of the maximum intensity corresponding to the 1458 cm -1 mode for the mixed monolayer with respect to DMPA film could be attributed to the additional methyl group directly bound to the bipyridyl group (N + -CH 3 ) (Scheme 1). In fact, according to Hester et al, 28,29 the methyl viologen shows a (δ-CH 3 ) vibration mode at 1461-1440 cm -1 .…”

“…The assignment of these bands has been ascribed assuming a D 2h symmetry, 14,28,29,38,39 where the two rings of the bipyridyl group are coplanar. Thus, the 3017 cm -1 band may be attributed to the ring C-H stretching vibration, and the 1642 and 1304 cm -1 bands to B 2u and A g ring modes, respectively.…”