Spectres Raman de Résonance de Dérivés Parasubstitués de l' Azobenzène

Abstract

Resonance Raman spectra of twenty parasubstituted azobenzene derivatives are compared, enabling a more complete assignment of bands to be made. Since all the spectra are rather similar, the various ring substituents are not resonance Raman active, and all the observed bands can be assigned to vibrational modes of the aromatic rings and to the azo group itself. Frequency shifts in the PhN stretching region are opposite to those expected based on delocalization along the PhNNPh moiety. From the complexity of band pattern around the NN stretching region and from the above described frequency shifts, several types of vibrational coupling are evident. On the basis of the band assignments, some useful conclusions can be reached for interpreting the observed spectral changes when azobenzene derivatives are used as chromophore probes in biochemical system studies.

Vibrational analysis of [4-[(E)-phenylazo] phenyl]ethanol based on the comparison between the experimental and DFT calculated Raman spectra

“…corresponded to the torsion of the methyl groups and the modes above at 930 cm -1 were associated with, as suggested by Lorriaux et al [55], the C-H in-plane bending and the Ph-N=N-Ph in-plane bending vibrations. The intensities of the out-ofplane C-H and the torsion C-C vibrations calculated between 940 cm -1 and 990 cm -1 were too low to be visible in the spectra.…”

“…Hence, we can conclude that the coupling between the phenyl-N stretching and the CH in-plane bending mode 9a′ is weak for this mode in comparison to the mode around 1159 cm -1 . Lorriaux et al [55] have suggested linking the bond orders of the N-phenyl bonds of different azobenzene derivatives to the observed shift of this band. With this consideration, a high bond order would indicate a short bond length and a high wave number.…”

“…Finally, a medium intensity band was experimentally observed at 1189 cm -1 , 1193 cm -1 , and 1200 cm -1 for ABOH, DR1, and DO3 respectively. Until the 80's, the assignment of this mode was speculative as confirmed by the discrepancies between the authors′ statements summarized by Lorriaux et al [55]. Based on normal coordinate calculations and the approximate atomic displacements, we decided to assign the bands around 1190-1200 cm -1 to a coupling of the N-phenyl stretching and the CH in-plane bending mode 9a′.…”

“…For 4,4′-azobis(pyridine N-oxide), the band observed at 927 cm -1 was also attributed to these vibrations [54]; whereas for para-substituted azobenzene derivatives, Lorriaux et al [55] suggested that these bands be associated with the C-H in-plane bending and the Ph-N=N-Ph in-plane bending vibrations. According to our results, only one mode was revealed for ABOH and DO3 at 931 cm…”

Photoinduced Orientation of Azobenzene Chromophores in Amorphous Polymers As Studied by Real-Time Visible and FTIR Spectroscopies

“…This last absorption band is overlapped by the ν 19a (CdC) stretching vibration of the para-substituted phenyl rings. [37][38][39][40] The PM-IRLD spectrum recorded on the 5% DR1 doped PMMA film irradiated during approximately 1 h is presented in Figure 3B. As seen on the figure, the signal-to-noise ratio of this difference spectrum is remarkable, even though the ∆A for the strongest band is only -0.03.…”