ИСТИНА

The acid doping process of polyaniline oligomers: phenyl-phenyl-capped dimer, phenyl-NH2-capped trimer and tetramer, and the mixture of higher oligomers, was studied in solutions in dimethyl sulfoxide and other organic solvents. Low molecular weight and polymeric sulfonic acids were used as dopants. Studying acid doping of phenyl capped aniline dimer in oxidized and reduced states we found that complete conversion of all molecules to the radical form is achievable in this system via intermolecular bipolaron splitting [1]. Similar intermolecular interactions could contribute to charge carrier formation during the acid doping of polyaniline and open the possibility of regulation of effective redox state of the doped polyaniline by addition of phenyl-phenyl-capped aniline dimer. Studying acid doping of phenyl-NH2-capped trimer and tetramer, and the mixture of higher oligomers, we found that both in case of use of polymeric acids as doping agents and in case of use of huge excess of low-molecular weight acids, the long-wavelength absorption band appears in the UV-vis-NIR spectra of aniline oligomers. This absorption band with the maximum at the wavelength of more than 1000 nm looks similar to “free-radical tail” observed in highly conductive polyanilines. We propose that appearance of this band could be caused by the “excessive” doping of aniline oligomers, which include not only protonation of imine nitrogen atoms but also protonation of amine nitrogen atoms with further changes in molecule configuration and charge carriers redistribution. References [1] O.E. Bogomolova, V.G. Sergeyev. J. Phys. Chem. A, 2018, 122 (2), pp 461–469. O.Bogomolova acknowledges financial support from the Russian Science Foundation (Project No 17-73-20266).