Vibrational Analysis of Polyaniline:  A Model Compound Approach

Abstract

In this work, we have used an oligomer model compound approach for the understanding of the vibrational spectra of the principal forms of polyaniline. Selected model compounds have been studied by Raman and infrared (IR) spectroscopies. The observed vibrational bands are assigned to the expected modes, by revealing the relationships between molecules. In a more theoretical part, dynamical calculations on the different model compounds and their related polymers are presented. The use of model compounds allows us to reach better sets of force constants, as soon as we assume that the parameters can be transferred to the polymeric forms. The obtained values of these force constants are discussed in regards to the oxidation state of polyaniline and its corresponding geometrical structure.

Polyaniline: The infrared spectroscopy of conducting polymer nanotubes (IUPAC Technical Report)

“…3). The most pronounced band at 823 cm -1 in the substitution region (900 to 650) cm -1 in the spectrum of H is due to the C-H out-of-plane bending vibrations of two adjacent hydrogen atoms on a 1,4-disubstituted benzene ring [23,[32][33][34]40]. This confirms the dominating para-coupling of constitutional units in PANI chains.…”

“…The absorption band at 1307 cm -1 in the spectrum of the sample H corresponds to π-electron delocalization induced in the polymer by protonation [29]. This band is weaker in the spectrum of the corresponding base H-B and corresponds to the C-N stretching vibration of a secondary aromatic amine [23,40]. The band characteristic of the conducting protonated form is observed at 1248 cm -1 in the spectrum of sample H. It has been interpreted as corresponding to a C-N +• stretching vibration in the polaron structure [41].…”

“…The band characteristic of the conducting protonated form is observed at 1248 cm -1 in the spectrum of sample H. It has been interpreted as corresponding to a C-N +• stretching vibration in the polaron structure [41]. The spectrum of the sample H exhibits a strong and broad band centered at 1148 cm -1 , which has been assigned to the vibration mode of the -NH + = structure, and is associated with the vibrations of the charged polymer units Q=NH + −B or B−NH +• −B [23,32,40]. This indicates the existence of positive charges on the chain and the distribution of the dihedral angle between the quinonoid and benzenoid rings.…”

“…It is known that the frequency of C-N stretching vibrations is largely determined by the aromatic character of the carbon atom [33]. The strong band at 1299 cm -1 (for Ac-B) is due to the C-N stretching vibrations of aromatic amines [23,40] associated with para-linked aniline units, and is downshifted relative to the band at 1305 cm -1 for the sample H-B. We observe a maximum at 1167 cm -1 , which is primarily due to the aromatic C-H in-plane deformation and a sharper shoulder at 1146 cm -1 in the spectrum of the sample Ac-B.…”

Vibrational Spectroscopy of PTSA—Doped Polyaniline

“…IR transmittance spectra of EB and (0.5M and 1.0 M) PTSA doped PANI recorded for 4000 -400 cm"^ region are presented in Figure 1 and Figure 2 These spectra show vibrational peaks of B ring, Q ring, their combination modes and semiquinone units in PTSA:ES and their assignment is made by using Oligomer Compound Approach [6][7][8][9]. The stretching vibration of hydrogen bonded secondary amine group is observed as strong broad band at 3447 cm"^ in EB and with reduced intensity in PTSA doped salts.…”