Resonance Raman spectra of the N,N ‐ dihydro‐4,4′‐bipyridinium radical cation

Abstract

The Raman spectrum of diprotonated 4,4'-bipyridine in the solid state as the dibromide salt is reported. The resonance Raman spectrum of the radical cation derived by one-electron reduction of the dication is also reported. Viscous glycerol was employed as a solvent in order to protect the radical by inhibiting oxygen diffusion. The spectra are interpreted on the basis of a comparison with those of related compounds. A large shift in frequency (+70 cm-I) of the inter-ring stretching vibration between the parent dication and radical monocation is observed. This has been interpreted in terms of a major contribution to the delocalized radical structure of a quinoid-type form.

Controlled Photoinduced Generation of “Visual” Partially and Fully Charge Separated States in Viologen Analogues

“…In contrast, the strength of inter-ring C–C stretching at 1287 cm –1 and ring stretching at 1610 cm –1 for bipy decreased . This change is ascribed to the formation of a quinone structure and the decrease in the aromaticity of bipy and is similar to those observed in reported viologen compounds. , For 2 (Figure b), the vibrational change of the FCS state in comparison to the initial state is similar to the case for 1 . However, for the PCS state in comparison to the initial state, a significant increase in intensity for inter-ring C–C stretching at 1292 cm –1 and a minor enhancement of ring stretching at 1613 cm –1 were observed for bipy, while there was almost no change of intensity for the C–C stretching of carboxylate at 848 cm –1 .…”

“…Excitation wavelengths: λ ex (Zn-IBA) = 532 nm; λ ex ( 1 , 2 and Zn­(OAc) 2 ) = 785 nm. All comparisons are based on the band at 1018 ( 1 )/1016 ( 2 ) cm –1 , which is mainly attributed to a ring-breathing mode and partially to an in-plane C–H deformation of bipy . Assignment: 1287/1292 cm –1 , inter-ring C–C stretching of bipy; 1610 ( 1 )/1613 ( 2 ) cm –1 , ring stretching of bipy; 931 ( 1 )/848 ( 2 ) cm –1 , C–C stretching of carboxylate. , …”

Electronic Distribution in the Metal-to-Ligand Charge Transfer (MLCT) Excited States of [(4,4‘-(X)2bpy)(CO)3ReI(4,4‘-bpy)ReI(CO)3(4,4‘-(X)2bpy)]2+(X = H, CH3). Application of Time-Resolved Infrared and Resonance Raman Spectroscopies

“…In the TR 3 spectrum (354.7 nm excitation and scattering, in acetonitrile at 298 K), bands for 4,4‘-bpy* (* denotes excited state) 7 appear at 1024, 1242, 1358, 1508, and 1625 cm -1 . (Analogous bands are observed in the RR spectrum of the 4,4‘-bpy radical anion 7a.…”

“…Raman. In the resonance Raman (RR) spectrum of [(dmb)(CO) 3 Re(4,4‘-bpy)Re(CO) 3 (dmb)] 2+ (406.7 nm excitation, in acetonitrile at 298 K; dmb = 4,4‘-(CH 3 ) 2 bpy) 4,4‘-bpy bands appear at 1029, 1070, 1233, 1301, and 1621 cm -1 . Low-intensity dmb bands are also observed at 1495 and 1555 cm -1 …”

Colourimetric Carboxylate Anion Sensors Derived from Viologen‐Based Receptors

“…The viologen radical cation can also be probed by using resonance Raman spectroscopy. [44][45][46][47] Figure 21 shows the resonance Raman spectrum of the MV·PF 6 radical cation, measured with a 633 nm He-Ne laser. The peaks correspond to those reported in the literature.…”