Cationic dyes as morphology-guiding agents for one-dimensional polypyrrole with improved conductivity

Polypyrrole was prepared in the presence of cationic dyes, safranin and phenosafranin. The safranin supported the one-dimensional growth of polypyrrole, converting globules to nanorods and later also to nanotubes, particularly at higher dye concentrations. In the case of phenosafranin, the produced nanotubes were considerably thicker and were always accompanied by globules. Upon oxidation both dyes are expected to generate insoluble oligomeric templates that serve as loci for the deposition of polypyrrole. The formation of globular morphology takes place when the dye becomes depleted, due to its low concentration for safranin, or because of robust templates produced by phenosafranin. In addition to scanning and transmission electron microscopies, the resultant polypyrroles were characterized by FTIR and Raman spectroscopies, and DC conductivity measurements. The conversion of globular morphology to nanotubes/nanofibers was accompanied by the increase in conductivity from 5 to 35 S cm(-1), which was explained by the improved ordering of polypyrrole chains more preferable for charge transport. The series of syntheses at varying oxidant-to-pyrrole mole ratios confirmed the stoichiometric ratio 2.5 to be the best for pyrrole oxidation but a good stability of polypyrrole was demonstrated even at extremely high stoichiometric ratio 15.