ИСТИНА

Polyaniline oligomers – low molecular weight models of polyaniline, one of the most interesting conducting polymers. Acid doping (protonation) of polyaniline leads to generation of conductive salt form. Conformational and self-assembly effects in doped polyaniline can influence its conductivity, stability and other properties. According to complex structure of polyaniline some of these effects are easier to study on model compounds. Here we present the study of trianiline, tetraaniline and mixture of longer polyaniline oligomers doped by various acids in different solvents. It was found that acid doping of tetraaniline or polyaniline oligomers mixture with polyacids (poly(4-styrenesulfonic acid) or poly(2-acrylamido-2-methyl-1-propane-sulfonic acid)) in DMSO lead to appearance of a new absorption band in UV-vis-NIR spectra. This band is intensive, quite sharp in case of tetraaniline, broader in case of oligoaniline mixture and characterizes by the maximum at the wavelength of more than 1000 nm. The result is nearly the same for both polyacids. The same spectral changes appeared to be achievable by addition of large excess (orders of magnitude) of low-molecular weight acids (camphorsulfonic, dodecylbenzene sulfonic, HCl) to tri- or tetraaniline. Addition of low-molecular weight electrolyte (NaCl) lead to opposite changes in spectra of doped tetraaniline. In case of polymeric dopant intensity of the long wavelength absorption band decrease with the increase of NaCl concentration, while in the case of low molecular acid – increase. This long wavelength absorption band in UV-vis-NIR spectra of polyaniline oligomers is similar to one observed for highly conductive well ordered polyaniline. The effect can be explained by conformational changes (stretching) of oligoaniline molecules or, less probably, by self-assembly of oligoaniline molecules with J-aggregates formation.